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'I CIMMYT INTERNATIONAL MAIZE AND WHEAT IMPROVEMENT CENTER

CENTRO INTERNACIONAL DE ME}ORAMIENTO DE MAIZ Y TRIGO

Sustainable Maize and Wheat Systems for the Poor Maize and Wheat Improvement Research Network for the Southern African Development Community

(funded by the European Union)

MAIZE TRAINING MANUAL

LECTURE NOTES OF THE FIRST REGIONAL MAIZE TRAINING COURSE FOR TECHNICIANS FROM MALA WI, TANZANIA, ZAMBIA AND ZIMBABWE

ARUSHA, TANZANIA

JUNE 1- 11, 1997

EDITED BY BATSON T. ZAMBEZI

MAIZE AND WHEAT IMPROVEMENT RESEARCH NETWORK (MWIRNET) FOR SADC

Address: CIMMYT, P. 0. Box MP 163, 12.5 km peg Mazoe Road, Mt. Pleasant, Harare, ZIMBABWE

Phone: +263.4.301.945 / 301.807 Fax: +263.4.301.327 Email: [email protected]

CONTENTS

Section Page

1. The maize plant H.B. Akonaay 1

2. Management of maize nurseries N.G. Lyimo 11

3. Management of maize trials Z.O. Mduruma 15

4. Principles of plant breeding B.T. Zambezi 32

5. Population improvement Z.O. Mduruma 37

6. Hybrid maize development N.G. Lyimo 44

7. Fertilizers- definitions and calculations J.D.T. Kumwenda 54

8. Soil and plant analysis J.D.T. Kumwenda 67

1. Weed control J.D.T. Kumwenda 69

"0. Striga control J.K. Ransom 76

.1. Common problems in maize trials J.D.T. Kumwenda and B.T. Zambezi 80

2. Glossary of breeding terms Z.O. Mduruma, N.G. Lyimo, H.B. Akonaay 83

3. Acknowledgments 89

4. Annex 1 course evaluation 90

5. Annex 2 list of participants 92

5. Annex 3 course time table 95

1. THE MAIZE PLANT

Herman Akonaay

1.1. Description and botanical relationships

Maize as a member of the grass family, Gramineae has many characters common to other grasses, such as conspicuous nodes in the stem, a single leaf at each node, the leaves in two opposite ranks i.e. distichous, each leafhaving a sheath surrounding the stem and an expanded blade connected to the sheath by a blade joint. As in other grasses there is a tendency to form branches at the nodes and adventitious roots at the base of the intemodes. The lower branches may take root and develop into stems known as tillers or suckers which resemble the main stem, whereas the others develop as rudimentary or functional ear shoots.

Maize is a monoecious plant with its functional staminate flowers bome in the tassels which terminate the stems, and its functional pistillate flowers bome in the ears which terminate all but the basal branches or tillers. The heritable vegetative size of plants varies greatly with variety and regional adaptation.

In most grasses the elongated intemodes become hollow, but in the members of the tribe maize Maydeae (Tripsaceae) and the sorghum tribe Andropogoneae the stems remain solid.

1.1 .1 . Origin of maize

No wild plant is known from which maize could readily have been derived. This might be accounted for by the assumption that the wild maize plant has become extinct. Teosinte is usually regarded as very closely related to maize; not only because of its morphological resemblance, but also because it can be hybridised readily with maize, the progeny being fertile. Upon crossing, the chromosomes pair normally and crossing over takes place between com and Teosinte chromosomes. Teosinte is also susceptible to such common maize diseases as maize smut and maize rust.

The geographic point of origin is generally conceded to be somewhere in the tropics of Central or South America with the latter seeming most probable. This belief is based upon archaeological and ethnological evidence and upon the theory that the birth place of a new species is likely to be found in the region of its greatest variability.

1.2. Development and structure of vegetative parts

As an aid to tracing the origin of the vegetative parts of the maize plant the anatomical discussion is given here with a brief description of the Kemel and its parts.

1.2.1. The Kemel or 'Seed'

The maize kemel is not merely a seed but a one seeded fruit, in which the seed, consisting of embryo and endosperm and remnants of the seed coat and nucellus is pennanently enclosed in the adhering pericarp. Upon shelling, the flower stalk or pedicel commonly remains attached to the base of the kemel.

1.2.2. Pericarp

The pericarp or transformed ovary wall forms the tough outer covering of the kemel, it furnishes protection for the interior parts. At the apical end of the kemel the peri carp bears the silk scar and the basal end it merges into the tissues of pedicel or tip cap as it is often called.

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1.2.3. Endospenn

When the pericarp and the adhering remnants of the seed coats and nucellus are removed which can easily be done after soaking the kernels in water, only the endosperm and embryo are left. The endosperm makes up the greater part; the relatively small embryo being situated on one side near its base.

1.2 .4. Embryo

The embryo or young maize plant is embedded near one face of the endosperm at the base of the kernel or caryopsis. It has a central axis which is terminated at the basal end by the primary root and at the other end by the stern tip. The stern comprises five or six short internodes and bears a leaf at each node. The first leaf known as the scutellum is attached to the scutellar node. This is modified as a food storage organ and serves to digest and absorb the endospenn during growth of the embryo and seedling.

The second leaf, the coleoptile is attached to the second or coleoptilar node and is modified as a protective covering for the plumule or first bud of the plant which it spearheads through the soil upon gennination.

1.2.5. Pedicel

The tissue of the pedicel or flower stalk merges into those of the ovary wall without close demarcation between the two. Upon shelling from the cob, the pedicel with adhering lemma and palea usually remains attached to the kernel.

1.3. Seed germination and seedling development

When the maize kernel is placed under moisture and temperature conditions are favorable for germination, growth activity is quickly resumed by the embryo. After the soil has warmed up, full emergence may take place in about 5 days. Healthy, well preserved seed usually has high viability of 95-1 00%. The chief cause of loss in germination is iJ1iury from freezing (in temperate countries). This results from exposure to low temperatures while moisture content is still high. A second cause of reduced viability is infection with seed borne or soil borne rot organisms. Improper storage conditions which delay drying may cause damage with loss of viability. During germination the organs of the embryo which were fonned during the development of the kernel and have remained dormant in the dry seed resume their growth and development. The primary root and its enclosing sheath, the colerhiza elongates and breaks through the pericarp. The root soon breaks through the end of the co/eorhiza. The plumule and its enclosing sheath the coleoptile, begins to elongate and also breaks through the pericarp of the kernel. At first the coleoptile grows faster than the plumule but when it reaches the surface of the soil and is thus exposed to the light it soon ceases to grow and the plumule breaks out through its tip. About the time the tip of the coleoptile reaches the soil surface the first crown roots appear immediately above the coleoptile node and later an additional whorl of roots forms at the base of each succeeding 6 to 10 internodes of the stern. These crown roots soon form the major part of the root system of the plant.

1.3. The root system

The root system of maize, as of other grasses consists of two sets of roots:

1.3 .1. Seminal roots

These consist of the radicle or primary root and a variable number of lateral roots which arise adventitiously at the base of the first internode of the stem. The radicle is always present

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except when killed by some injury, such as, freezing. It may be the only seminal root as is frequently the case in some flint varieties or there may be averages of one to seven lateral seminal roots in various dent maize varieties.

1.3.2. Adventitious roots

These constitute the principal part of the root system after the seedling stage. Any aerial brace roots are also included in this category. The first whorl of 4 or 5 crown roots appears at the base of the second internode about as soon as the tip of the coleoptite reaches the soil surface. A few of the succeeding higher internodes may have about the same number, after which the successive ones have more and larger roots up to a little above the soil surface. Those from about the lower five internodes like the seminal roots grow horizontally for some distance before turning downwards, while those from the higher internodes which appear later in the season grow downward at once. The functional crown roots average 85 per stalk with a total combined length of about 350 feet. These roots are all branched and rebranched so that the total length of the roots is about 6 miles per plant.

1.4. The stem

A typical maize stem consist of about 24 alternating nodes and internodes. About 8 internodes remain very short and under ground forming an inverted cone - shaped basal end of the stem known as the crown. The crown inter-nodes give rise to the adventitious crown-root system and adventitious brace roots may develop at the base of one to several aerial internodes. Under favorable growing conditions, the above ground internodes are distributed over a stem length of about I 00 inches or more. With its greatest diameter of about 1 1/4 inches near the ground level, the stem gradually tapers towards its tip. Each of the lower internodes adjacent to an ear shoot becomes permanently grooved throughout its length as a result of the pressure of the developing shoot during early growth.

1.5. Leaves of the seedling and mature plant

Upon gern1ination the leaves already formed in the embryo resume growth and the formation of the leaf is resumed and continues until all the leaves have started and the growing point of the stem begins to form the tassel. The total number of leaves formed varies both within and between varieties. Some varieties have been found to average 17 leaves attached above ground and 6 under ground. Not all these are functional at any one time, as some of the lower leaves are lost before the upper ones have expanded. The lower leaves tend to be tom loose and destroyed by formation of the crown roots and enlargement of the stem. Under favorable conditions the blades of the surviving leaves of full-grown stalks total about 1400 square inches in area.

The fully formed leaf consists mainly of the blade which is thin except for the midrib. The blade tapers gradually towards the tip and slightly towards the base, until it abruptly narrows where it joins the sheath. Both blade and sheath have parallel veins which are united by cross connections at irregular intervals.

1.6. Development and structure of the reproductive organs

Maize being monoecious, bears staminate flowers in the tassels and pistillate flowers on the ear shoot. The main stem terminates in a staminate inflorescence or tassel, as do the basal branches or tillers when present. The branches arising from nodes above the soil surface tenninate in a pistillate int1orescence or ear, but usually all soon degenerate except the upper one or two located about midway on the stalk.

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1.6.1. Shedding of pollen

At anthesis, just before pollen is shed, the lodicules swell to several times their former size and pry the lemma and palea apart, making it possible for the anthers to be extended by the elongating filaments. Soon the anthers break open near the tip, forming pores through which the pollen escapes. Little pollen is shed until the anthers are shaken by the wind or otherwise disturbed. This tends to insure a high percentage of cross pollination under ordinary field conditions. In each plant the tassel usually sheds some of its pollen before the silks of its ears emerge from the husks, but the tassel normally continues to shed for several days after the silks are ready to be pollinated.

A tassel begins to shed pollen a short distance below the tip of the central axis and pollen shedding progresses both upwards and downwards reaching the tip of the central axis long before it reaches the base. A tassel may shed pollen tor a week or more.

1.6.2. Amount of pollen produced

Pollen grains are produced in large numbers as is the rule with wind pollinated plants. A maize plant can produce about 25,000,000 pollen grains. Thus 25,000 pollen grains are produced for each kernel, on an ordinary ear with 1 000 kernels.

1.6.3. Development of the ear shoot

An axillary branch bud forms at each node of the stem up to the one which bears the upper most ear. Each bud is enclosed in a leaf like structure, the prophyllum. At first those buds which will develop into ear shoots are like those which form tillers but differences soon appear. In tillers the prophyllum remains small and soon dies, whereas in ear shoots it becomes large and persists as one of the husks.

1.7. Reproduction and kernel development

When pollen is shed by the tassels, only that which is intercepted by fresh silks can germinate and where several pollen grains germinate on the silk usually only one functions in fertilisation. Most of the pollen is lost by falling to the ground or is caught by the leaves and accumulates in the leaf axis. In pollination, the pollen is usually caught by the hairs of the silk although it may function when caught on the body of the silk. The silk supplies the pollen with moisture which causes it to germinate, sending out a pollen tube through the germ pore.

1. 7 .1. Fertilisation

When the tip of the pollen tube reaches the micropyle it grows between the protruding cells of nucellus tissue until the embryo sac is reached. On entering the embryo sac the end of the pollen tube ruptures, setting free the two sperms. The nucleus of one sperm fuses with the egg nucleus, forming the zygote within which the chromatin from both sources completely intermingles. The other sperm nucleus fuses with one of the polar nuclear and this fused nucleus in tum fuses with the other polar nucleus, thus establishing the primary endosperm nucleus with 30 chromosomes. This double fertilisation explains how characters of the male parent may show up in the endosperm, as well as, in the embryo and the new plant within which it will develop.

1.8. Making hand pollinations

1.8.1. Floral characteristics of the maize plant

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The com plant is monoecious, with the male flowers in the tassel and the female flowers on the ear shoots. When the male flower is mature the anthers are exserted from the spikelet, and pollen is dispersed through a pore at the tip of the anther. Anther exsertion begins on the central spike a short distance below the tip. Each spikelet has two flowers and the anthers are exserted from the upper flower first and then from the lower flower, either later the same day or the following day.

Pollen shed for a tassel may vary from only I or 2 days to more than a week depending upon temperature, humidity, air movement and genotype. Pollen is dispersed by wind currents, as a result, extensive cross pollination and little self pollination occurs on an individual basis. Insects cause an insignificant amount of pollen dispersal but they can cause contamination in controlled self or cross pollination. The amount of pollen dispersed from one tassel will vary among genotypes. Hybrids normally shed more pollen for a longer period compared to inbred lines. The top ear shoot usually is at the sixth or seventh node below the tassel. There is axillary bud at each node below the top ear node, but elongation of the cob and silk emergence occurs at only the upper 2 or 3 nodes.

The silks that emerge from the tip of the ear husk are the functional stigmas and there is one silk for each potential kemel. The first silks to emerge usually are from near the basal part of the ear. Complete emergence many occur in only 2 or 3 days under favorable growth conditions or may require 5-7 days with cool temperatures. The silks usually emerge at the top ear node I to 3 days after anther dehiscence has began. Tassel development seems to control development of the ear shoot. This dominance is greatest for genotypes that produce only one ear per plant. Prolific genotypes don't have dominance for the tassel and thus their silks frequently emerge before the tassel begins to shed pollen. Silks become receptive as soon as they emerge from the ear husk. The length of time for receptive silks on the ears is determined by the time required for all silks to emerge from the husk and time a silk remains receptive after emergence. Data indicate that it may require up to 5 to 6 days for all silks to emerge from the ear. Receptivity up to I 0 days after emergence has been reported.

Selfing and crossing are essential procedures in breeding crop plants. It is important that the breeder masters these procedures/techniques in order that he may manipulate pollination according to his needs. The exact procedures that he may use to ensure self or cross pollination of specific plants will depend upon the particular species with which he is dealing with; structure of the flowers in the species and the normal manner of pollination. Thus he should know the flowering habit of the crop. Selfing or inbreeding of self-pollinated crops offers no particular problems to the breeder, as this follows the normal mode of pollination of these crops. This is the procedure used for crops like wheat, rice, barley, pulses, soybean and groundnuts. However, the breeder should know something about the extent of natural crosspollination within his breeding material. If it is slight, this natural crossing may be ignored in this normal breeding procedure; but if natural cross pollination is excessive or if precise results are desired, it may be necessary to protect the flower by bagging to prevent foreign pollen from reaching the stigmas. In the selfing or inbreeding of cross-pollinated species it is essential that tl1e f1ower be bagged or otherwise protected to prevent natural cross pollination. In the cross-pollinated species of grasses which are normally pollinated by wind blown pollen, bagging the heads with parchment or glassine envelopes is a normal practice. Seed set is frequently reduced in the heads enclosed in bags because of excessive heat inside the bags. In maize a bag is placed over the tassel to collect pollen and the shoot is bagged to protect it from foreign pollen. The pollen collected in the tassel bag is then transferred to the ear shoot.

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1.9. Preparation of the female for pollination

The ear shoot (husk tip) must be covered by an ear shoot bag before the silks emerge from the husk tip. Ear shoots may be covered any time during the day, but it frequently is the first operation of the day. The length of ear shoot development from the leaf axil before silks begin to emerge will vary among genotypes and is affected by environmental conditions. The ear shoot bag should be placed so that it is firmly anchored between the shoot and the auricle of the ear leaf. Sometimes it may be necessary to break off the ear leaf and pull the bag down so that it is anchored between the shoot and the stalk. The best ear shoots to use in self or cross pollination exercise will have had their silks emerged under the shoot bag for 2 to 3 days. If a covered shoot has silks emerged more than 2 to 3 days before it can be used, it may be necessary to trim the silks to prevent them growing out of the bag and becoming contaminated. On the day preceding intended pollination, the extended/overgrown silks are cut to within 2 em of the husk tip. This procedure will cause the formation of a brush of silks on which the pollen can be spread the next day. If it is necessary to use the ear before all silks have emerged, it may be convenient to cut the ear shoot to within 2 em of the cob tip, so that all silks will be available the next day. The shoot bag must be replaced securely after preparation of the ear shoots.

1.10. Pollination

A tassel normally produces its greatest volume of pollen in the second and third days of dehiscence. When the ear is prepared for pollination the tassel earmarked as the source of pollen is covered by a tassel bag the same day. The tassel should have at least 1 day of anther exsertion and pollen dehiscence. The tassel bag is placed over the tassel on the day before pollination to eliminate contan1ination by other pollen that may adhere to the tassel and it will hold all pollen shed by the tassel while the bag is in place. The bag is held in place by a paper clip or a staple.

Pollen may be collected and used immediately from uncovered tassels that are dehiscing. This procedure may be convenient in a cross-pollination program in which several ears are pollinated by pollen from one tassel or a pollen composite from several tassels. For selfpollination the pollen is taken from the tassel and placed on the silks of the same plant. With reasonable care, contamination will be infrequent because of the excessive amount of pollen from the intended source in proportion to foreign pollen.

For cross-pollination, pollen from one tassel is used for one or several ear shoots simply by pouring pollen from the pollen bag directly on to the silks of another plant. Where several pollinations are made and pollen from several tassels is composited, a pollen gun may be used. Clumping of the pollen may occur, particularly, if humidity is high; a hU111idity control compound may be used to keep the pollen dry. The pollinating operation must wait until anthers are exserted and pollen is released. This may be about 3 hours after sunrise but may be later in the day, depending upon temperature and humidity. The silk is exposed for pollination either by lifting the ear shoot bag or by tearing off the closed end of the bag. After the pollen has been dusted onto the silk, the tassel bag is quickly placed over the ear shoot, pulled down toward the ear node and fastened around the stalk either by non-slip paper clip or staple. If the ear shoot bag is left in place after pollination, it may prevent contamination that might be caused by insects that may chew holes in the tassel bag. On the other hand, in some seasons when the ear shoot bag is left in place, it may cause considerable ear-tip rot by harvest time. Marking on the tassel bag may be necessary to identify parental materials. A moderately soft graphite pencil is ideal. Limited marking is desirable to save time. Large

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numbers or letters should be used when marking on the bag because it may be partly torn before the ear is harvested.

1.11. Seed production and maintenance - General principles to be borne in mind in the process of seed production

1.11.1. Agronomic management

Husbandry practices applied in maize seed production fields are in general similar to those used in a commercial grain crop. However, there are some additional requirements peculiar to seed production, namely:

• Value of good seed is higher than that of grain. Therefore a seed crop warrants greater care and more inputs than a grain crop.

• It is important to realise the goal of obtaining the maximum number of high quality genetically pure seeds while minimising the risk.

• Realise that care taken in the selection and preparation of the seed field to obtain the most uniform growing environment possible will greatly facilitate identification of off-type plants in future rouging operations.

• Careful consideration must be given to the acreage planted, taking into account projected sales, labor availability during critical periods such as detasseling.

1.11.2. Site selection criteria

The following considerations should be borne in mind:

• Adaptation of the variety/crop to the production environment, i.e. select sites which will allow reproduction of all plants to reduce the risk of rapid shifts of genetic make-up of a given variety.

• Previous cropping history - it is advisable to plant in a field previously sown to another crop to reduce problem of a volunteer crop.

• Consider field topography, weed populations and soil fertility. • Condition in neighboring fields - find out phmting date and variety selected in order to

determine if there may be an isolation problem. • Accessibility of site to transport in relation to input centers and processing facilities. • Contract farmer selection.

1.11.3. Isolation

The cross-pollinated nature of maize plus its abundant production of light, wind carried pollen, often make it very difficult for seed producers to avoid contamination. Thus proper isolation is essential to limit contamination from foreign pollen and thus ensuring the production of genetically pure seed. Isolation is accomplished in 3 ways:

• Perfect nick - this occurs when pollen parent starts shedding pollen just before silk emergence in the female parent rows.

• Distance - This is affected by border rows in that pollen from border rows dilutes contamination. Natural barriers may also reduce contamination. Similarly, abundant supply of pollen from male parents at the right time may be effective in reducing contamination.

• Minimum isolation distances have been established as follows


Category Hybrids OPV s/Composites:

Breeder's Absolute 300m Foundation 400m 300m Certified 200m 200m

• Time isolation - Seed materials may be planted at different times, e.g. one to two-week spacing. This is more practical under irrigation. When stagger planting, always start with the earliest material.

1.11.4. Planting

Planting in maize seed crop differs from that of commercial crop in that border rows are often required; a lower plant density is often recommended and when producing a hybrid two components rather than one are sown in a given field. This latter aspect often complicates the planting. Planting operations that may be adopted for hybrids for better seed set involve ratios ranging from 2: 1 to 6: 1, depending principally upon pollen production ability of the male parent.

One important problem facing breeders and seed producers of hybrid maize is the use of parents that differ in their time of flowering. Various methods have been used to achieve a good nick including:

• Delayed or split planting. • Double planting of male rows. • Variable depth of planting - deeper sowing delays flowering. • Variable use of starter fertiliser. • Foliar fertiliser applications. • Seed coat treatments.

1.11.5. Roguing

This is systematic evaluation of a seed production field and the removal of all undesirable plants. The goal of this operation is to assure the desired varietal, genetic and physical purity in the seed production field. It is the most effective and important method of contaminant removal because it both prevents contamination and eliminates existing contaminants, prior to planting, at planting, during the vegetative cycle, prior to flowering, during harvest, processing and storage.

1.11.6. Detasseling

Detasseling period is usually the most critical and difficult to manage period in maize seed production. To achieve the necessary genetic purity standards all tassels from the female parent rows must be removed prior to shedding pollen and/or before silking. The detasseling operation involves a physical removal of tassels either manually or in combination with mechanical devices.

• The detasseling period normally takes about 2 weeks but may range from 1-5 or more weeks. This period may be prolonged in fields which have:

• Delayed and non-tmifonn germination. • Variation in soil fertility. • Waterlogging in early stages. • Serious pre-flowering water stress • High incidence of foliar diseases.


Factors influencing the magnitude and complexity of detasseling operations include:

• Tassels must be removed from all female plants before shedding and silk emergence • Under favorable weather conditions this is a 7 -day work. • Some female-parent plant types are more difficult to detassei. • Female parents whose tassels begin shedding pollen before fully emerging from the upper

leaves or which extrude silks at the same time as pollen shed occurs create difficult detasseling supervision or management problems.

• Weather conditions can significantly aid or complicate the detasseling activities.

1.11.7. Field inspections

Field inspection is done by qualified inspectors • Public relation and education of the seed grower. • Identification of sources and levels of physical and genetic contamination leading to

acceptance or rejection of the crop.

Inspectors are required to have thorough knowledge of:

• Varietal characteristics of the crop. • Common diseases of the crop. • Conm1on weeds especially prohibited or injurious weeds. • Abnormalities ofthe crop including nutrition, temperature, moisture stress effects, drought

etc. • Practices and conditions for production of high quality seed. • Specific tolerances of contaminants.

1.11.8. Objectives of the field inspection include verifyii1g that the seed crop is:

• Grown from an approved seed source. • Grown in a field meeting prescribed land requirements as to the previous crop. • In compliance with prescribed isolation standards and number of border rows. • Planted with prescribed ratios of female and male parents. • Properly rogued. • True to varietal characterisation.

Harvested properly to avoid mixture.

1.11.9. Varietal characterisation

An accurate description of morphological traits is an important guide for maintenance and multiplication of seeds, whether they are inbreds or OPVs. Failure to develop appropriate varietal descriptions is often a source of conflict between breeders and seed producers. Breeders must recognise their responsibility to describe their relea<;ed materials in an accurate and timely fashion. Below is a table which shows the characteristics which are considered in describing a variety.


Table 1.1. Characteristics that may be considered in the description of a maize variety

Plant parts Characteristics Qualitative Quantitative

Stem color height

Leaves

Tassel

Ear

Seed

color of leaves color of central vein color of the sheath pubescence of sheath

color of glumes color of anthers compact or open

color of stigmas color of dry husks husk pubescence husk texture ear shape kernel rows arrangement cob color

color of pericarp color of aleurone color of endosperm texture (dent/flint)

1.11 10. Harvesting seed maize

number of nodes number of tillers

total number of leaves no. ofleaves above ear leaf angle width of ear leaf length of ear leaf

length of peduncle length of central axis no. of branches days to 50% pollen shed

no. per plant insertion angle length of ear peduncle no. ofkernel rows length diameter weight shelling% cob color

length width weight of 1 000 seeds thickness of seed

Harvesting may start as early as when developing kernels approach physiological maturity (30-35% moisture range). Normally at this point seed quality is at maximum. However, for economic reasons harvesting is delayed until moisture drops to 20-25% range, the cob seed maize is placed in special cribs for further drying. In a farmer's field, maize for seed should be harvested first before harvesting the rest of the maize.

If the seed is to be shelled, moisture level should be below 20% to minimise damage. Prompt harvesting of seed maize:

• Reduces risk of delays due to adverse weather conditions.


• Reduces losses from insect damage. • Reduces bird damage. • Reduces losses from ear and stalk rots and other diseases.

1.11.11. Grading and starting seed maize

During sorting and grading maize seed cobs which are damaged (mechanical, insect, etc.) and cobs with excessive deviation in terms of the varietal description are removed. The remaining ones are then graded into large, medium and small; with the largest category going for the 1st grade seed, then 2nd grade seed, etc.

Storage for maize seed is usually a bit different from storage of commercial maize grain in that after shelling, seed maize should be well treated with suflicient doses of insecticides (dressing), labelled with two labels, one inside a container and the other on the outside and then sealed. Thereafter, seed is put in store awaiting disposal. It should be emphasised that the seed should be stored far away from commercial maize at farmers level.

1.12. References

CIMMYT, 1984. Development, maintenance, and seed multiplication of open-pollinated maize varieties.

CIMMYT, 1985. Managing trials and reporting data for CIMMYT's International Maize Testing Program, Mexico. D.F.

Kiesselbach, T.A. 1980. The Structure and Reproduction of Corn. University of Nebraska Press.

Poehlman, J.M.; and D. Borthakur. 1969. Breeding Asian Field Crops. Oxford and IBH Publishing Co.

Ritchie, S.W., J.J. Hanway, and G.O. Benson. 1989. How a corn plant develops. Special Report No. 48, Iowa State University of Science and Technology Co-operative Extension Service, Ames, Iowa.

Taba, S. (Ed). 1995. Maize Genetic Resources. Maize Program Special Report, Mexico, D.F.:CIMMYT.

2. MANAGEMENT OF NURSERIES

NickLyimo

Crop research is an expensive undertaking requiring proper management, right from the seed bed preparation, seed preparation, plot layout and planting stages, through data collection and harvesting, and finally, seed storage.

2.1. General considerations in field nursery operations

Careful planning of the layout of nurseries can ensure the efficiency that is desired in carrying out various nursery activities, from planting through harvesting. The largest portion of time spent in the nursery involves taking notes and making hand pollinations. It is, therefore, necessary that these operations be given highest priority when plruming the layout of nurseries. The following suggestions may help in ensuring proper nursery layouts in order to save time and to eliminate unnecessary activity in the field.

2.2. Location and arrangement

Try to locate and arrange the material in blocks according to the type of study or the intended pollination procedure. e.g. hybridization (crossing) blocks, selfing blocks, etc.


If, for example, it was desired to cross a set of inbred lines to a common tester, this could be accomplished by planting the material in an isolated crossing block, so that the top crossing could be accomplished through natural crossing, as shown below.

Natural crossing (Isolation plot)

TTABCDTTEFGHTT I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

or

Direction of prevailing winds

TATBTCTDTETFTGT I I I I I I I I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I ! I I I I I I I I I I I I I I I I I

T: tester rows Entries to be tested: A, B, C, ... , etc.

Alternatively, if isolation is not possible, the tester may be planted in paired rows with the materials to be evaluated as shown below. Hand pollinations are made between rows and the tester may be used either as the male or female parent. If there is a wide range of maturity among the materials to be evaluated, matings may be more efficiently accomplished by planting the materials to be evaluated in separate blocks in order of increasing number of days to flower. The tester is planted in adjacent blocks with specified rows delayed appropriately, to effect the desired pollinations.


Making crosses by hand

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I I I II I I I I I I I I I I I I II I I I II I I I I I I I I I I I I I I I I I I I I I II I I I II I I I I

or Alley

I I I I I I I I I I I I I I I i I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I TTTT T TTTTTTTT T

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Alley

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ; II I I I

I I I I I I I I I I I I I I I T TTTTT TJ KLMNO P Q

T: tester rows Entries to be tested: A, B, C ... , etc.

2.3. Numbering of plots

Procedures for nwnbering of plots within the nursery very much depend on individual preferences. The most important thing is to ensure that the numbering system adopted is adequate for the proper identification of materials in the field.

In addition to plot numbers, for example, some breeders prefer to specify block and even range numbers. E.g. 3042 represents plot 42 in block 3, or B1508 represents block B, range 15 and plot 8, in which a range is a series of plots perpendicular to the alley separating the plots. Irrespective of the numbering system used, a field map and field book should be prepared for ease in locating materials in the nursery, and for recording various types of data.

2.4. Plot identification materials

Plots in the nursery may be identified with stakes placed at the front of the plot or with tags attached to the first plant in the plot. For some blocks, it may be necessary to identify each plot with plot number, entry designations and possibly, pollinating instructions, e.g. sibbing, crossing, selfing, etc. Tags or stakes with different colors may be used to identify special materials, for example if more than one tester is used in a top-cross nursery block.

2.5. Keeping of breeding records

The maintenance of adequate and accurate breeding records is of prime importance in any crop breeding or genetics program. The kinds of records maintained differ very much among individuals and it may be difficult to identify any commonly used system. It is upon the breeder to choose a system that meets his requirements. The system of record keeping should be as simple as possible. Pedigrees can be filed in book form, on index cards, or in some type of computerized system. Some simple accession number system which includes the year in which the material was grown will enable the breeder to check pedigrees when desired and this reduces the time and errors that might result from listing long pedigrees.

Many plant breeders use a two-digit number denoting the year, followed by a three digit cross number. This may be preceded by the letter(s) denoting location. In the pedigree system, for example, MM85049(D x G) indicates cross number 49 made at Mount Makulu in 1985, with D as the female and G as the male parent. As generations are advanced in this pedigree

Regional Maize Course tor Technicians, Arusha, Tanzania June 1997 - Page 13

system, a selection number (the plant order in the nursery row) is added in each generation. Thus MM85049-3-9-6 denotes selfed seed from an F3 plant (nwnber 6) which resulted from selfed progeny of plant number 9 in an F2 row grown the previous year, which, in turn, resulted from selfed progeny of plant number 3 in an F 1 row.

2.6. Storage of seed after harvest

Seed is the carrier of the genetic potential for higher and sustained crop production. Proper storage of seed (in particular breeding material and gerrnplasm) is therefore of paramount importance in order to protect and to conserve this valuable resource for the benefit and survival of mankind. Following harvest and treatment of seed with the necessary pesticides, storage of seed is an activity which must be well planned and executed.

In the absence of adequate and proper storage facilities, serious losses may occur while seed stocks are held under storage between harvest and the next planting. The risk is even greater for stocks held in reserve for long periods of time.

The viability of seed in storage is a function of the relationship between seed moisture content, relative humidity and temperature. High temperature and high relative humidity lower seed viability very rapidly and favor storage insects. In areas where the temperature and relative humidity are high, seed can lose its viability within weeks.

2.6.1. Seed storage conditions

Lowering the moisture content of seed, and lowering the temperature and relative humidity in which seed is stored, will extend the storage life of most seed. The moisture content of seed is directly afiected by the relative humidity of the atmosphere around it. Raising the relative humidity increases the seed moisture percentage; lowering the relative humidity reduces the moisture percentage of seed.

2.6.2. Requirements for seed storage

The requirements for seed storage facilities will differ among crop research and development programs, however, most of them will need facilities for short-term, intermediate and long term storage. Table 2.1 shows the types of seed storage needs that may be required by the various components of the seed industry.


Table 2.1. Seed storage needs for various components ofthe seed industry

Activity

Crop research and development

Initial seed mcrease

Seed enterprises

Marketing agencies

Short term (6-8 months)

Breeding materials selected for current season's planting

Breeder and Basic seed for current season

Seed held from harvest through processing to distribution in current season

Seed ready for sale

Intermediate (8-20 months)

Breeding materials held in reserve

Reserve breeder and basic seed and unused supplies

Reserve seed and unused supplies

Unused supplies

Long term (3 years or more)

Gennplasm

Breeder seed of selected varieties, basic seed of inbred lines, and special lots of some varieties

Not nom1ally necessary unless a research program is supported

Not normally needed

Under long tenn storage, both temperature and humidity must be controlled. Research has indicated that seed should be dried to 11% moisture content, or lower, before being placed in storage. Storage in sealed containers has been shown to increase longevity of seed under storage. A rule of thumb has been established for maize seed storage and that is, to maintain a temperature (C) and a humidity so that the sum of the two values does not exceed 60. For example seed could be stored at a temperature of 1 0°C and 45 to 50% relative humidity. Under these conditions, and if constantly maintained, satisfactory gem1ination may be retained for up to 20 years.

3. BASIC CONCEPTS OF TRIAL MANAGEMENT

Zubeda Mduruma and Herman Akonaay

3.1. Introduction

Testing is needed when it is intended to introduce an unknown factor in an existing production system in order to determine its effects. In Agriculture, experiments which include environmental modification, variety trials, and improved cultural practices are important. Field testing of varieties, through appropriate principles of statistical design, proper trial management and data elaboration is the only scientific and universally recognised means for evaluating and identifying superior crop varieties.

Some basic concepts which will be utilised need defining:

• Treatments: Different factors, the effects of which are gomg to be measured or compared in tl1e experiment e.g. varieties.

• Experimental unit: The unit to which a treatment is applied i.e. experimental plot.


• Replicate: When a given treatment is applied to more than one experimental plot.

• Blocks: Groups of plots or experimental units.

3.2. Statistical design

Statistical design is the term given to the systems used to assign treatments to experimental plots. Statistical design takes into account the control, the main sources of variation in field testing, i.e. soil heterogeneity and also provides a systematic method of assessing experimental error. The design also provides for the possibility of making significant tests and comparison between treatments.

The experimental layout most frequently used can be classified into 3 groups:

• Complete blocks: all treatments are included in each block and blocks coincide with replications.

• Incomplete blocks: Treatments are not all included in the same block. Each block includes a subset of the treatments and the experiment is in a different form. Each replication includes a set of blocks and normally all varieties.

• Split plot: The plot is subdivided into subplots.

3.2.1. Randomized complete block designs (RCBD)

In this design the treatments are assigned at random in some groups called "Blocks". Each block is also assigned at random (Fig. 3.1 below).


~a~-- b l~ __ l d I e] Rep 1

l-;j~ a e I~ Rep2

ld a I e I c Li Rep3

Fig. 3.1. Model of a scheme with 5 varieties and 3 replications

3.2.2. Lattices

When it is necessary to compare a relatively large number of varieties (> 25) as m population improvement it is necessary to have incomplete blocks.

3 .2.2.1. Simple balanced lattice

The number of treatments or varieties has to be a perfect square (N\ Plots inside each replication are grouped in an NxN plot square and the number of replications will beN+ 1.

Advantage: It has a greater precision because it corrects soil heterogeneity in two directions at right angles.

Disadvantages: Excessive rigidness requiring the number of varieties to be a perfect square. It makes the random distribution of treatments complicated.


Block 1 2 3 4

1st Replication 2nd Replication 3rct R 1" . ~e_E_2catwn ----

1 . 5 9 . 13 5. 1. 2. .,

4 9 1 . 1 1 16 6 .)

2. 6 10. 14 6. 6. 5. 8 7 10. 12 2 5 .15 .,

7 11 . 15 7. 11 .12. 9 .1 0 11. 14 8. 3 9 .).

4. 8 12. 16 8. 16.15 .14 .13 12. 7. 13 10. 4

4th R r · ep 1cat1on 5th R r · ep 1cat1on

13. 1 . 7. 12. 14 14. 8. 2. 13 . 11 15. 10 .16. 3. 5 16. 15. 9. 6. 4

Varieties: 4 x 4 = 16: 1 to 16 Blocks : 1 to 20 Replication : 4 + 1 = 5 Basic plots : 1 to 80 = 80

17. 1 10. 15 . 8 18. 9 2. 7. 16 19. 13 6.

., 12 .).

20. 5 14. 11. 4

Fig. 3.2. Scheme for 16 varieties (4 x 4 lattice)


3.2.2.2. Partially balanced lattice

This is a design of incomplete blocks similar to the above in which the number of varieties has to be a perfect square (N2

). However, the number of replications is non-obligatory.

Advantage: Greater flexibility regarding replications. Disadvantage: Less precise regarding error estimate but it is still sufficient in most of the cases.

1 . 2. ,.,

4 .)

Rep 1 5. 6 . 7 8 9. 10 .11 12 13 .14 .15 16

T. ). 9 . 13 Rep 2 2. 6. 10. 14

,., 7. 1 1 . 15 .).

4. 8. 12. 16

1 . 6. 11 . 16 Rep 3 5. 2. 15 . 12

9. 14 ,., 8 . .)

13 10 7 4

Varieties 4x4 =16 Blocks 1 to 12 = 12 Replications 1 to 3 = 3 Basic plots 16 X 3 = 48

Fig. 3.3. Scheme for 16 varieties and 3 replications:

3.3. Size and type of plots

• The size of the plot refers to the entire plot and not just to the part to be harvested which is named "useful plot" (net plot). The form of the plot refers to the relation between its length and width.

• Plots which are too small may give results which are unrealistic; on the other hand, plots which are too large increase the distorting effect of soil heterogeneity. Large plots permit a greater influence of edge effects.

• Shapes of plots may vary from square to rectangular. Rectangular shapes which facilitate cultural operations are preferred when the soil of the site is variable and has strips with marked fertility differences. It is advisable to adopt large rectangular plots, placed with their longer dimension perpendicular to the strips.

3.4. Distribution and orientation of blocks and plots.

• In order to minimise experimental error, it is necessary to select the most adequate layout and to apply the correct number of replications, distributing plots accordingly.

• Alleviate possible effects of soil heterogeneity, blocks which should occupy a minimum surface should be as homogeneous as possible. In any layout it is easy to

Regional Maize Course for Technicians. Arusha. Tanzania June 1997 - Page 19

eliminate differences between blocks but it is very difficult to eliminate differences arising from within the block.

• When the fertility level and its variation are known, blocks should be oriented in such a way as to minimise soil differences within each block even if differences between blocks may be high.

11 l 2 3

I t r I 6

I 71 Fertility gradient

r r 1'0 Ill 112 113 ! 141

Fig. 3.4. Fertility gradient

If there is a fertility gradient in a given direction, blocks should be arranged at right angles to the gradient, and plots should be narrow and long (Fig. 3.4).

When fertility variation is not known, use blocks as compact and as near to square as possible. This is because adjacent plots will probably be more similar than those that are further apart. Thus every source of variation has to be kept as far as possible within blocks.

• If it is impossible to complete a cultural operation e.g. irrigation or sowing in one day on the entire experiment, then the operation should be completed at least on all plots of a block.

• When the field is on a slope, blocks should be parallel to contours i.e. at right angles to the direction of the slope (Fig. 3.5).

Block 1

Contour

21 3~4IJ Block 2

Fig. 3.5. Blocking on countours

3.5. Edge Effects (border rows)

• Generally, growth and productivity of plants situated on the edge of a plot are different from those situated within the plot. In order to overcome border effects it is advisable to eliminate a strip around each plot. Great care should be taken to ensure that the remaining area is exactly the same in each plot, this is termed "useful plot" (net plot).


• Only use border rows when they are necessary. If non-planted alleys are present then it is necessary to have guard rows. If the alleys are part of the crop then decide whether crop responses being measured are affected or biased by neighboring plot areas. If not then there is no need to use guard areas as this affects overall trial size.

• The border area depends on the crop or variety under test. A tillering crop needs a larger border area.

• To decrease the variability in yield data fi·om farmer managed trials, you can have the whole plot, ignore border effects or share border rows between plots. This tactic should be used only with good judgement.

• Guard rows receive the same treatment as the harvested area (net plot).

3.6. Laying out trials

Although laying-out of a trial is a simple operation, it may cause problems if it is not carried out correctly and carefully. When selecting the site, several considerations should be made to make sure that the site is suitable for the trial. It is important to leave a margin around the basic plot in order to have space for work and allow for miscalculation of plot size. In addition, it is essential to consider the following factors:

• Site history, years in cultivation previous crop and management practices.

• Topography and soil-determine slope, aspect, soil depth, surface texture etc. • State of site at planting - decide if crop residues are present, weed burden, wet or dry

seed bed. • Rainfall data - it is useful to have a rain gauge at each site particularly if too little or too

much rain is likely or if its distribution may present difficulties. Rainfall data are vital to the interpretation of treatment responses or lack of them.

Before you visit a site to lay-out a trial, prepare the following:

• Have a description plan for the site. • Pegs, sisal twine and labels • Tape measure.

Procedure:

• Start marking out from the lower right hand corner, following the direction of sowing.

• Take the right angle boundaries of the trial using a tape measure and mark the boundaries of the trial with pegs, sighting the additional pegs for the individual plots.

More permanent pegs are required for long term trials to avoid shifting of plots. Considering the row as one side or leg of a right angled triangle, a right (90°) angle should be constructed at the corner. A Pythagoras triangle (Figure 3.6 below), with sides measuring 6, 8 and I Om long will produce right angled plots. The 6m side is marked along the row, 8m side across the rows and the I Om side is the hypotenuse. The direction of the side across the rows will be the base line for the experimental plots. Place pegs at the corner of each block of plots, leaving I or 2 unplanted rows between experiments and either 1 or 2m alleys between blocks.


6m

8m

Fig. 3.6. Pythagorous Triangle for Constructing Right Angles in the Field

3.6.1. Marking the Individual Experiments

It is crucial to be systematic in the numbering of plots. The most common procedure for numbering plots is to always start from left to right when facing the replication and numbering successive replications in a "serpentine" fashion (Fig. 3.7).

~7 I 26 I 25 I 24 I 23 ~ narrow alley

I '--15 _ _,_1 _16--'--17--'--l-18_1_~9-.l.-2-0-.L--2-1 wide alley

8

narrow alley

4 5 6

Fig. 3. 7. "Serpentine" way of marking plots

3. 7. Plot size

The plot size is determined by the objective of the trial, the experimental factors, the type of management and the measurements needed. Hence, the plot size is usually indicated in the field book of each trial.

• Plots should be large enough to give a good estimate of yield. Use larger plots for verification or demonstration trials, or trials involving tillage operations. Trials that explore a range of technologies need smaller plots sizes.


Example: Variety trials may have 5m x 5m plots while verification trials may have 1Om x 1Om or 20m x 20m plot sizes.

• In on-farm trials, larger plots permit farmer management levels to be realistically implemented and can help the researcher to identify resource conflicts. Many management problems do not manifest themselves on small plots.

3.7.1. Alleyways

Alleyways are a common component of field trials both on-station and on-farm because:

• Alleyways allow easier access to the inside of a trial for applying treatments and collecting data.

• Alleyways add some flexibility on the overall size of a trial. You can reduce the area allocated to alleys to limit the trial area.

• Alleyways may be necessary for trials with tillage treatments in order to provide space for turning the tillage implements.

• Alleyways may be used as source of pests or diseases in trial designed to look at these aspects.

• Alleyways do not need to be open ground. They may be part of the crop. Alleys of this type may serve as control area e.g. non-weeded alleys in a weed control trial. This technique can be used to decrease the number of plots needed in the trial.

3.7.2. Labelling

The labelling, marking or numbering of each plot ensures that data are collected from the correct plots. Each plot has to be marked or numbered in a standard system and an individual label for each plot.

3. 7.3 Planting

If planting is by hand, labelling will be carried out before planting, placing the label with its number on the first row of the plot. The pegs with labels should be firmly placed in the ground. It is better to have a field plan also recorded in the field book. The collection of data must not start until the plots have been adequately marked otherwise errors will occur and more time is required to make checks.

In order to realise full expression of yield potential and other agronomic characteristics the trial should be sown at optimum density. The plant density of 53,000 plants per hectare is being used at many sites as an optimum one. The materials are grown on 5 meter long plots at a row-to-row spacing of 75 em and hill-to-hill spacing within rows of 50 em. If between row spacing other than 75 em is used then a different within row spacing should be used but an optimum density of 53,000 plants per hectare should be maintained. Below is a table showing how this could be achieved.


Table 3.1. Dimensions for obtaining a density of 53,000 plants per hectare.

Row to row With 1 Plant/Hill With 2 plants/Hill Distance (em)

Hill to Hill Row length(m) Hill to Hill Row length(m) distance (em) (for 22 plants) Distance (em) (for 22 plants

65 29 6.09 58 5.8

70 27 5.67 54 5.4

75 25 5.25 50 5.0

80 24 5.04 48 4.8

85 22 4.62 44 4.4

90 21 4.41 42 4.2

95 20 4.20 40 4.0

100 19 3.99 38 3.8

3.8. Uniformity in managing trials

The best results are obtained from trials planted on fields that have uniform soil and are far away from trees. For large trials like 16 x 16 lattice experiments, well chosen fields are a necessity even though the effect of soil variation on the results are much reduced by a chosen design and good field layout.

3.8.1. Managing the application of treatments

• Often experimental treatments have to be applied at a particular moment in time or at a particular stage of crop development. Trying to make sure that a treatment is applied at the time given in the experimental description can sometimes present difficulties. The researcher may not be able to get around to all sites at the right time. He may not get information concerning relevant conditions fast enough.

• Take the likelihood of such occurrences into account when deciding on trial location and the number of sites. If you can arrange specific planting dates tor trials and stick to them, this will help in organising a schedule for the application of treatments. In practice, it may be difficult to do this because of weather, or unavailability of equipment or animals, but try. Confusion in the field at planting time can be avoided if inputs and equipment required to conduct the trial are assembled ahead of time.

• Have someone double check that all eventualities have been accounted for before you go to the field.

• Apply treatments systematically whenever possible, usually block by block. In some cases it may be more convenient to apply treatment by treatment to the whole trial e.g. when applying a few different spray formulations, but this method needs careful planning and always keep an eye open for rain.


•

•

•

•

•

•

Always work from a plot plan when applying treatments. Do not just work from labels on plot stakes, labels may be incorrect or the stakes may have been moved. Nevertheless, you can use plot labels as an additional check.

Use strong packets or plastic bags for treatments such as seed or fertiliser. Prepare them at the station or office when possible. This will save valuable time in the field at planting and will cut down errors. Organise the inputs on a per plot or per row basis. Volumes can be calculated for liquids so that preparation in the field is rapid using a graduated cylinder. Color-coded stakes are useful for marking plots that will receive different herbicides, etc. Delineate plots for long-term experiments with firm stakes and take careful notes of their exact location in the field.

Knapsack sprayers, and any other mechanical equipment should be tested for proper functioning and properly calibrated before going into the field. Do not rely on equipment being in good shape just because it was the last time you used it. Containers should be organised to carry all bulk inputs to the field. Plastic buckets with lids are good for bulk fertiliser and seeds. They protect the inputs in the field when rainstorms come suddenly and they prevent spillage in transit. Paper bags and open containers can be disastrous for spillage and in the rain.

It must be emphasized that:"It pays to make a checklist of items needed for the field on a particular visit for the particular trial and operation being carried out".

Remember to plan for the inputs and equipment needed to apply the non-experimental variables as well as the experimental treatments.

Decide beforehand exactly how the levels of the experimental variables will be applied . Make sure you know the variety of the crop, the source of seed, the dosage of a pesticide expressed as the rate of active ingredient and expressed as rate of commercial product on a hectare and per plot basis, the method of application, and the timing of application.

Please note that, a 10% extra of chemicals should be added to the amounts of chemicals prepared for application to allow for spillage, etc.

The researcher should take extra care when applying powders or granules (e.g. fertilisers) broadcast by hand. He may not be familiar with the rate of application and so not apply the same amount to all parts of a plot. If the plot is large, say above 20 square meters, divide it into sub-units, divide the material too and apply one portion to each sub-unit. If you cannot weigh the material in the laboratory then maintain it as a bulk and use volumetric measure e.g. a calibrated tin can or jar cap. These are especially useful for applying the product in banded form along a row or to hills.

To minimise plot size and plant density errors with animal-drawn furrows use marker sticks placed at each end of a plot or a trial to guide the worker.

In verification or demonstration trials (usually farmer managed) try to represent conditions under which a farmer would have to apply a treatment. For example, if you are treating seed with a fungicide then get the farmer to do the treatment in a bucket in the field, do not do it under controlled laboratory conditions.

Thinning to a stand is a common practice in on-station trials, this practice may be extended to "researcher managed" on-farm trials. However, farmers rarely do this, even in widely spaced crops like maize.


Triple check the dimensions of plots. It is easy to make say a 50 em error, but it is difficult to detect it visually, except in very small plots. A common problem among inexperienced trial assistants working with row crops is difficulty encountered in marking out plot areas and borders between plots. Errors in calculating harvest area can have serious consequences ifthey go undetected.

One last rule, worth stressing again - get someone else to recheck the lay-out, packets, etc. before you plant or apply experimental treatments.

3.9. Types of competition effects in field trials

Competition effects can be very large in small plot tield trials and can have implications on plot size and shape, harvested area, and on how to handle certain experimental treatments. Here we will look at some sources of competition that are associated with the trial itself and the design used and that can alter observed responses. Be on the lookout for these when you design and implement trials.

Plant competition may occur for space, water, mineral nutrients, light, oxygen and carbon dioxide. We will not look at competition between plants within a plot as induced by experimental treatment, for example, as may occur with blends of crop varieties, with intercropping of two or more species, with plant density or plant spatial arrangements, or that may be characteristic of the site but not associated with the trial e.g. competition for water, mineral nutrients or competition from weeds.

3.9.1. Non-planted borders

These are areas between plots or around trials that are left without plants and serve as markers or walkways. Such areas ar~ generally wider than the area between rows or between plants in a row, and so plants adjacent to the non-planted border have relatively more space. These plants are therefore exposed to less competition than plants in the center of the plot and so grow better. However, in some instances the border may contain more weeds than the body of the plot and therefore otTer more competition with the crop, reducing the growth and yield of plants in the border rows. Because of the uncertainty about the validity of response from border-row plants these plants are not normally harvested.

3.9.2. Varietal competition

In trials involving different varieties of a crop the adjacent plots are planted to different varieties. Varieties generally differ in their ability to compete for nutrients and water and so plants in a plot can be subjected to different environments depending upon their location relative to adjacent plots. The plants affected are the ones near the perimeter of a plot. The largest effects come when varieties differ greatly in physical characters like plant height, canopy spreading ability, foliage density and root distribution. The disadvantage of one plot is usually accompanied by a corresponding advantage to the adjacent plot. Again nonharvested border rows are used to remove this efiect from results. However, be careful, you may need to leave two rows of a crop to ensure no bias.

3.9.3. Fertiliser Competition

The effect of fertiliser competition is similar to varietal competition. In this case adjacent plots receive different levels of fertiliser which may greatly afiect crop growth. Here the competition effect has two sources:


• Plots with larger fertiliser application will be more vigorous and can probably compete better for radiation and carbon dioxide.

• Fertiliser could spread to the root zone of adjacent plots, putting the plot with higher fertiliser at a disadvantage.

In most cases the effect of fertiliser dispersion is larger than that due to differences in plant vigor. The net advantage is usually with the plot receiving the lower fertiliser rate.

3.9.4. Missing hills

A missing hill causes the plant surrounding its position to be exposed to less competition than other plants in the plot. These plants, therefore, usually perform better than those completely surrounded by living plants. In on-station trials with crops like maize we commonly get around this by over-planting and then thinning to a near perfect stand. There are also standard ways of compensating for missing hills by selective thinning of a crop, but these are rarely used in on-farm trials, especially those that are farmer managed.

3.10. Data collection in maize trials

Experiments are planted in order to test one or more carefully chosen hypotheses. To make these tests we need to obtain information or data from the experiment. The collection of these relevant data, completely, accurately and efficiently is the most important activity during the experimental phase of on-station and on-farm research.

3. 1 0 .1. Why collect data in experiments?

Data are collected in experiments in order to:

• Measure the effects oftreatme11ts and decide ifthe treatment effects are real. • Interpret the performance of the experimental treatments in trials. • Determine if promising treatment effects are economic and so likely to be adopted

by farmers.

3.1 0.2. Types of data collected

The type and amount of data we collect during experimentation will depend on the types of hypotheses being tested, on the manpower and expertise available and on the equipment at our disposal.

Guidelines on how to go about deciding what data to collect and what to leave out are difficult to put on paper but such decisions are important as they determine the success of a research program. Plan the analysis and likely interpretation before hand to decide the data needed. Collect as much information as you can on performance aspects of treatments as well as on farmers practices and preferences for on-farm trials. Economic yield alone is widely enough except in verification or demonstration type trials.

Remember, do not over stretch yourself because the quality of data is more important than the quantity.

Plant Stand Count

Record the number of plants in the net plot at the 3 leaf stage (about 15 - 21 days after planting (DAP)) for stand establishment. Early plant stand count is particularly useful when certain viral diseases or downy mildew are present. In trials where extra seeds were planted, early plant stand should be recorded after thinning. In most cases, however, plant stand is recorded at the time of harvest for yield determination

Regional Maize Course for Technicians. Arusha. Tanzania June 1997- Page 27

Days to 50% PoJien Shed (Anthesis)

Record the number of days from planting until the date on which 50% of the plants in a plot have shed pollen.

Days to silking

Record the number of days from planting until the date on which 50% of the plants in a plot have silks 2-3 cmlong.

Plant height

For 10 plants selected at random measure the distance from the plant base to the point where the tassel starts to branch. Record the plant height in centimeters. Alternatively you may estimate this distance for each plot using a measuring rod. Plant and ear heights can be measured 2-3 weeks after flowering or just prior to harvest, depending on working schedule.

Ear Height

For the same 10 plants whose height you have measured also determine the distance from the plant base to the node bearing the uppermost ear. You can also estimate the distance for each plot using a measuring rod.

Root Lodging

Data on root and stalk lodging must be taken late in the season just before harvest. Record the number of plants that are leaning 30° or more from the perpendicular at the base of the plant where the root zone starts.

Stalk lodging

Record the number of plants with stalks broken below the ears but not above the ears. There may be some weak plants that have poor stalk quality, but which have not yet lodged. To identify these push the stalks gently and plants which then fall over should be counted as stalk-lodged plants. The data on stalk and root lodging are entered separately since a particular plant might be both root lodged (leaning more than 30°) and stalk lodged (broken below the ear).

Husk cover

Before harvest record the number of ears in each plot that have any portion of the ear exposed. This figure will be converted into a percentage of poor husk cover by dividing it by the total number of cars harvested. Also, for each plot rate materials for husk cover on the 1-to-5 scale described below. Score entries on this trait when ears are fully developed and the husk is drying down. The best time is 1-3 weeks before harvest.

Rating scale

I. Excellent 2. Fair 3. Exposed tip 4. Grain exposed

5. Completely unacceptable

Husk cover

Husk tightly covers ear tip and extends beyond it. Covers ear tip tightly. Loosely covers ear up to its tip. Husk leaves do not cover the ear adequately, leaving its tip somewhat exposed. Poor husk cover, tips clearly exposed.


Total number of ears

Record the total number of ears harvested, excluding secondary ears that are extremely small.

Rotten ears (Diseased Ears)

For every plot rate the incidence of ear and kernel rots caused by Diplodia .~pp., Fusarium spp. or Gibberella spp. on a scale of 1 to 5, as follows.

1. 0% infected kernels 2. 10% infected kernels 3. 20% infected kernels 4. 30% infected kernels 5. 40% or more infected kernels

Ear aspect

After harvest, but before taking a sample for moisture determination, spread out the pile of ears in front of the plot and rate them for characteristics such as disease and insect damage, ear size, grain filling, and uniformity of ears on a scale of 1 to 5, where 1 is the best and 5 the poorest. Record these ratings in whole numbers in the column headed "ER ASP".

3.11. Harvesting maize trials

If possible, delay harvesting of maize trials until grain moisture is low ( 15-25% ). This will allow full expression of stalk and root lodging. In addition the grain is much easier to shell for moisture content determination and moisture meters are more accurate at low moisture.

Yield or production data are fundamental in a comparative trial of varieties. Vegetative, qualitative, technological and other data are also important and give invaluable information but they are always complementary to yield data and are used for better understanding of the results. It is therefore important that the greatest attention and care is given to harvesting and post harvest operations because any error, even insignificant, may seriously affect the results. The sizes of the plots are generally very small and an error of a few grams will be reflected as several kg/ha.

The first decision regarding harvesting is the date on which to be done. Generally, a trial has to be harvested as soon as the required maturity stage has been reached.

It is advisable to prepare all necessary items of equipment well before the harvest date. This should include labels, string, bags for collection of samples and items for later tests (quality and so on), balances, moisture meters, sacks etc.

Follow the instructions given in the individual field books.

Maize trials are normally harvested by hand. The actual trial plot area will be marked inside each elementary plot, taking into account the perimeter areas which will be discarded. In a 4-row plot trial, only the 2 middle rows will be harvested.

The guard rows are harvested and the material taken outside the field to avoid confusion before harvesting the trial plot.

Sometimes the trial area is harvested before the guard rows as long as it is properly marked. The crop in each plot is harvested, put in bags marking the material from each plot with a numbered label, corresponding with the plot and replication; labels should also indicate the total number of lots originating from each plot.


Crop weighing and moisture determinations should be done during harvesting. The balance and moisture meter should be put in a suitable place to which sacks are brought. The responsible person will do the weighing as well as other determinations which are noted immediately in the field book.

3.12. Determination of grain yield in maize

Suppose you are given that:

Y = Maize Grain Yield in kg based at 15% Moisture Content.

FWP =Field Weight of maize in a net plot/Harvest area (5.45 kg).

DM =Fraction of dry matter in a sample which is expressed as:

Dry weight of Sub-sample = (1.320) = (0. 719)

Fresh wt of Sub-sample ( 1.836)

S = Shelling % expressed as fraction: = Grain wt (1.098) = (0.832) Ear wt (1.320) both after drying.

M = Moisture factor 1 00 = (1.176) for 15% Moisture 85 content.

F = Conversion Factor from kg/plot to kg/ha = 1 OOOOm~ = 10000 = (1388.9) Harvest area 7.2

Grain Yield (Y) = FWP x DM x S x M x F

If you substitute the values in brackets then:

Yield of Grain (Y) = 5.45 x 0.719 x 0.832 x 1.176 x 1388.9

Y = 5325 Kg/ha of grain at 15% moisture

Regional Maize Course for Technicians, Arusha, Tanzania June I 997- Page 30

3.13. Field diary

Describe order of operations performed and record their dates as shown in the following operation sheet.

Trial. ................................. . Site: ...................... . Altitude ........................... .

Collaborating Institution Collaborator

Rainfall for cropping season ....................................................... .

Dates of::

Ploughing .................................................... .

Harrowing: ................................................... .

Ridging: ..................................................... .

N application at Planting: ........................ . Side dressing: ............................................... .

P application: ............................................... .

Planting ..................................................... .

Weeding: ..................................................... .

Herbicide Application: ....................................... .

Last Rain before Application: ................................ .

First Rain after Application: ................................ .

Gern1inated: .................................................. .

·rhinning: .................................................... .

Flowering started: ........................................... .

insecticide treatment 1st.. .................................. .

2nd: ......................................................... .

Maturity: .................................................... .

Harvest: ..................................................... .


3.14. References

F.A.O. 1993. Technical Guidelines for field variety trials Eds. Elena Rossello J.M and M. F ernardez Gorostiza.

Fehr, W.R .. 1987. Principles of cultivar Development Vol. 1. Theory and Technique McGraw-Hill Inc.

Gardner, C.O. 1961. An evaluation ofthe effects of mass selection and seed irradiation with thermal neutrons in a field of com. Crop Sci. 1: 241 - 245.

Lmmquist, J.H. 1964. Modification of the ear-to-row procedure for the improvement of maize populations. Crop Sci. 4: 227-228.

4. PRINCIPLES OF PLANT BREEDING

Batson Zambezi

4.1. Introduction

Among the world's cereal crops, maize ranks second to wheat in production, with milled rice third (Dowswell et al., 1996). However, among the developing economies, maize ranks first in Latin America and Africa but third after rice and wheat in Asia. Seventy countries, including 53 developing countries, plant maize on more than 100,000 hectares. The farreaching distribution of maize production is an indication of its excellent capacity to adapt to many environments. Maize is grown at latitudes varying from the equator to slightly above 50°, from sea level to over 3000 meters elevation, under heavy rainfall and in semiarid conditions, in cool and very hot environments, and with growing cycles ranging from 3 to 13 months.

Five hundred million tons of maize are produced annually on 130 million hectares. Sixtyfour percent of the world's maize area is found in developing countries, even though only 43% of world production is harvested there. The difference between the industrialized and developing countries is striking. The average for industrialized countries is 6.2 t!ha, compared with 2.5 t/ha for developing countries. This difference is due to environmental, technological, and organizational factors.

4.2. Importance of maize in the SADC Region

The trend of maize production for the past 20 years for eight SADC member states : Angola, Lesotho, Malawi, Mozambique, Swaziland, Tanzania, Zambia and Zimbabwe, shows a gradual increase of maize grain from 7 million tons in 1976 to a peak of 9 million tons in the 1988/89 season. Production fell drastically to the lowest of 4 million tons in the 1991/92 drought year.

Maize is the most important food crop in the region, accounting for, on average, over 40% (when Eastern Africa is excluded) and over 15% (when Eastern Africa is included) of the total calories in people's diets (Dowswell, et al., 1996). The population of the original nine SADC member states was just over 81 million in 1991, with an average growth rate of3%, which is high (Table 4.1). Thus, the need for increased food production in order to feed the escalating population cannot be overemphasized.

Worldwide, 14% of the maize crop is processed industrially for food, feed, and non-food uses (Dowswell, et al., 1996). The most elaborate and diversified uses of maize occur in the


United States where, in 1991, about 34 million tons of maize (19% of national production) were used for industrial purposes and seed processing. Wet-milling of maize for starch and sweetener manufacture consumed 20 million tons. Three-quarters of this amount was for sweeteners, primarily for soft drinks. Maize was also an important raw material for ethanol fuel production.

4.4. Types of maize

Based on kernel appearance and texture, Sturtevant (1899) classified maize into the following sub-species or types: (i) Flint maize (Zea mays indurata Sturt); (ii) Dent maize (Zea mc~ys indentata Sturt.); (iii) Sweet maize (Zea mcrys saccharata Sturt.). (iv) Pop maize (Zea mays averta Sturt.); (v) Floury maize (Zea mays amylacea Sturt.); and (vi) Pod maize (Zea mays tunicata Sturt.). However, this classification was revised as follows by Grebencsikov (1949), who introduced the term con-varieties (varietal groups) to designate the maize types.

4.4.1. Flint maize- Kernels have a small portion of soft starch which is surrounded all over by hard starch, giving it a smooth, shiny and generally round shape. Flints are widely grown and preferred for food uses in Asia, Europe, Central and South America. In view of the relatively hard endosperm, flints have better storage capability.

4.4.2. Dent maize- The hard starch is on the side of the kernel, while the soft starch extends on the crown or tip of the kernel. On drying, the soft starch loses moisture rapidly and shrinks more than the hard starch to form a depression or dent at the crown. The kernels are relatively long and thin. Dent hybrids are popular in the USA, parts of Europe, Zimbabwe and Zambia. SR52, MM752 and MH12 are good examples of a dent hybrid.

4.4.3. Sweet maize - Mature kernels are wrinkled, transparent while immature kernels have high proportion of sugar to starch. This character is determined by a single recessive gene.

4.4.4. Pop corn (maize) - Kernels are small. The proportion of soft starch in relation to hard starch is much smaller than that of f1int maize. Kernels with optimum moisture level readily pop upon heating in oil.

4.4.5. Floury maize - The endosperm is made up of soft starch except for a thin lining of hard starch on the side and there is no dent (depression) in the crown.

4.4.6. Pod maize - Individual kernels are enclosed in a pod or husk and like in other types the entire ear is also covered by husk leaves. The endosperm of the kernel may be flint, dent, pop, sweet or waxy. Typical types of pod maize are heterozygous and are not being grown commercially.

4.5. Food uses maize

More than half of all maize is utilized directly as human food the Andean countries of South America, Africa, and South and Southeast Asia. Maize accounted for at least 15% of the total daily calories in the diets of people in 23 developing countries, nearly all in Africa and Latin America. Maize is consumed in the form of a thick porridge called "Ugari" in Tanzania, "Sadza" in Zimbabwe, "Nshima" in Zan1bia and "Nsima" in Malawi. The processing of maize grain into flower varies from country to country. In Malawi, for instance, maize grain is pounded in a mortar with a pestle to remove the pericarp, after which the polished grain is soaked for a couple of days. The grain is then dried and milled into flour. This kind of processing produces very white and fine flour, which makes the


nsima soft and more palatable, as compared to whole grain milled flower "mgaiwa". Secondly, this type of processing needs grain that is hard in texture (endosperm hardness), so that there is minimal breakage during the pounding process. This is why flint maize is more preferred Malawi to dent maize. The other reason is that flint maize tends to store better than dent maize. Other countries such as Zimbabwe and to some extent Zambia prefer dent maize, probably because it is easier for industrial milling to produce 'milie meal' which is very common in the urban centers of the two countries.

4.6. What is plant breeding?

Plant breeding is the art and the science of changing and improving the heredity of plants (Poehlman and Borthakur, 1969). In earlier days the extent of plant breeding as an art and as a science was much disputed. Plant breeding was first practiced when man learned to select the better plants; thus selection became the earliest method of plant breeding. The results of man's early efforts in plant selection no doubt contributed much to the course of development of many of the cultivated crops, however little he may have been conscious of his efforts in the beginning. The art of plant breeding lies in the ability of the breeder to observe in plants differences which may have economic value. Many breeders were good observers, quick to recognize between plants of the same species variations which could be used as the basis for establishing new varieties. For them plant breeding was largely an art (Poehlman and Borthakur, 1969).

4. 7. Objectives of maize improvement

In general, the objectives of maize improvement may include the following:

• Increased Productivity (Yield): improvement in the yield potential of the variety is one of the most important objective irrespective of the level of management and environmental conditions.

• Stability of Production: Stability of performance is as important as the improvement for the economic yield. The selected varieties should have the capability to withstand reasonably well the attack of important diseases and pests as well as minor f1uctuations in the environmental and crop management practices.

• Response to Production Inputs: Maize varieties differ in their response to various levels of production inputs, such as fertiliser, and irrigation water. It is, therefore, necessary to select varieties which will give optimum response to every unit of input.

• Tolerance to Soil and Environmental Stresses: The productivity of maize suffers when the crop is grown in problem soils (acidic, saline, alkaline) and stress environments (moisture stress, high temperature, and frost). Selection made under various constraint environments for higher productivity can be of considerable help.

• Improvement of Grain Quality: Grain quality has to be considered from two aspects: (i) the consumer acceptability of the grain type and color, and (ii) the nutritional quality. It is, however, desirable that the nutritionally superior types are comparable in productivity, stability and other agronomic traits with the traditional varieties. For instance in Malawi, Mozambique, Tanzania and to some extent, Zambia , smallholder farmers prefer white flint grain type to dent due to traditional processing and storage problems.

4.8. Role of Genetic Diversity in the development of maize hybrids


It will be desirable to initially identify specific pairs of populations which give high hybrid performance. Inbred lines from these populations in early and advanced generations, when crossed, are likely to give high yielding hybrids. If necessary, suitable broad based complementary heterotic populations may be specifically synthesized for this purpose. In a double-cross hybrid, the genetic diversity among the inbred lines has to be exploited at the final stage. This aspect has been well shown by the order of sequencing of the lines. Eckhards and Bryan (1940) showed that when inbred lines A and B were derived from one source population, and lines X and Y from another, the double-cross hybrid (AxB) x (Xx Y) out-yielded (AxY) x BxY) or (AxY) x (BxX). The precise sequencing of the lines in a double-cross hybrid will also be determined by the~ se performance of the parental lines.

4.9. Germplasm for special traits

Drought causes a 10-50% annual yield loss on 80% of the area planted to maize in southern Africa (Short and Edmeades, 1991 ). Of yield losses caused by drought, most losses are due to moisture stress occurring during t1owering of the crop (Edmeades et al., 1994). CIMMYT has focused on developing techniques for improvement of maize tolerance to drought occurring during flowering. Edmeades and coworkers have also shown that improvement for drought tolerance in Tuxpeno Sequia resulted in excellent performance under low N. Gains in yield under low N due to selection for drought tolerance averaged 13 5 kg/hal cycle. The advanced cycles of Tuxpeno Sequia and Pool 26 Sequia outyielded Co by 28% and 49%, respectively. These findings are encouraging.

In the CIMMYT -Zimbabwe Maize Program Population ZM 601 is undergoing improvement for drought tolerance (Pixley, personal communication). In addition, Tuxpeno Sequia has undergone two cycles of selection, adapting it to Zimbabwe conditions. It has now much better drought tolerance, with , anthesis-to-silking interval (ASI) similar to ZM 601. There are a number of materials that are being screened for drought tolerance in drought prone sites, Makoholi and Matopos (Zimbabwe). Two populations, Drought A and Drought B, were developed by Kent Short with emphasis on drought tolerance. The materials that went into the two populations were mostly selected for good performance in drought environments. These include K64R, and some versions of N3 and SC that were found to be heat tolerant (Pixley, personal communication).

CIMMYT has established a project for breeding drought tolerant maize in the region. The project is based at the CIMMYT-Harare Station in Zimbabwe and is coordinated by Marianne Banziger. This project is coming at an opportune time. Countries in the region have limited resources (human, financial and material) to effectively tackle this problem. It is hoped that the project will have a significant impact on maize production in the region ..


4.9. References

CIMMYT. 1994. CIMMYT 1993/94 World Maize Facts and Trends. Maize seed industries, revisited: Emerging roles ofthe public and private sectors. Mexico, D.F.: CIMMYT.

Dowswell, C.R., R.L. Paliwal, and R.P. Cantrell. 1996. Maize in the Third World. Westview Press. Inc., Colorado, USA.

Edmeades, G.O., J. Bolanos M. Hernandez, and S. Bello. 1993. Crop physiology and metabolism. Causes of silk delay in a lowland tropical maize population. Crop Sci. 33: ] 029-1035.

SADC Regional Early Warning Unit Quarterly Reports. 1991-95. P.O. Box 4046, Harare, Zimbabwe.

Short, K.E., and G .0. Edmeades. 1991. Maize improvement for water and nitrogen deficient environments. In: J.F. MacRobert (ed.). Proceedings ofthe Crop Science Society of Zimbabwe Twenty First Anniversary Crop Production Congress. Harare, Zimbabwe.


5. POPULATION IMPROVEMENT

The first step in variety development is to form a population with genetic variability for the characters of interest. In genetics a population is a community of individuals that share a common gene pool. The populations used for cultivar development range from a two-parent cross to a complex population involving several parents. A population with several parents is advantageous because is has a wide genetic diversity hence potential transgressive segregants can be expected quite often.

5.1. Development of a two parent cross

Season Procedure

• Cross two parents obtain hybrid F 1 seed.

• Grow F 1 plants. Obtain F2 seed.

F 1 self pollinate

! F2 seed

5.2. Development of a Complex population

• Make two-way crosses between parents (first intermating).

Fl X Fl Fl X Fl

• Cross F 1 plants from different two-way crosses (Second intermating.

Fl X Fl

• Cross F 1 plants from different four-way crosses (3rd intermating)

Hybrid seed

l Plants of bulk population

Both diallel and partial diallel designs are commonly used to form a complex population. The matings may be accomplished by artificial hybridisation, open pollination or a combination of the two. A combination of the procedure is useful as it permits the greatest amount of recombination possible within resources available for hybridisation.

5.2.1. Diallel

Season 1:

Season 2:

Season 3:

A diallel without reciprocal crosses and self pollination is made to form [P(P-1) ]/2 single cross pollination. A partial diallel is used to intercross the single-cross populations formed in season 1.

Hybrid seeds from season 2 are bulked and planted as one population. A partial diallel consisting of plant to plant crosses is used for the 3 rd

generation ofintermating.


5.2.2. Partial diallel

Season 1:

Season 2:

A partial diallel is used to mate a large number of parents.

Hybrid Seed from season 1 planted as bulk in isolation. Natural hybridisation is used for the second generation of intermating.

Season 3: All subsequent generations of intermating conducted in the same manner as described for season 2.

Population Improvement provides for the cyclic upgrading of open pollinated varieties, synthetic varieties and inbred lines.

Reasons for forming and improving populations

• For use as source population for new inbred lines. • Used for direct selection of cultivar for use by farmers in areas that do not have means

for production, distribution and growing of hybrids. • Utilised in recurrent selection.

5.3. Methods of selection for population improvement

5.3 .1. Intra-population improvement • mass selection • half-sib selection • full-sib selection • selfed progeny selection

5.3.2. Interpopulation improvement

• Reciprocal half-sib selection • Reciprocal full-sib selection

The choice of any one method of selection depends on:

• Stage of the breeding program, • Stage of the germ plasm development, • Knowledge ofthe populations, • Objectives of the breeding program.

Available funds, facilities as well as objectives will determine the proportion of the effort a given maize breeding program will allot for population improvement.

5.3.3. Mass selection

• One of the oldest methods used in maize breeding.

• Refers to when individual female plants are selected after they have been pollinated by unselected males in the population.

• Ears of the selected plants are harvested, shelled and equal quantities of the selected seeds are bulked for planting in the following season.

• Effective for fixing traits that are not affected by environment, have high heritability. • Its effectiveness depends on the plant trait being improved, adequate isolation and

the precision of the experimental techniques used by the breeder.

5.3.4. Half-Sib (HS) selection


Effected by use of a common tester parent. The tester parent could be either the population that is undergoing improvement (intra), a population unrelated to the population under improvement (inter), narrow genetic base (inbred line) or a broad genetic base (any other open-pollinated variety, synthetic or composite variety). Most frequently used due to wide possible choices of tester.

Method - Individual plants in a population under selection crossed to common tester by hand pollination or in isolation plot where the tester is the male parent. Half-sib progenies i.e. all progenies that have a common parent are evaluated in replicated yield trials. The superior performing genotypes are identified. Remnant seed of the superior half-sib progenies is planted and recombined to form the next cycle of the population.

5.3.5. Ear-to-row

Ears from a population are planted ear-to-row and evaluated on a progeny-row basis. Selection unit in ear-to-row is the progeny i.e. a half sib family of an ear. Requires adequate isolation to prevent contamination from other varieties. A modified ear-to-row method was suggested by Lonquist (1964). The progeny rows are replicated in different environments- one which is isolated for recombination.

5.3.6. Full-sib (FS) selection

Effected by crosses in which progenies have the same two parents. Full sib progenies developed by crossing two individuals that are either in the same population (Intra) or in two separate populations (Inter). FS progenies are evaluated in replicated yield trials. Remnant seed of superior progenies is used for recombination to form the next cycle of the population.

5.3.7. Selfed progeny selection

This selection technique is not as extensively used as HS and FS selection techniques for population improvement. It includes evaluation of selfed progenies themselves determine superior progenies and recombine remnant seed of the selfed progenies to fonn the next cycle of the population. Generation of progenies to be evaluated usually is in S 1 or S2•

Advantages include increased variability among progenies evaluated and exposure of deleterious recessive genes that can be eliminated. Some of the disadvantages of this selection scheme include: longer cycle intervals but can be minimised using off-season nurseries; inbreeding effects if advanced generations are recombined.

5.3.8. Recurrent selection (RS)

Recurrent selection is broadly defined as the systematic selection of desirable individuals from a population followed by recombination of the selected individuals to form a new population, as illustrated below:

a). Formation of a base population b). Crossing within the population c. Segregation d). Selection of superior individuals e). Repetition in cycle fashion of steps b - d.

The base population is referred to as Cycle 0 (CO) population. The population formed after one cycle of selection is called cycle 1 (C 1 ); Cycle 2 (C2) population is developed from


second cycle of selection and so forth. The recurring population improvement system leads to the name "recurrent" selection.

5.3.8.1. Objective ofrecurrent selection.

To improve the performance of populations for one or more characters. The improved populations can be used as cultivars per se, as parents of a variety - cross hybrid and as a source of superior individuals that can be used as inbred lines, pure-line cultivars or parents of a synthetic. Successful recurrent selection results in an improved population that is superior to the original population in mean performance and in the mean performance of the best individuals within it. The improved population has a higher mean performance than original population (X0 ). It also contains individuals superior to those of original population.

5.3.8.2. Advantages ofRS

• It increases probabilities of recovering more favorable genes. • It tends to concentrate desirable alleles while maintaining vigor and genetic

recombination through outcrossing. • It minimises the loss of favorable genes in the population by accidental exclusion in

the selection process.

Select superior individuals as parents

Develop a population

Evaluate individuals in the population

Fig. 5.1. Cyclic process of recurrent selection

5.3.9. Methods oflntrapopulation Improvement in RS

5.3. 9.1 Recurrent Phenotypic Selection

Also referred to as mass selection or simple recurrent selection. Selection is based only on the female plant because the ear is pollinated by both selected and unselected plants. One of the earliest methods used to improve cross-pollinated crops. One of the problems with phenotypic selection of individual plants is the variability among plants caused by variations in soil type, fertility, moisture etc.


xxxx xxxx xxxx

xxxx xxxx xxxx

~ xxxx xxxx xxxx

Seed of cycle 0 population

xxxx I Population xxxx sub-divided xxxx into blocks

Superior plants in each block selected without regard for performance

Bulk of seed from selected plants - cycle 1 population

Fig. 5.2. Recurrent phenotypic selection

The effect of micro-environmental variability on recurrent phenotypic selection can be reduced by sub-dividing the population (cycle 0) of individual plants into blocks or a grid, selecting the superior individual within each block, and bulking the seed of selected individuals to form the new population (cycle 1) for the next cycle of selection (Gardner, 19961).

5.3.9.2. Recurrent half-sib selection

This involves the evaluation of individuals through the use of their half-sib progeny as shown below:

Cross plants being evaluated to a common tester.

• Evaluate the half-sib progeny of each plant • Intercross the selected individuals to form a new population.

Several alternative procedures exist depending on testers used, selection of one or both parents and the seed used for intercrossing.

5.3.9.3. Recurrent full-sib selection

This involves the testing of paired - plant crosses. It is the only method of recurrent selection in which the seeds from two individuals rather than one are used for testing and to form the new population.

Procedure

Season I:

Season 2:

Full-sib families are developed by making crosses between pairs of selected plants in a population (cycle 0). Part of the full-sib seed is put in storage for use in intermating selected full-sib families in season 3. The other part ofthe seed is used for testing in season 2.

The full-sib families are evaluated in replicated tests, superior families are selected.

Regional Maize Course for Technicians, Arusha, Tanzania June 1997 -Page 41

Season 3: Selected families are intercrossed (using full-sib seed). The harvested seed (Cycle 1) is used to begin the next cycle of selection).

Season 4 to 6 The second cycle of selection is conducted by repeating procedures for seasons 1 to 3. Subsequent cycles of selection are conducted in the same manner.

5.3.9.4. Recurrent Selection among selfed families

This is a method that involves testing of lines after one or more generations of selfing followed by intercrossing of individual lines to form the new population.

Procedure

Season 1:

Season 2:

Season 3:

Season 4:

S" plants from a population (Cycle 0) are self pollinated and harvested individually.

The selfed progenies are evaluated in replicated trials and the superior lines selected.

Remnant S 1 seed is used to intercross the selected lines. The seed obtained from the crosses represents the Cycle 1 population.

The procedure of Seasons 1 to 3 is used for each cycle of selection

5.3.10. Methods of interpopulation improvement

5.3.1 0 1. Reciprocal half-sib selection This is a method for the simultaneous improvement of two populations. Two segregating populations are selected, one designated A and the other B. Population A is used as a tester to evaluate individuals in Population B and vice versa.

Procedure

Season 1:

Season 2:

Season 3:

Season 4:

l 00 plants selected in population A (Cycle 0) are selfed and crossed to 6 or more random plants in population B and vice versa for selected plants in population B. The selfed seed of each plant is put in storage.

The 100 half-sib families of population A and the 100 from population B are evaluated in replicated trials. The top 10 half-sib families are selected from each population.

The 1 0 plants in population A that had superior HS progeny performance in season 2 are intercrossed to form a cycle 1 population using the selfed seed produced in season 1. The 10 plants in population B are treated in a similar manner.

Cycle 1 seed of populations A and B is used to conduct the next cycle of selection as that described for season 1 - 3.

5.3.11. Reciprocal full-sib selection

This is a method of interpopulation improvement that is used when the commercial product intended is hybrid seed. A cycle of selection is completed in the fewest number of seasons by the use of plants from which selfed and hybrid seed can be obtained.

Procedure


Season 1:

Season 2:

Season 3:

Season 4:

Two hundred phenotypically desirable S0 plants in population A (Cycle 0) are paired with 200 plants in population B (cycle 0). For each of the pairs, the plants are selfed and crossed to the other member of the pair.

The 200 Full-sib families are evaluated in replicated trials and the superior 10% are selected.

The selfed seed is used to intercross the 20 individuals of each population independently that were members of the 20 top full-sib families. The intercrossed seed of population A and B represent the cycle I populations.

The procedure used in seasons 1 to 3 is repeated to obtain the other subsequent cycles.

5.4. Formation of open pollinated maize varieties (OPV's)

Once a satisfactory level of improvement of the population has been achieved, the breeder may decide to form a variety. Progenies of a population are tested at different sites in targeted enviromnents. The best proportion of the progenies can be selected at each site and across sites for development of an experimental variety (EV). In addition to high yield, uniformity for maturity, plant and ear height are important considerations in the selection of the ten (1 0) best families so that the final variety is uniform in appearance. The new varieties are tested in on-station and on-farm variety trials to ascertain their superiority to current varieties before they are released for use by farmers.

Progeny Trial (selection of best families).

l Full sib recombination ofthe best families (F 1 ).

l Advance to F2 using Full or half-sib recombination.

E . lV J " . . 1 xpenmenta anet1es 10r vanety tna s.

5. Types of open pollinated varieties

A variety is a group of plants with characteristics that are distinct, uniform and stable. Distinct indicates that the variety can be differentiated by one or more identifiable morphological, physiological or other characteristics from all other known varieties. They are uniform because the variation among the plants of a variety for distinctive characteristics can be described. Stable indicates that the variety will remain unchanged reliably in its characteristics and its uniformity when produced or reconstituted. The terms variety and cultivar are considered equivalent, and are, sometimes used interchangeably.

Varieties of cross pollinated crops like maize are seldom developed from the offspring of a single plant. Usually the seed of a number of superior plants is composited and planted in an isolation plot to effect random mating for one or several generations. The harvest from such a plot becomes the foundation seed of the new variety.


5.5.1. Composite variety

A composite variety is a mixture of genotypes from several sources, maintained by normal pollination. When selection has been based on progeny tests and a group of progeny lines are composited, the procedure is termed "line breeding". In a composite variety, inbreeding is avoided by making sure that an adequate number of lines enter the composite and that these lines are not closely related.

5.5.2. Synthetic variety

This is a variety that is maintained from open pollinated seed following its synthesis by hybridisation in all combinations among a number of selected inbred lines or various other materials. The inbred lines forming the synthetic variety have first been tested for combining ability. Only those genotypes which combine well with each other in all combinations are put into a synthetic variety. The prior testing of hybrid performance distinguishes a synthetic variety from other open pollinated varieties. SYNO, SYN l, SYN2 etc. are symbols designating the original synthetic population, first synthetic generation (progeny of SynO), second synthetic generation (progeny of Syn 1), etc. Normally SYNI will have the highest yield performance because of maximum genetic diversity and hybrid vigor-expression. The SYN2 generation is somewhat low due to limited inbreeding depression. After SYN2 yield begins to stabilise and little reduction in vigor occurs. However, the Synthetic must be reconstructed periodically, requiring the breeder to maintain all the original lines used in its development.

5.5.2.1. Advantages of synthetic varieties

• They provide a mechanism for capitalising on phenotypic selection while maintaining vigor.

• They allow growers to reproduce seed for a few generations without sacrificing genetic integrity of the variety.

• In developing countries, synthetic varieties offer the possibility of concentrating desirable genes while maintaining high levels of natural diversity.

• Synthetic varieties are used as a maintenance base for genetic diversity.

6. HYBRID MAIZE DEVELOPMENT

Nick Lyimo

One of the modem crop breeding methods that have highlighted the art of crop improvement in the 20th century is the development of the inbred-hybrid concept of maize into a useful fonn. The development and growing of hybrid maize has been a highly successful endeavor and is considered one of plant breeding's greatest achievements ofthe 20th century.

The development of hybrid maize varieties involves three important phases:

• Development of inbred lines by controlled self pollination. • Line evaluation, in order to determine which inbred lines may be combined into

productive crosses. • Commercial utilization of the crosses for seed production.

6.1. Development of inbred lines

An inbred line is a pure line developed by repeated self pollination and selection until apparently homozygous plants are obtained. This procedure usually requires at least seven


generations of inbreeding. The purpose of inbreeding is to fix desirable characters in a homozygous condition in order that the lines so developed may be maintained without genetic change.

There are two key factors that must be very carefully considered in order for the breeder to succeed in the development of useful maize inbred lines.

6.1.1. Source of Germ plasm.

lt is important that lines be developed from appropriate sources, in order to maximize the chances of generating lines that have potential as parents for useful hybrid combinations. Germplasm sources of the original groups of lines used for hybrid varieties (in the USA in the 1920's and 1930's) consisted mainly of popularly known open-pollinated cultivars. It was soon realized, however, that the frequency of superior lines could not be significantly increased, even after the original source populations were re-sampled. None of the selected lines met all the requirements for stability of yield, standability, pest resistance and combining ability. The selected lines were elite relative to other lines, but each line usually had traits that could be improved. Therefore, other more suitable sources of lines had to be sought.

The next logical breeding procedure was, therefore, to cross elite lines that complemented each other for the different traits and to select lines within the F2 populations that possessed the desirable traits of the two parents. Thus, selection within F2 populations of elite line crosses has largely been adopted as an important source of germplasm for inbred line development. This source of gem1plasm has and continues to be exploited using the pedigree method of line development, a procedure which is very popular and widely used in the development of maize inbred lines.

Briefly, in the pedigree approach, individual plants are selected in the segregating generations (from crosses such as those described above) on the basis of their desirability, judged individually and on the basis of records maintained of all parent-progeny relationships. An illustration of the pedigree method of line development is presented in section 6.5 of this chapter.

6.1.2. The inbreeding phase.

Shull (1909, 191 0) suggested self pollination as a method for inbred line development. Today, self pollination is still the standard method used by maize breeders to attain the same objective. Self pollination is the most rapid fom1 of inbreeding available for the attainment of homozygosity. As shown in Table 6.1, below, heterozygosity is reduced by 50% just after one generation of inbreeding, and by the 4th. generation, almost 94% homozygosity will have been attained. Note that percent increase in homozygosity is equivalent to the percent decrease in heterozygosity as inbreeding progresses from one generation to the next.

Table 6.1. Reduction in heterozygosity over 4 generations of self fertilization in maize

Generation 0

Percent heterozygosity 100 50 ,.,-~)

12.5 6.25

Percent homozygosity 0 50 75 87.5 93.75

Regional Maize Course for Technicians, Arusha, Tanzania June \997 - Page 45

Along with increase in homozygosity, inbreeding in maize causes a reduction in vigor and productivity, as well as a delay in flowering. Estimates of inbreeding depression have been studied and reported by Hallauer and Miranda (1988). They f(mnd that maize on the average will be 68% lower yielding at the inbred level compared with the non-inbred, and that plant height will be reduced by 25% and days to flowering will increase by 6.8% with inbreeding to homozygosity. The effects of inbreeding, however, depend on source populations and the past selection records of populations that are sampled. Rodriguez and Hallauer (1988) reported that the effects of inbreeding in populations undergoing recurrent selection were less than in the Lmselected populations. S1 progenies of populations under half-sib and full-sib reciprocal recurrent selection had 6.6% less inbreeding depression for grain yield than the original unselected populations. S 1 progenies from half sib recurrent selection in one population had 17.4% less inbreeding depression than the unselected populations. What is the explanation for this? It appears that inbreeding depression occurs because of the effects of deleterious recessive alleles. Germplasm enhancement, therefore, seems to be an effective method of increasing the frequency of favorable alleles, which in turn, decreases the effects of inbreeding depression.

6.2. Methods of inbred line evaluation

ln maize breeding, inbred line development is a relatively easy task to accomplish. However, the objective of the breeder is not to find the best pure line, but rather, to find and maintain those lines that make the best hybrid combinations. The evaluation of lines in all possible crosses in order to identify the best hybrid combinations is, therefore, the most important and difficult aspect of hybrid maize development. How can lines that give the best hybrid combinations be identified?

In order to appreciate the importance and complexity of this phase of hybrid development, it is appropriate to take note of two key facts as described below.

6.2.1. Line development

The number of inbred lines rapidly builds up to almost unmanageable levels. With a relatively small number of lines, all possible crosses among Iines can conveniently be made, followed by evaluation of cross performance in order to identify the best hybrid combinations. In a given set of inbred lines, "N", the number of all possible crosses is given as N(N-1)/2. When N is large, it becomes impossible to mal(e all possible combinations for evaluation. For example, evaluation of 1000 lines in all possible single cross combinations would involve [1000(999)]/2 = 499,500 hybrids, an impractical nwnber of entries to test in any breeding program.

6.2.2. Evaluation of inbred lines themselves(~)

Evaluation of inbred lines per se has been shown to have little value because of the inconsistency of correlation between characters of inbreds and their perfonnance in F 1 crosses. Thus, faced with the above two problems, an effective and convenient method of line evaluation had to be devised. The breeder wants to identify a limited nwnber of lines with sufficient genetic potential before their evaluation in specific hybrid combinations is attempted. Davis (1927) and Jenkins and Brunson (1932) suggested the use of a common tester to evaluate inbred lines for general combining ability. This common tester approach is what is now referred to as the Test-cross or Top-cross test, whereby lines at a specified stage of inbreeding are crossed to a common parent referred to as the tester, and the hybrids formed in this mmmer referred to as test crosses or top crosses. Since the tester is the same for all lines under evaluation, differences in performm1ce m11ong top crosses will re£1ect differences in the


general combining ability of the lines. General combining ability refers to the average perfonnance of a line in crosses with other parents. Specific combining ability is the perfom1ance of a line in a cross with a specific parent. For example, if line AI is crossed to parents P 1 , P2, and P3, the average perfonnance of A 1 x P 1, A 1 x P2, A I x P3 would reflect the general combining ability of line A 1. The specific performance of any of the three hybrids reflects the specific combining ability of line AI with one of the other parents.

What types of testers should be used in this type of evaluation '? The most critical issue in the use of a common tester for evaluation of inbred lines is the choice of an appropriate tester. It is important that the chosen tester be able to classify correctly the relative merit of the lines under evaluation so that the best lines are identified. The testers used to determine general combining ability in the early years of hybrid development were heterogeneous cultivars, populations, or crosses, referred to as broad-base testers. Such testers only gave a measure of the average ability of a line to combine with other lines. The testers most commonly used today for the first evaluation of combining ability of a line are inbred lines with which it would most likely be crossed to produce a commercial hybrid. When the heterotic pattem of the sources of lines is known, choice of testers may be further simplified. For example, if a strong heterotic response is known to exist between two unrelated sources of inbreds (e.g. A and B) then A lines would be evaluated using an inbred tester from B and vice versa. In some instances, when the objective is the replacement of a line in a specific hybrid combination, specific combining ability is of prime importance, and the most appropriate tester would then be the opposite inbred line parent of a single cross or the opposite single cross parent of the double cross. On the basis of results obtained from inbred line evaluations as described above, those lines exhibiting good perfonnance are then advanced to tests involving more testers and eventually to evaluation in specific hybrid combinations. With each year of evaluation, the number of lines decreases and the extensiveness of testing increases tor the lines retained.

6.3. Prediction of hybrid performance

In the preceding section we have seen how the relative worth of large numbers of lines may be evaluated using the test-cross approach. We saw how just a small number of lines may give rise to a large number of single-cross combinations. The evaluation of a group of inbred lines for the production of three-way or double-cross hybrids is also hampered by the large number of cross combinations that are possible.

The formulas tor determining the number of possible crosses among a group of N inbred parents (excluding reciprocals) are given as follows.

• Number of single crosses: n(n-1)/2 • Number ofthree-way crosses: n(n-l)(n-2)/2 • Number of double crosses: n(n-l)(n-2)(n-3)/8

Thus with only 20 inbred lines, there would be 190 possible single crosses, 3420 three-way crosses, and 14,535 double crosses. It is clear that the number of possible three way and double crosses is too large for evaluation. Is there a better way of identifying superior threeway and double cross hybrids '? Jenkins (1934) developed a method of predicting doublecross hybrid performance that has been widely used to identify those combinations of inbred lines that are wm1h further evaluation in field trials. In this procedure, non-parental single cross grain yield data are used to predict both three-way and double-cross hybrid performance.

The performance of a double cross hybrid (Ax B) X (C x D) may be predicted as follows:

(A X B) X (C X D)= 0.25f(A X C)+ (A X D) X (B X C)+ (B X D)]


Note that the parental single crosses, (Ax B) and (C x D) are not included in the formula.

The principle of averaging non-parental single crosses to predict double cross performance can be extended to the prediction of a three-way cross (PI x P2) X P3 as follows:

(Pl x P2) X P3 = 0.5[(P1 x P3) + (P2 x P3)]. Again, note that the parental single cross (Pl x P2) is not considered in the prediction.

As an illustration, assume that four inbred lines A, B, C, and D were evaluated in all possible single-cross combinations and the following yields were obtained in tons per hectare.

A X B = 8.8 A X c = 8.9 A X D = 8.4

B x C = 9.2 B x D = 8.0 C x D = 8.1. The predicted performance of the double cross (Ax C)

x (B x D) would be:

0.25[(A X B)+ (A X D)+ (B X C) +(C X D)]=

0.25[8.8 + 8.4 + 9.2 + 8.1] = 8.6

The predicted performance of the three way cross (Ax D) x C would be 0.5[(A x C)+ (D x C)]

= 0.5[8.9 + 8.1] = 8.5

The use of predicted performance of both three-way and double-cross hybrids is a method by which the breeder is able to determine those hybrid combinations that are worthy of further testing in field trials, in order to reduce the number of combinations that must be evaluated before the most desirable hybrid combinations are identified.

6.3. Commercial utilization of crosses for seed production

Commercial utilization of crosses identified as being superior following test cross performance results (and field trial verification of predicted performance as described above) is the last step in the hybrid maize variety development procedure. At this stage, different types of hybrids may be produced depending on performance, demand, convenience in seed production or any other factors that may favor the production of certain types of hybrids. Hybrids in the broadest sense, are the progeny of the mating of two non-identical parents. As a matter of commercial practice, there are several categories of hybrids, as briefly described below.

6.3.1. Single-cross hybrid

A single-cross hybrid involves a cross between two unrelated inbred lines (A x B). Single crosses provide the greatest opportunity for expression of heterosis (hybrid vigor) and usually have higher yield potential than other types of hybrids. They also provide maximum unifonnity for various plant characteristics, including important traits such as maturity and ear placement. The main disadvantage of single-cross hybrids is that in most cases the inbred line used as the female parent usually produces lower seed yield than the kinds of parents used to produce other types of hybrids. However, through improved agronomic practices and development by maize breeders of inbred lines with higher ~ se yields, the production of seed of certain single-cross hybrids appears to be economically feasible.

6.3.2. Modified single-cross hybrid

This is the cross of an Fl hybrid produced by crossing two related inbred lines (Ax A') with an unrelated inbred line C. i.e. (A x A') x C. In order to overcome the problem of a low


yielding female line as described for single-cross hybrids above, use of a cross between two related lines as the female parent in this type of hybrids ensures more seed production while most of the uniformity characteristics expressed in single-cross hybrids are maintained.

6.3.3. Double modified single-cross hybrid

* The mating used to produce a double modified single cross hybrid takes the form (A x A) X * * * . (B x B). Thus A and A are closely related lines so are B and B. The cross servmg as a

female should produce more seed than either parent used alone. Similarly the cross serving as the male should produce more pollen than either parent used alone.

6.3.4. Three-way cross hybrid

A three-way cross hybrid (Ax B) x C, is produced by crossing two unrelated inbred lines (Ax B) and using the single cross as a female parent for hybridization with an unrelated inbred line (C) as the male parent. With this type of hybrid, seed production costs may significantly be minimized since the female parent is a single cross hybrid which is expected to produce large quantities of seed.

6.3.5. Modified three-way cross hybrid

Sometimes it may be desirable to produce a modified form of a three way cross, (Ax B) x (C' x C), where the male parent happens to be a cross between two related inbred lines. This type of hybrid combination may be used when it is desirable to enhance the male parent for pollen producing ability or general vigor.

6.3.6. Double-cross Hybrid

This type of hybrid may also be referred to as a four-way cross. It involves the cross of two different Fl hybrids, [(Ax B) x (C x D)] each having no inbred parent in common with the other. The first hybrids produced and sold commercially were almost exclusively double crosses before transition to other forms of hybrids took place. While this type of hybrid combination is still in use in many cow1tries, it is virtually non existent in other areas, e.g., in the USA and Canada, where single crosses now comprise at least 90% of the hybrid seed sold in these countries.

6.4. Advantages and disadvantages of maize hybrids

Comparisons among the various types of hybrids may be made by examining their rankings with respect to productivity and uniformity in a commercial field, the cost of hybrid seed production and the number of different plantings required for hybrid seed production.

6.4.1. Productivity

The rank of the hybrid types from the most to the least productive in a commercial field is single cross, modified single cross, double modified single cross, Three-way cross, modified three-way cross and the double cross. The greater productivity of the single cross makes it the preferred hybrid type in many countries, especially the Unites States, where it is now the most predominant hybrid type.

6.4.2. Unifonnity

The uniformity of plants in a commercial field may be an advantage in obtaining uniform seeds for marketing and in facilitating harvesting. The rank order of hybrids from the most to the least unifom1 is single cross, modified single cross, double modified single cross, threeway cross, modified three-way cross and the double cross. A single cross hybrid produced


from two inbred parents is the most uniform because all of the plants are genetically alike. A double-cross hybrid involves genetic segregation of the alleles from four parents and is, on the average, the least uniform of the hybrid types.

6.4.3. Cost of hybrid seed production

The cost of large scale production of hybrid seed is related to the relative quantity and quality of seed obtained from different types of female parents and the quantity of pollen provided by different types of male parents. Inbred parents have the smallest production of seed and pollen, crosses between related parents are more productive, and single-cross parents are the most productive. Therefore, the single-cross hybrid is the most expensive to produce because both parents are inbreds, while the double cross hybrid is the least expensive because both parents are single crosses. The rank of hybrid types from the most to the least expensive to produce is single cross, modified single cross, double modified single cross, three-way cross, modified three-way cross and the double cross.

6.4.4. Number of plantings

The production of seed of each parent and of the hybrid itself requires separate plantings that are properly isolated to maintain genetic purity. Table 6.2 indicates the number of separate plantings required to produce different hybrid types and their parents.

Table 6.2. Number of separate plantings required to produce different types of hybrids and their parents

Hybrid Type Single Cross Modified Single cross Three-way cross Double Modified Single Cross Modified Three-way Cross Double Cross

No. of Separate Plantings 3 5 5 7 7 7


6.5 Pedigree method of hybrid development

An illustration of the pedigree method (with some modification to reflect line development in maize) is outlined below. Basically, there is no difference in its implementation for self or cross-pollinated species, except that inbreeding by self pollination occurs naturally in inbreeders, while for cross-pollinated crops it must be done manually. Selection generally begins with an F2 or SO population and continues until homogeneous lines are developed.

Season

1

2

3

4

5

6

7

Procedure

Grow several thousand plants of an

F2 population. Select and selfbest 500 individual plants. Harvest best S 1 ears

Grow S 1 ears (ear-to-row) Select best rows. Self best S 1 plants in best rows. Harvest best S2 ears

Grow S2 sears (ear-to-row) Select best rows Self best S2 plants in best rows. Harvest best S3 ears Grow S3 ears (ear-to-row) Select best rows Self best S3 plants in best rows Top cross several plants in best rows to a common tester. Harvest best S4 ears. Harvest top cross seed for combining ability evaluation

Grow S4 ears (ear-to-row) Self best S4 plants in all rows Harvest best SS ears based on combining ability evaluation

Grow S5 ears (ear-to-row) Selfbest S5 plants in all rows Select best S6 ears in each row and bulk individual lines

Grow S6 lines (each from bulk seed) Continue with selfing ofbest lines identified on the basis of combining

Evaluate top-cross progenies at 2 to 3 locations. Identify best lines based on top-cross performance data

While inbreeding to homozygisity is in progress, three-way and double-cross hybrid combinations may be in order to initiate hybrid production using S5 or S6 lines, and later using fully homozygous lines.


ability tests until fully homozygous lines are obtained

Again note that line development by the pedigree method can take many different approaches and many modifications. The example above is just one among the many ways that the procedure may be executed. The most important thing is to keep elaborate records that reflect the genetic relationship among the lines that are developed.

6.5 .1. Merits and demerits of the pedigree method

6. 5 .1.1. Advantages

• If selection is effective, inferior genotypes may be discarded before inbred lines are evaluated in expensive replicated tests.

• Selection in each generation involves a different environment, which provides a good opportunity for genetic variability of important characters to be expressed and effective selection to be practiced.

• The genetic relationship of lines is known and can be used to maximize genetic variability among lines retained during selection.

6.5 .1.2. Disadvantages

• The pedigree method cannot be used in environments where genetic variability for characters is not expressed. This may prevent the use of off-season facilities, with an associated increase in the length of time for cultivar development compared with other methods of inbreeding.

• A considerable amount of record keeping is involved. • Experienced persons may be required to make necessary selections. • The method requires more land and labor than other methods of inbreeding.

6.6. Hybrid vs. open-pollinated varieties

6.6.1. Assisting the farmer in making the right choice

The comparison between hybrids and open-pollinated varieties (OPV's) is an issue which should be carefully evaluated with the objective of assisting the fanner in choosing the best adapted variety. Although higher yields may be a primary goal, it is important to realize that farmers also have other priorities other than yield alone. Therefore, apart from yield, the other varietal characteristics farmers need (e.g. maturity and grain type) must be carefully considered when assisting them in choosing between hybrids or open pollinated varieties. The type of farmers and the farming conditions under which the varieties are to be grown will also very much influence the choice of variety to be grown. It should be borne in mind that a hybrid maize variety will not always show superiority over an OPV. In certain environments some OPV's have performed better than hybrids, and under such circumstances, OPV's rather than hybrids should be recommended for production.

Below is a brief look at the merits and demerits of both hybrids and open-pollinated varieties. As already stated above, a mere consideration of the advantages and disadvantages of hybrids and OPV's is not enough in arriving at the correct decision as to which varieties a farmer must grow. Other factors must also be considered alongside the advantages and disadvantages of these materials.

6.6.2. Advantages of open-pollinated varieties

6.6.2.1. Lower seed cost


Seed production costs are relatively low, and seed quantities of open pollinated varieties can be built up quite rapidly. Commercial grain production is only two generations away from the breeders seed. As a result of lower seed production costs, the cost of seed to the farmer is, therefore, much lower than it is for hybrid seed. Cost of seed to the farmer is lowered further by the fact that he does not have to purchase fresh seed every season. With good husbandry, the farmer may select and bulk seed from his production plot for up to 3 seasons before purchasing a fresh supply of seed.

6.6.2.2. Simple maintenance and seed production procedures

With open pollinated varieties, planned seed production targets can be easily and rapidly achieved. Research can more quickly develop new varieties in response to maize production problems. New and better varieties extracted from on-going population improvement activities can quickly replace old ones when desired, for example, in the event that an existing open pollinated variety becomes susceptible to a certain disease.

6.6.2.3. Recycling of seed by farmers

In areas where an efficient seed distribution system is lacking, open pollinated varieties have a clear advantage because such varieties can move from farmer to farmer and be saved by the farmer for several years. The distribution system is so important that it can directly affect the goals of a crop breeding program. For example, distribution difficulties have caused some maize breeding programs to change from developing hybrids to concentrating on open pollinated varieties.

6.6.2.4. Germplasm exchange

Exchange of germ plasm among national programs is easier with open pollinated varieties than it is with some closed pedigree maize materials that involve proprietary rights.

6.6.3. Advantages ofhybrids over OPV's

6.6.3.1. Yield potential

In most instances, hybrids have higher yields under the conditions for which they are recommended as compared to OPV's.

6.6.3.2. Uniformity for various characters

Hybrids are distinctly more uniform than OPV's for cob size, cob placement, grain size, grain type, as well as maturity. Uniformity with regard to cob placement and maturity creates convenience for machine harvesting, while uniformity for grain type and size may facilitate marketing of maize in the event of abundant grain supply.

6.6.3.3. Potential for research to boost yield

There is greater potential for research to continue increasing grain yield through development of better inbred line parents for new hybrids, as well as through inbred line replacement or modification for existing hybrids.

6.6.4. Disadvantages ofhybrids

There are, however, several factors which stand out as disadvantages especially in relation to the small-scale fanner, when it comes to use of hybrid seed. Although small-scale farmers may appreciate the potential of hybrid seed, they may fail to have access to these materials, owing to the relatively higher seed costs and the fact that fresh seed must be purchased every season. Furthermore, use of hybrid seed goes along with a higher demand for other expensive

Regional Maize Course tor Technicians, Arusha, Tanzania June 1997 - Page 53

inputs such as fertilisers and pesticides in order to ensure exploitation of the potential of hybrid seed for profitable maize production. This is an additional constraint to the small-scale farmer. In the event of production problems faced by the farmer, it is more difficult for research to respond with the necessary changes or modifications because of the amount of time required to test new hybrid combinations, as well as the long time it takes for a new hybrid variety to reach the farmer after it has been officially released.

6. 7. References

Davis, R. L. 1927. Report ofthe plant breeder, p. 14-15.ln: Puerto Rico Agric Exp. Stn. Annu. Rep.

Hallauer, A. R .. and J. B. Miranda Fo. 1988. Quantitative genetics in maize breeding. 2nd. ed. Iowa State Univ. Press. Ames, IA.

Jenkins, M. T., and A.M. Brunson. 1932. Methods oftesting inbred lines ofmaize in crossbred combinations. J. Am. Soc. Agron. 24:523-530 .

.Jenkins, M. T. 1934. Methods of estimating the performance of double crosses of com. I. Am. Soc. Agron. 26:199-204.

Rodriguez, 0. A.. and A. R. Hallauer. 1988. Effects of recurrent selection in corn populations. Crop Sci. 28:796-800.

Shull, G. H. 1909. A pure line method of com breeding. Am. Breeders Assoc. Rep. 5:51-59. Shull, G. H. 1910. Hybridization methods in corn breeding. Am. Breeders Mag. 1 :98-1 07.

7. FERTILISERS: DEFINITIONS AND CALCULATIONS

John Kumwenda

7.1. Soil fertility and nutrient availability

Soil fertility is the ability of the soil to supply nutrients essential for plant growth (Kang, 1995). Soil fertility focuses on adequate and balanced supply of nutrients to satisfy the needs of plants, avoiding toxic concentrations (Kang, 1995). Fertilisers whether organic or inorganic, natural or synthetic, provide plants with nutrients. There are 16 elements known to be essential for plant growth. These are listed in Table 7 .1. They are divided into two main groups, non-mineral and mineral. Non-Mineral Nutrients are carbon (C), hydrogen (H) and oxygen (0). These nutrients are found in the atmosphere and water. They are used in photosynthesis as follows:

6C02 +

Carbon Water ----• Oxygen

+ 6(CH20)

Carbohydrates + Carbon Dioxide

The 13 Mineral Nutrients - those coming from the soil - are divided into three groups: primary, secondary and micronutrient (see Table 1 below):


Table 7.1. Essential nutrients

MacronutrientsA vail able from air and water

Micronutrients

Primary elements

Secondary elements

carbon hydrogen oxygen

nitrogen phosphorus potassium

calcium magnesium sulphur

boron chlorine copper Iron manganese molybdenum zinc

In Table 7.1, the first 9 elements (C, H, 0, N, P, K, Ca. Mg, and S) are required in relatively large amounts and are called MACRONUTRIENTS. Elements likeN, P, and K are known as Primary Nutrients, while Ca, Mg, and S arc known as Secondary Nutrients. The remaining nutrients (B, Cl, Cu, Fe, Mn, Mo, and Zn) are required in relatively small amounts and are called Micronutrients.

In addition to the I 6 essential elements listed above, some other elements are helpful in improving yield and quality of crops. Examples are sodium, silicon, cobalt and selenium. Most commercial fertilisers contain at least one of the primary elements in a form available to plants in specified amounts.

7.2. Nutrient gains and losses in soils

Nutrient gains in the soil are through, nutrient release by:

• Mineralisation and weathering, • The application of mineral and organic fertili:>ers, • Nitrogen fixation by legumes • Supply of nutrients contained in rain or snow.

Nutrient losses are mainly through:

• Crop removal • Leaching especially N (Little or no loss of P due to leaching) • Volatilisation/denitrification (NH3, N2> N20). • Erosion

7.3. Nutrient use efficiency (NUE) by crops

Nutrient use efficiency can be improved in crops by minimising losses through leaching, runoff, volatilisation/denitrification. This can be achieved by:

• Using recommended fertiliser rates. • Use of improved varieties of crops which have the ability to take up more nutrients.


• Split application of fertilisers. • Proper timing of fertiliser application. • Use of slow-release fertilisers. • Timely weeding.

7.4. Defrnitions and terminology (Source Kang, 1995).

7.4 .1. Fertiliser: A fertiliser is a manufactured product containing a substantial amount of one or more of the primary, secondary macronutrients or micronutrients. TI1e terms "chemical fertiliser" are used to distinguish the manufactured products from natural organic fertilisers of plant or animal origin which are called "organic fertilisers".

7.4.2. Grade: The grade of a fertiliser is the nutrient content in weight percentage ofN, P20 5

and K20 in the order ofN-P-K. The grade is only the amount of nutrient found by prescribed analytic procedures, excluding any nutriel)t that is available to plants. For example, a grade of "1 0-15-18" indicates that in a 100 kg of the fertiliser 10% or 10 kg is N, 15% or 15 kg is P20 5,

and 18% or 18 kg is K20, and the balance (57% or 57 kg) is the carrier.

7.4.3. Straight fertiliser: Fertiliser containing only one nutrient, for example urea or superphosphate, muriate of potash, or ammonium nitrate.

7.4.4. Compound fertiliser: Fertiliser containing two or more nutrients such NPK fertilisers, e.g. 23:21:0+4S, 20:20:0, 15-15-15.

7.4.5. Granular fertiliser: Fertiliser in the form of particles such as 20-20-0.

7 .4.6. Prilled fertiliser: A granular fertiliser with round grains, e.g. prilled urea.

7.4.7. Coated fertiliser: Granular fertiliser coated with a thin layer of substances, such as clay or sulphur, to prevent caking or to control dissolution rate, e.g. Sulphur-coated urea.

7.4.8. Nongranular or powdered fertiliser: Fertiliser containing fine particles usually with some upper limit size, such as 3 mm but lower limit, e.g. elemental sulfur.

7.4.9. Conditional fertiliser: Fertiliser treated with an additive to improve physical condition or prevent caking. The conditioning agent may be applied as a coating or incorporated in the product.

7.4.1 0. Bulk fertiliser: Unpacked fertiliser.

7.4.11. Bulk-blend fertiliser or blended fertiliser: Two or more granular fertilisers of similar size mixed together to form a compound fertiliser.

7 .4.12. Liquid or fluid fertiliser: A general term of liquid fertilisers including fertilisers that are readily or partially soluble, clear liquids and liquids containing solids in suspension.

7.4.13. Solution fertiliser: Liquid fertiliser dissolved in water and free solids. Some common fertiliser carriers of mineral nutrients are listed in Tables 7.2-7.12.


Table 7.2. Some common nitrogen fertiliser sources with their N content.

Source

Ammonical/nitrate sources

Anhydrous Ammonia

Aqua Ammonia/N solutions

Ammonium nitrate

Ammonium Nitrate Sulphate

Ammoniwn Sulphate

Ammonium Nitrate/Lime

Mono-ammonium phosphate (MAP)

Di-ammonium phosphate (DAP)

Ammonium Chloride

Urea

Nitrate sources

Sodium nitrate

Potassiwn Nitrate

Calcimn Nitrate

Slow Available Compounds

Sulphur-coated Urea

Urea-formaldehyde

Magnesium Ammonium Phosphate

PercentN

82

21-49

33.5-34.0

26

21

20.5

11

18-21

26

46

16

13

15.5

39

38

9

Note that mineral fertilisers contain N in the form of nitrate (N03-), ammonium (NH/) or urea. Ammonium is partially adsorbed to soil colloids and its uptake rate is usually therefore lower than nitrate under field conditions. Consequently, crops do not respond as quickly to ammonium fertilisers as to nitrate fertiliser application. Nitrate fertilisers are known to produce a rapid response to N in the plant.


Table 7.3. Some common phosphorous fertiliser sources with their P content.

Material

Ordinary superphosphate

Triple superphosphate

Nitrophosphate

Mono-ammonium phosphate

Di-ammonium phosphate

Ammonium polyphosphate

Mono-ammonium polyphosphate

Note that most P containing fertilisers contain Pin the form of phosphate.

Table 7.4. Some common potassium fertiliser sources with K content.

Material

Muriate potash

Sulphate potash

Potassium Magnesium sulphate

Potassium nitrate

of

of

Potassium polyphosphate

Potassium carbonate

Potassium bicarbonate

Nitrogen ('1u)

13

Phosphorus (%)

25-50

Potassium (%)

50-52

44

18

37

20-40

56

39

16-22

46

20-24

48

46

34

11-52-0

Sulphur (%)

18

22

Magnesium (%)

II


Table 7.5. Some common calcium fertiliser sources with Ca content.

Material

Calcitic limestone

Dolomitic limestone

Basic slag

Gypsum

Marl

Hydrated lime

Burned lime

Percent Ca

31.7

21.5

29.3

22.5

24.0

46.1

60.3

Based on pure calcium carbonate at 100%

Relative Neutralising Value*

85-100

95-108

50-70

None

15-85

120-135

150-175

Table 7.6. Some common magnesium fertiliser sources with Mg content.

Material

Dolomitic limestone

Magnesia(Mg Oxide)

Basic slag

Magnesium sulphate

Potassium-Magnesium sulphate

PercentMg

11.4

55.0

3.4

17.0

11.0


Table 7.7. Some common sulphur fertiliser sources with S content.

Material

Elemental S

Alwninium sulphate

Ammoniwn sulphate

Basic slag

Copper sulphate

Iron sulphate

Gypswn

Magnesium sulphate

Manganese sulphate

Potassium sulphate

Potassium-magnesium sulphate

N om1al superphosphate

Concentrated superphosphate

Ammonium sulphate

Ammonium sulphate nitrate

Ammoniwn thiosulphate (solution)

Sodium sulphate

Sulphur dioxide

Urea-gypsum

Zinc sulphate

PercentS

30-100

14.0

23.7

3.0

12.8

19.0

12.0

13.0

14.5

18.0

22.0

11.9

1.4

24.2

12.1

26

22.6

50

14.8

17.8


Table 7.8. Some fertiliser sources of boron with B content.

Source Percent B Water Soluble

Borax 11.3 Yes

Sodium pentaboratc 18.0 Yes

Sodium tetraborate

Fertiliser borate 46 14.0 Yes

Fertiliser borate 65 20.0 Yes

Boric acid 17.0 Yes

Colemanite 10.0 Yes

Solubor 20.0 Yes

Boron frits 2.0-6.0 No

Table 7.9. Some common copper fertiliser sources with Cu content.

Source Percent Cu Water Soluble Application Methods

Copper sulphate 22.5 Yes Foliar, soil

Copper ammo mum 30.0 Slight Foliar, soil

phosphate

Copper fhts Variable No Soil

Copper chelate Variable Yes Foliar, soil

Other organics Variable Yes Foliar, soil


Table 7.10. Some common iron fertiliser sources with Fe content.

Source Fe Percent

Iron sulphates 19-23

Iron oxides 69-73

Iron ammonium sulphate 14

Iron f!·its* Variable

Iron ammonium polyphosphate 22

Iron chelate 5-14

Other organics 5-10

*Not suitable as a foliar spray or for use on alkaline or calcareous soils.

Table 7.11. Some manganese fertiliser sources.

Source Mn Percent

Manganese sulphates 26-28

Manganese oxides 41-68

Manganese chelate 12

Manganese carbonate 31

Manganese chloride 17

Manganese frits 10-25

Table 7.12. Some common zinc fertilisers and their Zn content.

Source Zn Percent

Zinc sulphates (hydrated) 23-35

Zinc oxide 78

Basic zinc sulphate 55

Zinc carbonate 52

Zinc sulphide 67

Zinc frits Variable

Zinc phosphate 51

Zinc chelate 9-14

Other organics 5-10


Table 7.13. Conversion factors from oxide to elemental basis. For example, the grade 10-15-18 (N-P20 5 + K20) becomes 10-6.5-14.9 (N-P-K).

The grade may also be called 'analysis' or 'fonnula'.

P20:; X 0.44 p p X 2.29 P20s K20 X 0.83 K K X l.20 K20 CaO X 0.71 Ca Ca X 1.40 CaO MgO X 0.60 Mg Mg X 1.66 MgO S02 X 0.50 s s X 2.00 S02

Source:Kang (1995)

7.5 Fertiliser Calculations

Fetiiliser recommendations are expressed in kilograms of nutrients per hectare (kg/ha) in the order N- P20 5 - K20 (or N-P-K). If only nitrogen is needed, for example, the rate is given in kilograms of nitrogen (N) per hectare (e.g. 40 kg N/ha).

Fertiliser rates are fommlated based on results of field trials or results of soil analysis.

7.5.1. Calculation for a single-element fertiliser:

Required information:

• Know the recommended application rate (R) (kg/ha). • Know the concentration or active ingredient (C) of the fertiliser(%). • Know the area to be fertilised (ha or m\

Question. Calculate amount of fertiliser required per hectare (ha) by dividing application rate (R) by analysis (C).

Equation 1:

Fertiliser required (kg/ha) = R (kg/ha) x 100 C(%)

Example 1. Calculate the amount of fertiliser urea per hectare if 92 kg/ha N is to be applied per hectare. Urea contains 46% N.

Urea kg/ha = 92 kg/ha x 100 = 200 kg/ha of urea 46%

Example 2. Calculate the amount of fertiliser triple superphosphate (TSP) (46% P205) per hectare if23 kg/ha P20 5 is to be applied per hectare.

TSP kg/ha = 23 kg/ha x 100 =50 kg/ha ofTSP 46%

Example 3. Calculate the amount of fertiliser potassium chloride or muriate of potash (60% K20) per hectare if 30 kg/ha K20 is to be applied per hectare.

Muriate of potash kgllm = 30 kg/ha x 100 =50 kg/ha of muriate ofpotash 60%


7.5.2. Calculation of fertiliser per certain area.

Things to know.

• Know the amount or rate of fertiliser nutrient to be applied per ha. • Know the area to be applied. • Know the active ingredient in the fertiliser.

Example. Suppose you would like to apply 92 kg/haN. How much urea (46% N) would you apply in a plot which is 350m2?

Note: a). Calculate the amount of fertiliser required per m2 by dividing the required amount per ha by 10,000 (1 ha = 10,000 m\

b). Calculate the amount of fertiliser required for the area to be fertilised. Multiply the required amolmt per m2 by the number ofm2 of the area to be fertilised.

Example 4.

Fertiliser required (kg/ha) per 350m2 = 2 R (kg/ha) x 100 x 350m-

C(%) x 10000 m 2

Urea kg/350m2 2 =92 kg/ha x 100 x 350m- = 7 kg ofurea 46% x 10000 m2

The above calculation can also be used to obtain the amount of fertiliser per planting station of maize by knowing the area of a planting station e.g. 0.90 m x 0.90 m = 0.81 m

2 or 0.90 m x

0.30 m = 0.27 m2. The calculation can also be used to obtain the amount of fertiliser to be

applied per given m row length when using the broadcasting or banding method of fertiliser placement The area can be obtained by multiplying the row length x the width of the row,

2 e.g. 10mx0.90m=9m.

7.5.3. Calculation of fertiliser per maize plant. plant,

To apply a quantity of fertiliser per know the following:

• Know amount or rate of fertiliser nutrient to be applied per ha. • Know population density of the maize crop per hectare. • Know the active ingredient in the fertiliser.

Example 5. Suppose we would like to apply 92 kglha N. How much urea (46% N) should we apply per maize plant if maize is planted at a population density of 44,000 plants per ha?

Fertiliser required per plant= R (kg/ha) x 100 x 1 (plant) C(%) x 44000 plants/ha

Urea kg/plant = 92 kg/ha x 100 x 1 plant = 0.0045 kg/plant of urea or 46% x 44000 plants/ha 4.5 g/plant

7.5.4. Calculation for combinations of single-element fertilisers

For exan1ple, a recommended rate of 92 N - 46 P20 5 - 30 K20 kg/ha can be achieved by combining single-nutrient fertilisers, such as urea, triple superphosphate, and muriate of potash.

Calculate first the amount ofurea (46% N) required, then the amount of triple superphosphate (46% P20 5) and muriate of potash (60% K20) to satisfy the recommendation 92-46-30- kg/ha using Example 1 :


Example 6

Urea kg/ha 92 kg!ha x 100 = 200 kg/ha ofurea 46%

Triple superphosphate 46 kg/ha x 100 = 100 kg/ha 46%

Muriate of potash 30 kg/ha x 100 = 50 kg/ha 60%

7.5.5. Calculation for combination of single-nutrient and compound fertilisers

Note: A compound fertiliser may be used as a basal dressing (at planting), while a single fertiliser for top-dressing.

An application rate of 92-30-30 kg/ha can also be achieved by combining single nutrient fertilisers with compound fertilisers.

Example 7:

A 15-15-15 fertiliser and urea (46% N) are recommended for the 92-30-30 kg/ha fertiliser application.

In the recommended rate 92 N - 30 P20 5 - 30 K 20 kg/ha, less amounts of phosphorus and potassium are required. Phosphorus and potassium must be calculated first:

30 kg/ha x 100 = 200 kg/ha Phosphorous or potassium 15%

200 kg of a 15-15-15 compound fertiliser supplies only 30 kg of N per ha. This means that 62 kg ofN must be supplied from urea:

62 kg/ha x 100 = 135 kg/ha urea 46%

Example 8. Suppose a 20-20-0 fertiliser and urea (46% N) are recommended for the application of 120-40 kg/ha N:P20 5 fertiliser. Using example 7, phosphorous should be calculated first:

Phosphorous kg/113 = 40 kg/ha x 100 = 200 kg/ha 20%

200 kg of a 20-20-0 compound fettiliser supplies only 40 kg ofN per ha. This means that 80 kg ofN should be supplied from urea:

80 kg/ha x 100 = 174 kg/ha urea 46%

7.5.6. Calculation of fertiliser requirements for a certain area using a combination of a single and compound fertiliser

Recommended application rate Area to be fertilised Urea Diammonium phosphate (DAP)

120-40-0 350m2

46%N 18-46-0

If diammonium phosphate (DAP) and urea are used, the amount of P20 5 required for 350 m2

(0.0350 113) is:


40 kg/ha x 100 x 0.0350 ha = 3.04 kg DAPper 0.0350 ha 46%

This 3.04 kg ofDAP also provides 18% ofnitrogen corresponding to:

3.04 kg x 0.18 = 0.547 kg or 547 g N per 350m2

or 2 0.547 kg N x 10,000 m- = 15.6 kg N/ha

)

350m-

According to the recommended application rate you still need to add 120-15.6 = 104.4 kg N/ha. Thus you must still provide additional urea:

2 (120-15.6) kg N/ha x 100 x 0.0350 ha = 7.9 kg urea/350m 46%


8. SOIL AND PLANT ANALYSIS: INSTRUCTIONS FOR SOIL AND PLANT SAMPLING

John Kumwenda

8.1. Introduction

Soil and plant analysis is part and parcel of the soil fertility evaluation program. Soil fertility deals with plant nutrient elements and soil conditions, whereas evaluation is concerned with levels and availability of nutrients and nutrient balance in the soil, including appropriate methods for assessing these factors (soil tests, plant analyses, soil surveys and climatic monitoring). Once the levels of availability of nutrients and nutrient balance in the soil and plant have been assessed by analysing soil and plant samples, the soils are improved with the addition of fertilisers, lime, manures and other amendments in such quantities to provide the optimum nutrients for crop production.

8.2. Soil Sampling.

The main objective of conducting soil analysis is to determine the chemical and physical properties ofthe soil, so that corrective measures can be taken if any ofthese factors falls short of the nonnal requirements for economical and profitable crop production.

8.3. Characterisation of an experimental site. (Principles of Soil Sampling).

Before an experiment is implemented, the experimental site should be characterised for its soil chemical and physical properties. Soils should be collected at depths determined by the principal scientist. For example, many scientists sample soil at increments of 15 em soil depths (e.g. 0-15, 15-30, 30-45 em, and so on). For routine soil analysis on cultivated areas, top 0-15 em and 15-30 em soil depths will often suffice. The top soil is especially important because it provides most of the nutrients required for plant uptake.

8.4. Principles of soil sampling.

• Take several (1 0-20) samples throughout the experimental site. Put the samples in a large plastic bucket and mix well to form a composite sample. Send I to 1.5 kg of this composite sample to the soil testing laboratory.

• Do not mix different soil types (different colors or textures) to make the composite sample. If the field has different soil types, separate composite samples should be formed from each soil type. If different areas of a field show differences in plant growth, productive areas should be sampled separately from unproductive areas.

• In fields where fertilisers have been applied in the row, a composite sample should be taken on the rows and another from between the rows.

• Soils should be sampled when dry. If the soil is slightly moist, place it in the sun or at room temperature to dry.

• Place the dried soil in a strong clean bag (paper, cloth, or plastic). Label each sample bag with the date, field name, reference number, and depth of sampling. Place a label with identical infonnation inside the bag with the soil. Close the bag securely. Other information should include: crop sequence and fertilisation history.

8.5. Soil sampling in an experiment during the growing season or after harvest.


Depending on the objectives of the experiment or data to be collected, soil samples may be collected to detennine nutrient flow, uptake or residual effects from fertiliser treatments. The following guidelines should be followed:

• Four to 5 soil samples should be collected, at known depths, in each treatment and composited. When wet soil is collected, dry in the sun or at room temperature on a clean dry paper or news paper.

• When fertilisers have been applied on the ridge either by banding, broadcasting on the Label soil samples properly. For example, title of the experiment, name of the site, date of sampling, depth trom which the sample is collected, treatment number, replicate number, condition of the field at sampling.

8.6. Plant Sampling

Plant analysis is a diagnostic tool and can be applied when one wants to:

• Help identify deficiency symptoms or confinn a suspected nutrient element deficiency, seen by visual symptoms, before supplying a corrective treatment.

• Determine nutrient supplying power of the soil.

• Aid in detem1ining the effect of a fertiliser treatment on the nutrient supply in the plant.

• Monitor plant nutrient status and crop performance.

8.6.1. Time of san1pling and testing.

Depending on the objective of the experiment or study, plant analysis and hence plant sampling can be done any time during the growth cycle of the plant. However, the most critical time of growth for plant analysis is at the flowering or from flowering to early fruiting stage. During this period nutrient utilisation is at its maximum, and low levels of nutrients are more likely to be detected. Again, depending on the objectives of the plant analysis, whole plants or plant pm1s (say leaves) can be smnpled for m1alysis. In maize, ear leaves are sampled at silking. Em· leaves are collected when silks are still wet.

In an experiment, 8-10 plants or plm1t parts (say ear leaves) should be collected at random a11d composited, and dried.

Do not sample when the plant is covered with soil, dust, or damaged by insects, injured mechanically or diseased. Do not include dead plant tissue in a collected sample unless it forms a sample of its own. Also do not sample when plants are under moisture or temperature stress.


8.7. References

Aldrich, S.R., W.O. Scott, and E.R. Leng. 1976. Modem Corn Production (2nd ed.). Libray of Congress Number 75-13504. Arnon, I. 1975. Mineral Nutrition of Maize. International Potash Institute, Bern Switzerland.

A1mon. 1979. Soil Fertility Manual. Potash and Phosphate Institute, USA. CMRT. 1995. Field book and Guidelines for 1995 Training Crop Management Manual. Njoro, Kenya. Kang, B.T. 1995. Fertilisers: definitions and calculations. IITA Research guide 24. ITTA,

lbadan, Nigeria. Mengel, K., and E.A. Kirby. 1987. Principles of Plant Nutrition. (4th ed). International Potash Institute, Bern, Switzerland. Tisdale, A.M., W.L. Nelson, and J.D. Beaton. 1985. Soil Fertility and Fertilisers. (Fourth ed.)

Macmillan Publishing Company, Ney York.

9. WEED CONTROL

John Kumwenda

9.1. Definition of Weeds.

Some definitions of a weed are well listed in the F AO's Weed Hand Book (1986). These include:

• A plant out of place. • A plant not sown whose undesirable features outweigh its desirable features. • A plant or plant part of a plant interfering with the objectives of humans. • Any plant growing where it is not wanted. • A plant whose virtues have not yet been discovered. • An undesirable plant. • A herbaceous plant not valued for use or beauty, growing wild and rank, and regarded as

cambering the ground or hindering the growth of superior vegetation.

9.2. Effects ofweeds on crops.

Weeds compete with crops for nutrients, water, and light. Weeds can also act as hosts of plant diseases and pests, contaminate crop produce and reduce produce quality. The effect of weed competition is greatest when the crop is young, since this is the stage at which crop growth is inhibited most by inadequate amounts of light, water and nutrients (Ross and Lambi, 1985). Thus, crop yields are more likely to be reduced by early season weed competition than late season weed competition.

Most reports that address weed control in maize emphasise the need for timely weed control within the first 5 to 6 weeks after maize emergence (Zimdal1l, 1980), and that thereafter shading by the maize canopy becomes an adequate control device. Most research on weed control in maize has also shown that uncontrolled weed growth can result in significant maize yield reductions of greater than 50%.

Proper weed control can result in efficient use of nutrients and soil water. Kabambe and Kumwenda ( 1995) examined the interaction between weed growth and fertiliser-use efficiency on farmers fields and on Research Stations. They found that weeding twice at the critical periods for the maize crop achieved a higher maize yield, with 45 kg N ha-1 which is half the


recommended fertiliser nitrogen. Weeding late means that more nutrients are required to feed both the crop and the weeds. These results imply that farmers will not achieve optimum yields unless they weed timely. The question is how can we enable farmers to control weeds etiectively and timely? Some of the weed control methods are listed below.

9.3. Methods of Weed Control

Weed control can be done through several practices which include the following:

9.3 .I. Prevention - preventing the entrance of new seeds or plant propagules into an area or preventing seed set on existing plants, e.g. use of clean seed.

9.3.2. Eradication - eliminating all plants and plant parts of a single species from an area. This is very difficult on a large scale and probably uneconomical in most cases.

9.4. Physical control methods

-- Machine tillage or animal draught. --Mowing. -- Hand pulling or hoeing/cutting. -- Flooding, common in rice fields. -- Mulching: use of crop residues, cover crops or a living mulch.

9.5. Cultural control methods

This includes many husbandry or management practices that enhance a crop's ability to compete with weeds. Cultural control is basically the art of managing vegetation; it is especially important with closely spaced crops like cereals. Some of the cultural control methods are listed below:

9.6. Crop interference (interference may include both competition and allelopathy)

-- Selection of a competitive crop. -- Selection of a competitive variety. --Manipulation of planting arrangement and density. -- Allelopathic effects of certain crops. -- Shift to a smoother crop. -- Multiple cropping. -- Fertiliser placement. -- Timing of planting. --Liming. -- Irrigation and drainage. -- Crop rotation.

9.7. Biological control: The use of biotic organisms to control weeds, e.g. insects, mites, plant pathogens, birds and grazing animals.

9.8. Integrated weed management: Several weed control methods combined (cultural, mechanical, biological, and preventive methods) to increase effectiveness and efficiency.

9.9. Chemical control ofweeds

The use of organic and inorganic compounds to disrupt plant growth. Chemical control should not ti·equently be used alone: integration with other control methods assures a more effective result. Socio-economic and agronomic conditions will determine which methods are combined.


9.10. Possible advantages of herbicides

• Speed of control - can be used on extensive areas. • Less drudgery than manual control. • Control is possible in critical period when the weather does not allow other methods to be

used (when there is continuous rainfall). • Selective control. • Control of special weed problems. • Control in closely spaced (closed) crops. • Reduced erosion with less cultivation. • Mixtures permit broad spectrum control. • Possible economy.

9 .11. Possible disadvantages of herbicides

• Certain technical skill required. • Special equipment required. • Potential for crop injury both within and outside the target area. • May fail to kill weeds. • Not totally safe for animals or humans (potential tor envirmm1ental contamination). • Weeds may develop resistance. • May create reliance on an imported product. • Secondary weeds may become a primary problem. • Cost: limited cash and credit make it difficult for small-scale farmers to buy herbicides. • Intercrops: selectivity is a problem in intercropping systems, where several crops are

present.

9.12. Herbicide identitication

Herbicides can be identified in four possible ways:

• A chemical formula.

• A common name which begins with a small letter. Common names are given by the recognised organisations such as the British Standards Institute or the Weed Science Society of America.

• A trade name which begins with a capital letter. The trade name is given by the manufacturer as its property.

• A chemical structure.

Example:

-- chemical tormula - N-(phosphonomethyl)glycine -- conunon name- glyphosate -- trade name - Round-up


9.13. Herbicide classification

9.13 .1. Herbicide classification- by time of application

Table 9.1. Herbicide classification by time of application

Period Crop Weeds Examples

Pre-plant Pre-plant Post- Glyphosate or paraquat in no-till ·

Pre-plant Pre- Pre- EPTC in maize incorporated

Pre-emergence Pre- Pre- Atrazine in maize

Pre- Post- Atrazine in maize

Post-emergence Pre- Post- Paraquat, in no-till

Post- Post- 2,4-D Ill wheat, Propanil in rice

Post -directed Post- Post- Paraquat in maize

Source:F AO (1986) Note: Pre= before; Post= After

9.13.2. Selective (alachlor) vs. non-selective (glyphosate, paraquat). 9.13.3. Foliage acting (paraquat, propanil) vs. soil acting (atrazine, simazine). 9.13.4. Contact (paraquat) vs. translocated (glyphosate). 9.13.5. Mode of action e.g. photosynthesis inhibitors (atrazine, paraquat).


9.14. Common herbicides for weed control in maize

Table 9.2. Common herbicides for weed control in maize.

Preplant Preemergence

Alachlor Alachlor

Atrazine Atrazine

Butylate CDEC

Chlorbromuron Chloramben

Dalapon Cyanazine

Diallate 2,4-D

EPTC Diallate

Paraquat Dinoseb

Simazine EPTC

Paraquat

Propachlor

Source: Klingman, Ashton, and Noordhoff (1975).

9.15. How herbicides work

For a herbicide to be toxic to a plant, it must:

--make contact with its target (foliage or roots) -- penetrate the plant -- move to the site of action within the plant --exercise a toxic effect upon the plant's vital process

Postemergence

Ametryn

Atrazine

Cyanazine

Cyprazine

2,4-D

Dicamba

Dinoseb

Linuron

Propachlor

9.15. Prevention of the development of herbicide resistance and the build-up of nonsusceptible species

-- Rotation of crops --Rotation of weed control methods -- Rotation of herbicides --Combination ofherbicides --Integration of weed control methods

9.16. Herbicide Mixtures.

There are some advantages to herbicide mixtures. These include:

• Saves time • Reduces application costs • Mixtures have a broader spectrum of weeds controlled • May reduce application rates of each herbicide • Prevents shifts in weed population.


9.17. Sprayer calibration

The objective of sprayer calibration is to determine or adjust a sprayer's output so as to facilitate uniform distribution of an exact quantity of chemical in a given area. Excessive herbicide application can kill the crop, is costly and can cause environmental hazards. On the other hand, too little herbicide, results in poor weed control.

9.17 .1. Requirements for sprayer calibration

In order to calibrate a sprayer, factors that regulate sprayer output should be known. These include the following:

Nozzle orifice size: There is a direct relationship between orifice size and output: the larger the orifice, the greater the output.

Speed: An inverse relationship exists between travel speed and sprayer output. For example, if speed is doubled, output is reduced by 50 percent.

Pressure: Relative change in output is proportional to the square root of relative change in pressure at the nozzle. For example, in order to double output, pressure must be increased nearly fourfold.

9.17.2. Calibrating a knapsack sprayer

Before a sprayer is calibrated, check for leaks by adding water into the sprayer. Also ensure that it operates properly. There is need, therefore, to practise spraying with water until one is comfortable witl1 the operation of the sprayer.

9.17.3. Steps in calibrating knapsack sprayer

1. Because knapsack sprayers do not pwnp out all of the liquid placed in them, there is need to detennine the amount of water that cannot be sprayed out. This is done by

-Adding a measured amount of water to the sprayer, then -spray into a container of water with the nozzle held under the water surface. -Stop when large bubbles appear, which indicates that air is being pumped. - Measure the amount of water sprayed and subtract from the amount put in the

sprayer.

9.18. Determining the sprayer output (amount of water in 1/ha)

a) Add a measured amount of water (2-41) to the completely empty sprayer. b) At a comfortable walking speed and pumping rhythm, spray a measured area. c) Measure the water remaining in the sprayer (or the amount needed to refill it to the original level), and d) calculate the output in litres per hectare using the formula below:

Formula: Water used in litres x 10,000 m~ = 1/ha Area sprayed in m

9.19. Herbicide calculations

Follow this procedure to calculate the correct mix of water and herbicide to put in the sprayer:

9.19 .1. Detennine output per hectare using the formula as above:

Water used x 10,000 m~ = 1/ha Area sprayed m


Example. Area to be sprayed =200 m2

Amount of water used =3 1

The output of the sprayer is equal to

3 1 x 10,000 m~ = 150 1/ha 200 m

9.19.2. Determine the size of the area to be sprayed, then Calculate the amount of water needed to spray the desired area, as follows:

m~ to be sprayed x output in 1/ha = litres required -2 -m per hectare

Example: Area to be sprayed: 5 plots of 40 m2 each= 200 m2

Output of sprayer = 150 1

Thus the amount of water needed to spray 200 m2

200 m~ x 150 1/ha = 3 1 of water required 10, 000 m~ /ha

9.19.3. Determine the amount of active ingredients of herbicide needed to treat 1 hectare

However, most knapsack sprayers do not pump out all the liquid in the tank, pump and pressure chamber. To determine the amount of water that must be added to allow for this and for minor errors, it is necessary to account for:

a) the amount needed to spray plots= 3,000 ml b) the amount that is not pwnped out= say 450 ml (this is detennined for each sprayer) c) a margin for safety =say 200 ml (determined for each situation)

Therefore total an1mmt of water needed 3650 ml

Now the amount of commercial produce (CP) needed for the above quantity of water can be calculated as follows:

Total water in litres x Desired rate of herbicide CP = Calibrated 1/ha (output) Percent active ingredient expressed as a decimal

Example (a) Assume we want to apply the equivalent of 2.0 kg active ingredient /ha of a product containing 80% active ingredient.

Thus 3.65 1 x 2 kg = 0.0608 kg or 60.8 g. CP = 150 1/ha .80

Example (b) Assume we want to apply 3 I of the herbicide Dual per ha. The out put of the sprayer is 150 1/ha. How much dual is required to spray 6 plots of 50 m2 each?

Steps:

l. First calculate amount of water required to spray the area of the plots. Area to be sprayed = 6 x 50 m2 = 300 m2

Output = 150 1/ha

m~ to be sprayed x output in 1/ha -2

= litres required m per hectare

Thus the amount of water needed to spray 300 m2

300m~ x 150 1/ha = 4.5 I of water required 2 10,000 m /ha


2. Thus amount of dual/300m2 = 4.5 1 x 3.0 l = 0.091 or 90 mls = 150 1/ha

9.20. References

F AO. 1986. Instructor's Manual for Weed Management. FAO, Rome. Kabambe, V.H., and J.D.T. Kumwenda. 1995. Weed management and nitrogen rate effects

on maize yield and yield components in Malawi. In D.C. Jewell, S.R. Waddington, J.K. Ransom and K.V. Pixley (eds.). Maize Research for Stress Environments. Proc. of the Fourth Eastern and Southern Africa Maize Regional Conference, Harare, Zimbabwe, 28 March to 1 April, 1994. CIMMYT, Mexico.

Klingman, G.C., F.A. Ashton, L.J. Noordhoof. 1975. Weed Science: Principles and Practices. John Willey and Sons, New York.

Kumwenda, J.D.T., and V.H. Kabambe. 1995. Critical period of weed interference in pure maize, maize/soybean and maize/pigeonpea intercrops. In D.C. Jewell, W.R. Waddingoton, J.K. Ransom, and K.V. Pixely. Maize Research for Stress Environments. The Fourth Eastern and Southern Africa Maize Regional Conference. 28 March to 1 April, 1994. CIMMYT, Mexico.

Ross, M.A., and C.A. Lambi. 1985. Applied Weed Science. Burgess Publishing Company, Minneapolis.

Zimdahl, R.L. 1980. Weed-Crop Competition: A Review. International Plant Protection Center, Oregon State University, Corvalis, Oregon, USA.

10. LONG TERM STRATEGIES FOR STRIGA CONTROL

.Joel Ransom

10.1. Systems Approach

1 0.1.1. Why long term approaches in a cereal dominant system.

• Current technology only provides partial control. • Many recommendations are expensive and beyond the reach offarn1ers. • Yearly inputs may be affordable, though response is not dramatic.

1 0.1.2. Objectives of long tem1 approaches

1 0.1.2.1. Rather than increasing yield ~ se, the initial season, the objective is to reduce the Striga seed bank, in subsequent seasons. (Emphasises biology, rather than chemistry). Direction of level of infestation is more important. Use time to our advantage.

1 0.1.2.2. Treatments focus on:

• Reducing or eliminating new seed production. • Reducing or eliminating Striga seeds in the soil. • While maximising economic yields.

1 0.1.2.3. Measurements on change in level of infestation.

1 0.2. Methodology for reducing or eliminating seed production.

1 0.2.1. Hand pulling before seed dispersal

• 16-18 days between flowering and first viable seed, but additional days before the capsule dries and opens.

• Timing requirements as there is re-emergence.


-- Usually one hand weeding controls 90%+ in maize if done past flowering. --Sorghum is later than maize and may require additional hand weeding. -- Very much dependent on the environment.

1 0.2.2. Herbicide

• 2.4-D most cost efiective

• Many others including Oxyfloryfen, Paraquat, Dicamba, etc.

1 0.3. Factors which reduce Striga seed number in the soil

10.3.1. Natural demise

• Viable for up to 20 years?

• USDA use a 5-6 year life expectancy in the eradication programing the USA.

1 0.3.2. Microbial degradation.

• Seeds of StriKa are simple.

• Soils with an active biology decompose complex organic material more rapidly, including seeds.

10.3 .3. Gennination without attachment

10.3.4. Ethylene

• External applications limited by availability. • Donnancy and conditioning of Striga affect control. • Ethylene, a natural component of organic matter degradation. • Importance not known. • Favoured in anaerobic conditions.

1 0.3.5. Natural stimulants 1 0.3.6. Trap crops

• Variety and vigor can be important.

• Correlation between root density and area of stimulant effects.

• Dormancy/conditioning may affect% demise of Striga seeds.

10.3.7. Catch cropping (Susceptible host)

• Destroying the crop.

• Hand pulling within a crop.

1 0.3.8. Germination with pre- or post-attachment mortality

• Biological control with death of emerging radicle, or after emergence. • Herbicides (see previous discussion). • Hand pulling before seed dispersal (see previous discussion).

10.3 .9. Case studies on longer term management and control of StriKa.

• Effect of fertility, stover management, and hand weeding. • Effect of catch crops, their fertility, and various management practices of maize including

ethylene and hand weeding.


10.4 Experiments on Striga control

1 0.4.1. Designing the experiment

10.4.1.1. Typesoftrials • Exploratory - several factors with few levels of each. Fertiliser x intercrop x hand

weeding. • Determinative- many levels with few factors i.e. varietal screening. • Verification trial - a few treatments . • Demonstration - on-farm or on-station, 2 or 3 treatments, replications are not important. ·

1 0.4.1.2. Number of replications of treatments • Depends on trial type. • Variability in the site. • 3 to 4 commonly used. • On-farm sites can be used as replication.

1 0.4.1.3 Plot size

• Plot size affects experimental error.

• Two rows minimum.

• Large plots are required for long term trials and demonstrations.

10.4.2. Site Selection

1 0.4.2.1 Site requirements for good results.

• Uniform level of Striga (observed the previous season). • Sufficient size for the planned experiment. • Limited slope especially for long term trials. • Good co-operation from the farmer. • Easy access.

1 0.4.2.2. Uniform field sites

• Select site based on previous observations (high levels could mask variability). • Allow an artificially infested crop to shed Striga seed. Incorporate Striga and crop

residues as commonly done by the farmer.

10.4.2.3. How to artificially infest Striga

• Mix Striga seeds with very fine sand (sieves with 124-149 micron openings).

• Amount can vary, but have used 3.3 g of Striga seed per kg of soil, with an application rate of9 kg/ha (750 seedslm\

• Apply beneath the crop seed, cover and plant the crop.

1 0.5. Effect of Striga seed rate and seeding method on Striga numbers and maize yield

Method

Broadcast lOg Broadcast 20g Below maize 1 Og Below maize 20g

Striga

14 52 134 155

Maize Yield (kglha)

2,369 1,692 675 874

Regional Maize Course for Technicians, Arusha, Tanzania June I 997 - Page 78

10.6. Use of artificial infesting

• Cultivar difference related to rooting patterns may be obscured. • Selection of resistant types (large number of entries) needs good uniformity.

10.7. Evaluating treatment effects

10.7 .1. Counting • Usually 2 or 3 counts are useful. • Early counting to observe early effects. • One or more center rows • Problem includes non-linear relationship between counts and yield. • Timing effects.

I 0.7.2. StriRa dry weight • More time consuming. • Select optimal time. • Relationship with yield is variable.

10.7.3. Stri:<a severity rating • Score of 1-10, 0-9, 1-3, etc. • Evaluates the effect on the host. • Can be often confused with other stress symptoms, (i.e. N deficiency, Aluminium toxicity,

etc.). • Can be used for selecting for tolerance but not for resistance.

10.7.4. Striga seed numbers in the soil. • Seed counts after separation from the soil. • Expensive, time consuming. • Important for seed bank and longer term studies. • Weed to get tmiform sample (numerous small sample better than fewer large samples).

10.7.5. Crop Yield • For agronomic studies, a reasonable plot size is required, i.e. 2 rows 5m long. • Biomass in addition to grain yield may be desirable.

l 0.8 Management of experiments

1 0.8.1. Control of other weeds

• A number of herbicides can be used i.e. Atrazine, Primagran, etc. to control other weeds. • Hoeing early and hand weeding up until first emergence (about 6 weeks).

10.9. Collecting seed for experimental use

• 3-4 weeks after flowering, as capsules start to dry but before they open. • Dry material and grind lighting the top 1/3 of the plant and pass through sieves. Floating

oft light material and then drying can increase purity of seeds.

10.10. Striga free plots

• Fumigation, with methyl bromide at 500 kg/ha with seed packets to check efficiency. • Relatively Striga free plot and infest. • Long term hand weeding and ethylene.


Table 10.1. Effect of herbicide, rate, and maize genotype on Striga control after 8 weeks

Herbicide and rate Genotype Counts (no./plot) Stand(%)

lmazapyr 700 gm/ha IR 0 14

lmazapyr 140 gm/ha IR 0 63

Imazapyr 28 gm/ha IR 0 76

Imazapyr 70 gmlha IR 6 41

Imazapyr 14 gm/ha IR 34 80

Imazapyr 2.8 gm/ha IR 21 73

Check IR 21 76

Lmazapyr 140 gm/ha H512 0 0

lmazapyr 14 gm/ha H512 0 0

Check H512 128 64

Table.10.2. The effects of plant species on the number of Striga hermonthica seeds in the soil after 4 months of growth.

Species

Seshania seshan Leucaena divers{fhlia Croton megalacarpus Leucaena leucocephala Calliandra calothyrus Gliricidia sepium Markhamia lutea Grevillea rohusta Sorghum

LSD

'Yo of the maize check

87 84 113 134 93 186 102 202 89

15

ll. COMMON PROBLEMS IN MAIZE TRIALS

John Kumwenda and Batson Zambezi

Problems exist in implementing or managing maize trials. The most common problems that are encountered are outlined below.

11.1. Poor site selection

One of the common problem in implementing agronomy experiments is poor site selection for trials. Often times experiments are laid on sites that are very heterogeneous. The sources of heterogeneity include the following: slopes, unplanted alleys, graded areas, pits, sites that were previously planted to experiments, siting experiments on old demolished houses, pits or kraals, siting experiments on unproductive witchweed (Striga) sites. The


other source ofheterogeneity is siting experiments close to trees, poles, buildings, anthills. To avoid etTors or to minimize soil heterogeneity, all these should be avoided.

To avoid unproductive sites due to witchweed infestation, site selection should be done at the reproductive stage of maize when witch weed is also growing in the field. Also avoid siting experiments on possible Hood areas.

11 .l.l.Data tor site characterization

For soil fertility experiments, it is common practice to collect soil samples to characterize trial sites. However, soil analytical results may not be available before planting an experiment or even before yield results are ready for reporting. The researcher may not, therefore, be able to know fertility status of the site before planting. He may also not be able to compare results from different sites in the absence of site characterization data.

Such problems can partly be overcome by selecting sites when the maize crop is in the field still green. Visual observations of nutrient deficiency symptoms can aid the researcher to select sites that are low in say nitrogen, phosphorous or potassium. Problems of witch weed infestation can also be identified at the same time.

11.1.2. Fam1er selection

Some farmer managed experiments are very poorly managed. For example, farmers may weed the experiment late, or weed a few plots in a block or replicate and leave others unweeded. Some farmers may steal some cobs from some plots or harvest the trial before the researcher comes to harvest. Some of these problems may be due to selection of uncooperative farmers or farmers may become sick during the implementation of the trial. It is important farmers selected to cooperate for on-fann activities should be cooperative, and committed to doing a good job.

11.2. Land preparation for the on-farm trial site

When farmers are not given proper instructions on land preparation, they tend to burn crop residues on the trial site. Burning residues adds nutrients to the soil and can cause heterogeneity in the field plot. This operation should be avoided or avoid such spots when laying out trials.

Row width: some fanners tend to make ridges wider or narrower than rec01pmended row spacing, and sometimes ridges are not made straight. The researcher should always check the row width and row alignment and make necessary adjustments before laying out the trial.

11.3. Alleyways

Alleyways are a common component of field trials, both on-station and on-farm. Alleyways allow easier access to the inside of a trial for applying treatments and collecting data. However some researchers leave alleyways unweeded, making accessibility impossible. Also alleyways can be a source of pests or diseases if unweeded.

lf the trial is planted on ridges, ridges between alleyways should not be disturbed or broken to make highways. Such a practice may cause soil erosion.

Regional Maize Course for Technicians, A rush a, Tanzania June I 997- Page 81

11.4. Reading instructions and packing inputs

Some technicians do not plan their activities for implementing trials a head of time. For example some may not read instruction sheets until the time of laying the experiment in the tield or pack inputs on the day of laying or planting the trial. This wastes a lot of time and they may forget to carry all the materials that are required for laying or planting a trial. A technician should be committed to do good work by reading instruction sheets a head of time and should always make a calendar of events that are required for the implementation of the trial. When packing inputs for on-farm or off station trials make a list of what will be carried before packing. Input packs should also be well labeled.

ll.S. Laying out of blocks (replicates)

Laying of experiments on slopes has been a common problem of many technicians. some technicians tend to lay blocks along the slope. This means that treatments or plots within a block will be subjected to a fertility gradient.

It should be noted that the main purpose of blocking is to reduce as much as possible differences among plots within each block. Proper blocking should increase the differences among blocks while leaving plots within a block more homogeneous. Therefore it is important to know the fe1iility pattern in the experimental area.

Gomez and Gomez ( 1976) described a simple rule to follow when laying out block on slopes. That blocks should be oriented such that their length is perpendicular to the direction of the fertility gradient. For example, for a field with a gradient along the length of the field, blocking should be made across the width ofthe field, cutting across the gradient.

11.6. Border rows

Trials that need border rows (e.g. one-row plot, two-row-plot trials) are planted without any border rows, or border rows are planted later than the trial, or worse still they are planted with material or a variety that is of a different growth habit than the materials in the trial. e.g. tall variety as border rows for short inbred materials being evaluated.

11.7. Planting, weeding, data collection, application of pesticides or harvesting

It is a common practice for some research workers to assign more than one person to do an operation (e.g. planting, weeding, d::~.ta collection, etc.) in a plot in or a block so that work can be completed quickly. This results in variations in crop performance within a plot.

Except for the different treatments assigned, plots within each block should be managed as uniformly as possible. Data collection and all cultural and management practices, aside from the treatments being studied, should be made at the same time and as uniformly as possible on all plots in each block. For example, if application of fertiliser, pesticides or harvesting of a field experiment must be done over several days, all plots in a block should be applied or harvested in the same day. Also if more than one research worker make observations on the experimental area and if there is any likelihood that observations made on the same plot would differ with individual, then different persons should be assigned to different blocks; i.e. one person should make the observations for all plots in a block.

11.8. Time of data collection

Timing is crucial for such data as days to 50% silking and 50% pollen shed. Data must be recorded every day, if possible, or at least every other day until all the plots are complete.


When scoring for diseases, it is essential to know that certain maize diseases such as leaf blight and rust tend to be more severe towards the end of the season. Scoring too early may give the impression that the genotypes are resistant, if one scores too late, the leaves will be dry and it will be difficult to separate physiological leaf drying from that caused by leaf diseases.

11 .8 .1. Plant height, e.g. in some instances one may measure from ground level to the flag leaf~ in another instance one may measure from the ground level to the first tassel branch. The bottom line is to read instructions first before undertaking any activity so as to understand what instructions are given in the field book for any particular parameter.

11.8.2. Disease scoring. There are different scales that researchers use for disease scoring. Some use the scale of 1-5, others 1-9, etc. It is therefore, important to read instructions to establish what scale for any particular disease is required. If you are not familiar with the disease or insect pest incidence please ask for assistance, or leave it out.

11.9. Mismatching labels or stealing labels

Lt is very common for on-farm trials to have labels stolen (especially metal labels) or mismatched by kids during weeding operations. It is important to make a map of the trial location and field plan. Because plot labels can be stolen or mismatched, always work from the field plan when applying treatments.

11.10. Transfer of records.

In certain situations recorders enter field records in pocket notebooks and then transfer the information later (usually after harvest) into the field books. Unfortunately this could lead to loss of valuable data. lt is often too late to go back to the field to take fresh data. It is strongly recommended that data be entered directly into the field books at the time of data collection. It does not matter if the field book is dirty because of muddy field conditions. It is better to have a dirty field book with accurate data than a spotless clean field book with wrong or missing data. This could also create the temptation by the recorder to "cook" data to replace the lost information.

11.11. Data dispatch

Some cooperating researchers send data to the principal scientists by post without keeping a copy of the data. When data are lost in the post, data can not be recovered. AI ways keep a copy of the data when sending by post.

11.12. Over delegation

Some researchers (Technicians) over delegate their work to skilled laborers. This should be avoided because skilled laborers make a lot of mistakes as they are not trained.

12. GLOSSARY OF PLANT BREEDING TERMS

Z. Mduruma, N. Lyimo and H. Akonaay

Anther: The pollen-bearing portion of the stamen.

An thesis: The process of dehiscence of the anthers; the period of pollen distribution.

Breeder Seed: Seed (or vegetative propagating material) increased by the originating or sponsoring, plant breeder or institution, used as the source for the increase of Foundation Seed.


Character: The expression of a gene as revealed in the phenotype.

Chromosome: Structural unit in the nucleus which carries the genes in a linear constant order, it preserves its individuality from one cell generation to the next and is typically constant in number in any species.

Combining Ability, General: The average or over-all performance of genetic strain in a series of crosses.

Combining ability, Specific: The performance of specific combinations of genetic strains in crosses in relation to the average performance of all combinations.

Composite: A mixture of genotypes from several sources, maintained by normal pollination.

Cultivar: Synonymous with variety; the intemational equivalent of variety.

Detassel: Removal of the immature tassel as practiced in the production ofhybrid seed com.

Di-hybrid: The result of a cross between parents which differ by two specified genes.

Dominant: (a) A gene that expresses itself in a hybrid to the exclusion of its contrasting (recessive) allele; (b) a character which is expressed in a hybrid phenotype to the exclusion of the contrasting (recessive) character.

Dominant Gene Effects: Gene action with deviations from the additive such that the heterozygote is more like one parent than the other.

Double Cross: (a) A cross between two single crosses; (b) the Fl progeny of a cross between two single crosses.

Embryo: The rudimentary plant in a seed. The embryo arises from the zygote.

Embryo Sac: Typically, an eight-nucleate female gametophyte. The embryo sac arises from the megaspore by successive mitotic divisions.

Endosperm: Triploid tissue which arises from the triple fusion of a spem1 nucleus with the polar nuclei of the embryo sac. In seeds of certain species, the endosperm persists as a storage tissue and is used in the growth of the embryo and by the seedling during gennination.

Evolutionary Breeding: breeding procedure in which the variety is developed from an unselected progeny of a cross, or multiple crosses, that have undergone evolutionary changes.

Fertilisation: [s the union of an egg with a sperm from the same t1ower or from another flower on the same plant, or within a clone.

Cross Fertilisation: is the union of an egg with a sperm from a plant of a different clone.

Foundation Seed: Seed stocks increased from Breeder Seed, and so handled as to closely maintain the genetic identity and purity of a variety. Foundation Seed is the source of Certified Seed, either directly or through Registered Seed.

Gene: The unit of inheritance, located on the chromosome; by interaction with other genes, the cytoplasm, and the environment, it affects or controls the development of a character.

Gene Interaction: Modification of gene action by a non-allelic gene.

General Resistance: Nonspecific host plant resistance.

Genetics: The science dealing with heredity.


Genome: A set of chromosomes, such as contained within a gamete; corresponds to the haploid number of chromosomes within a diploid species.

Genotype: (a) The genetic makeup of an organism- the sum total of its genes, both dominant and recessive; (b) a group of organisms with the same genetic make-up.

Germplasm: (a) The material basis of heredity; (b) the potential hereditary material within a species, taken collectively.

Germplasm Collection: A collection of genotypes of a particular species, from different sources and geographic locations, used as source materials in plant breeding. (Also, see World Collection).

Heredity: The transmission of genetic characters from parents to progeny; the genetic characters transmitted to an individual by its parents.

Heritability: Capability of being inherited; that portion of the observed variance in a progeny that is inherited.

Heritability, Broad Sense: Heritability estimated from the total genetic variance.

Heritability, Narrow Sense: Heritability estimated from the additive portion of the genetic vanance.

Heterosis (Hybrid vigor): (a) the increased vigor, growth, size, yield or function of a hybrid progeny over the parents that results fi·om crossing genetically Lmlike organisms; (b) the increase in vigor or growth of a hybrid progeny in relation to the average of the parents.

Heterozygous: Having unlike alleles at corresponding loci of homologous chromosomes. An organism may be heterozygous for one, or several genes. (See also Homozygous).

Homozygous: Having like genes at corresponding loci on homologous chromosomes. An organism may be homozygous for one, several, or all genes. (see also Heterozygous).

Hybridise: To produce hybrids by crossing individuals with different genotypes.

Hybrid Vigor: See Heterosis.

Immune: Free from attack by a given pathogen; not subject to the disease.

Inbred Line: (a) A pure line usually originating by self-pollination and selection; (b) the product of inbreeding.

Inbreeding: Breeding closely related organisms; in plants, usually by self-pollination. (Also, by sib-pollination, backcrossing).

Incompatibility: Failure to obtain fertilisation and seed formation after self pollination, usually due to failure of pollen tube to penetrate the stigma, or to reduced growth ofthe pollen tube in the stylar tissue.

Inherit: Receiving from one's predecessors. In organisms, chromosomes and genes are transmitted from one generation to the next.

lsolines: Lines which are genetically similar except for one gene.

Landrace: Early cultivated forms of a crop species, evolved from a wild population.

Lemma: The lower of the bracts enclosing each floret in the grass spikelet.


Line: A group of individuals from a common ancestry. A more narrowly defined group than a strain or variety.

Lodging: The bending or breaking-over of a plant before harvest.

Lodicule: One of two scale like structures at the base of the ovary in a grass flower.

Mass Selection: A system of breeding in which seed from individuals selected on the basis of phenotype is composited and used to grow the next generation.

Modified Single Cross: The progeny of a cross between a single cross, derived from two related inbred lines, and an unrelated inbred line.

Monoecious: Having staminate and pistillate flowers on the same plant.

Monohybrid: The result of a cross between parents which differ by one specified gene.

Monosomic: An organism lacking one chromosome of a diploid complement.

Multiple Variety: A composite of isolines.

Multiple Alleles: A series of alleles, or alternative forms, of a gene. A normal heterozygous diploid plant would bear only two genes of an allelic series. Multiple alleles arise by repeated mutations of a gene, each mutant giving different effects.

Multiple Genes: Two or more genes at different loci which produce complementary or cumulative effects on a single quantitative genetic trait. (Also Polygenes).

Mutant: An organism which has acquired a heritable variation as a result of mutation.

Non-Preference: Plant resistance to insects through suppression of feeding or oviposition.

Non-Recurrent Parent: Parent not involved in a backcross. Also Donor Parent. (See also Reccurent Parent).

Open Pollinated: Natural cross pollination.

Outcross: Cross-pollination, usually by natural means, with a plant differing in genetic constitution.

Ovary: The enlarged basal portion of the pistil, in which the seeds are borne.

Ovule: The structure which bears the female gamete and becomes the seed after fertilization.

Palea: The upper of the bracts enclosing each floret in the grass spikelet.

Pathogen: An organism capable of inciting a disease.

Pedigree Selection: Selection procedure in a segregating population in which progenies of selected F2 plants are reselected in succeeding generations until genetic purity is reached.

Perfect Flower: Flower possessing both stamens and pistils.

Phenotype: (a) Physical or external appearance of an organism as contrasted with its genetic constitution (genotype)~ (b) a group of organisms with similar physical or external makeup.

Phenotype Ratio: The proportions of the different phenotypes in a particular progeny.

Pistil: The seed-bearing organ in the flower composed of the ovary, the style, and the stigma.

Pistillate Flower: A flower bearing pistils but no stamens.


Plant Introduction: (a) transport of a collection of seeds, plants, or vegetative propagating materials from one ecological area to another; (b) collection of seeds, plants or vegetative propagating materials which have been transported from one location to another.

Polar Nuclei: Two centrally located nuclei in the embryo sac which unite with the second sperm in a triple fusion. In certain seeds the product of this triple fusion develops into the

endosperm.

Pollen Grain: The male gametophyte, originating from a microspore.

Pollen Mother Cell: See Microspore Mother Cell.

Pollen Tube: A tube developing from the germinating pollen grain. The sperm cells pass through the pollen tube to reach the ovule.

Pollination: Transfer of pollen from the anther to a stigma.

Self-Pollination: The transfer of pollen from an anther to the stigma of the same flower or another flower on the same plant, or within a clone. Cross-Pollination: is the transfer of pollen from an anther of one plant to the stigma of a flower on a different plant or clone.

Progeny Selection: Selection based on progeny perfom1ance.

Progeny Test: A progeny, or groups of progenies, grown for the purpose of evaluating the genotype of the parent.

Pure Line: A strain in which all members have descended by self-fertilization from a single homozygous individual. A pure line is genetically pure (homozygous).

Purity: With reference to sugar beets, the ratio of sucrose to total solids dissolved in sugar beet juice.

Reciprocal crosses: Two crosses between two plants or strains in which the male parent of one cross is the female parent of the second cross for example, A x B and B x A.

Recombination: Formation of new gene combinations as a result of cross-fertilization between individuals differing in genotype.

Recurrent Parent: Parent to which hybrid material is crossed in a backcross. (See also NonRecurrent Parent).

Recurrent Selection: A breeding system designed to increase the frequency of favorable genes of a quantitatively inherited characteristic by repeated cycles of selection.

Registered Seed: The progeny of Breeder or Foundation Seed and so handled as to closely maintain the genetic identity and purity of a variety. Registered Seed is the source of certified seed. Registered seed must be approved and certified by an official seed certification agency.

Resistance: Characteristic of a host plant such that it is capable of suppressing or retarding the development of a pathogen or other injurious factor.

S: Symbol used to designate the original selfed plant.

sl, s2 etc.: Symbols for designating first selfed generation (progeny of SO plant), second selfed generation (progeny of S 1 plant), etc.

Seed: A mature ovule with its normal coverings. A seed consists of the seed coat, embryo, and, in certain plants, an endosperm.

Regional Maize Course for Technicians, Arusha, Tanzania June 1997 - Page. 87

Segregation: The separation of homologous chromosomes (and genes) from different parents at meiosis.

Selection: (a) any process, natural or artificial which pennits an increase in the proportion of certain genotypes or groups of genotypes in succeeding generations; (b) a plant, line, or strain which originated by a selection process.

Sexual Reproduction: Reproduction involving germ cells and union of gametes.

Spikelet: A w1it of the inflorescence in the grasses, composed of the glumes, the rachilla, and the florets.

Stamen: The pollen-bearing organ in the flower; composed of an anther and a filament.

Stamin~te Flower: A flower bearing stamens but no pistil.

Stigma: The portion of the pistil which receives the pollen.

Style: The stalk connecting the ovary and the stigma.

Susceptible: Characteristic of a host plant such that it is incapable of suppressing or retarding an injurious pathogen or other factor. SYN0, SYN1, SYN2, etc.: Symbol for designating the original synthetic population, first synthetic generation (progeny of Syn1), etc.

Synthetic Variety: Advanced generations of open-pollinated seed mixtures of a group of strains, clones, or inbreds, or of hybrids among them.

Test cross: A cross of a hybrid with one of its parents, or to a genetically equivalent homozygous recessive. Used to test for homozygosity or for linkage.

Three-Way Cross: The progeny of a cross between a single-cross and an inbred line or pure line variety.

Tolerance: Ability of plants to survive in presence of destructive pathogen, insect, or enviromnental condition.

Topcross: An outcross of selections, clones, lines, or inbreds, to a common pollen parent. In com, commonly an inbred-variety cross.

Top-Cross Progeny: Progeny from outcrossed seed of selections, clones, or lines to a common pollen parent.

Transgressive Segregation: Segregation of genotypes, in the F2 or at a later generation of a cross, which show a more extreme development of a character than either parent.

Tri-Hybrid: Resulting from a cross between parents which differ by three specified genes.

Variety: A subdivision of a species. An agricultural variety is a group of similar plants which by structural features and performance can be identified from other varieties within the same species. (Also, see Cultivar).

Variety Blend: Mechanical mixture of seed of two or more varieties.

World Collection: Synonymous with germplasm collection. (Also see Germplasm Collection).

Zygote: The cell resulting from the fusion of gametes.


13. ACKNOWLEDGMENTS

I would like to convey my sincere thanks to the resource persons listed below, for the excellent materials they prepared and presented at the course. I also thank the participants for their keen interest in the course. I appreciate, very much, the cooperation of the Tanzanian National Program for hosting as well as participating in the course; similarly for National Programs of Malawi, Zambia and Zimbabwe for making their technicians available for training.

Herman B. Akonaay, Maize Breeder, Selian Agricultural Research Institute, P.O. Box 6024, Arusha, Tanzania.

John

Nick

Tel: (255)-57-3883, Fax. (255)-57-8242 Email: <[email protected]>

D.T. Kumwenda, Chief Agrictlltural Scientist for Cereal crops and Maize Agronomist, Chitedze Agricultural Research Station, P.O. Box 158, Lilongwe, Malawi. Tel: (265)-767222/225/252, Fax. (265)-782835 c/o Rockefeller Foundation.

G. Lyimo, Maize Breeder, Ministry of Agricultural Research and Training Institute (MARTI), Uyole, P.O. Box 400, Mbeya, Tanzania.

Zubeda 0. Mduruma, Maize Breeder and Team Leader, Selian Agricultural Research Institute, P.O. Box 6024, Arusha, Tanzania. Tel: (255)-57-3883, Fax. (255)-57-8242. Email: <[email protected]>

Joel K. Ransom, CIMMYT, P.O. Box 25171, Nairobi, Kenya. Tel: (254)-2-632054/632206, Fax.: (254)-2-630164. Email: [email protected]

This course was conducted with financial assistance ffom the 'Maize and Wheat Improvement Research Network for SADC' (MWIRNET) under the auspices of Southern African Center for Cooperation in Agricultural Research (SACCAR). CIMMYT is the executing agency for MWJRNET and funding from the European Union for this network is gratefully acknowledged.


Annex 1. Course Evaluation

REGIONAL MAIZE TRAINING COURSE FOR TECHNICIANS FROM MALAWI, TANZANIA, ZAMBIA AND ZIMBABWE: ARUSHA, TANZANIA, JUNE 1-11, 1997

Total number of participants =

25 Overall Evaluation

A Course aspect Participants' majority comments response ('%)

Course content was very useful 24 96 Useful I not useful 0

2 Course organization well organized 19 76 poorly organized 6

" Course duration too long 0 _,

just right 12 too short 13 52

4 Would you recommend yes 23 92 such a course to a friend no 2

5 Course objective achieved 23 92 not achieved 2

B Subjects covered very useful useful interesting neither majority

but not interesting response useful nor (%)

useful Population improvement 20 3 2 0 80

2 The maize plant 12 8 4 48 " Hybrid production 20 3 I 1 80 _,

4 Fertilisers 16 8 0 64 5 Seed production 19 4 2 0 76 6 Exercises on fe1tilisers 16 5 2 2 64 7 Activities of MWIRNET 15 4 6 0 60 8 Hybrids vs OPVs 20 4 0 80 9 Weed control I 5 6 " I 60 _,

10 Exercises on herbicides 13 8 4 0 52 II Principles and objectives

of maize breeding 18 5 I 72 12 Common mistakes in trials 14 9 2 0 56 13 Management of trials 18 6 0 72 14 Management of Nurseries 19 5 0 76 15 Discussion on management

oftrials and nurseries 15 8 2 0 60 16 Experimental designs 16 5 2 2 64


B Subjects covered very useful useful interesting neither majority

but not interesting response useful nor (%)

useful 17 Data collection and

management 19 5 0 76 18 Scoring for disease and

pest damage 16 7 I 64 19 Grain moisture determination 17 6 2 0 68 20 Discussions on data

collection 14 8 3 0 56 21 Slide show on diseases 12 II 2 0 48 22 Striga control 9 12 4 0 36 ?" _ _, Discussions on diseases /pests II 12 I 44


Annex 2. List of Participants

REGIONAL MAIZE TRAINING COURSE FOR TECHNICIANS FROM MALA WI, TANZANIA, ZAMBIA AND ZIMBABWE: ARUSHA, TANZANIA, JUNE 1-11, 1997

List of Participants and Resource Persons

Participants

Country Name Title Contact Address

1. Malawi Mr. Mike 0. Baluti Senior Field Chitedze Agricultural Assistant Research Station, P.O.

Box 158, Lilongwe, Malawi

2. Malawi Mr. Paul N. Banda Field Assistant Baka Research Station, P.O. Box 97,Karonga, Malawi.

., Malawi Mr. Paul A. Gowa Field Assistant Bvumbwe Research ..),

Station, P.O. Box 5748, Limbe, Malawi.

4. Malawi Mr. Devlin J. Moyo Senior Field Mbawa Research Assistant Station, P.O. Box 8,

Embangweni, Mzimba, Malawi.

5. Malawi Mrs. Madalo G. Field Assistant Chitedze Agricultural Thangata Research Station, P.O.

Box 158, Lilongwe, Malawi.

6. Tanzania Ms. M. Israel Agricultural Selian Agricultural Field Officer Research Institute,

P.O. Box 6024, Arusha, Tanzania.

7. Tanzania Mr. Gonzaz K. Agricultural Selian Agricultural Kazimoto Field Officer Research

Institute, P.O. Box 6024, Arusha, Tanzania.

8. Tanzania Ms. Agripina Agricultural ARI-Katrin, Private Bag Liampawe Field Officer Ifakara, Morogoro,

Tanzania. 9. Tanzania Mr. V. Mazige Agricultural RTI-Ukiriguru, P.O.

Field Officer Box 1433, Mwanza, Tanzania.

1 0. Tanzania Ms. Christine F. Agricultural ARTI-Ilonga, P.O. Mbuya Field Officer Ilonga, Kilosa,

Morogoro, Tanzania.


11. Tanzania Mr. R.S. Mnunduma Agricultural ARI-Tumbi, P.O. Box Field Officer 306, Tabora, Tanzania.

12. Tanzania Mr. Godfrey Mwembe Agricultural ARI-Katrin, Private Bag Field Officer Ifakara, Morogoro,

Tanzania.

13. Tanzania Mr. Timotheo D. Agricultural Selian Agricultural Semuguruka Field Officer Research Institute, P. 0.

Box 6024, Arusha, Tanzania.

14. Tanzania Mr. Mohammed I. Agricultural ARTI-Ilonga, P.O. Shemahonge Field Officer Ilonga, Kilosa,

Morogoro, Tanzania.

15. Tanzania Mr. Alinanine Y. Agricultural MARTI-Uyole, P.O. Shimwela Field Officer Box 400, Mbeya,

Tanzania.

16. Zambia Mrs. Christetta M. Senior Agricultural Agriculture Research, Chimuka Res. Technician Kabwe, Zambia

17. Zambia Ms. Fanny Kamuna Agricultural Golden Valley Research Research Trust, c/o Mt. Makulu Technician Research Station, P.

Bag 7, Chilanga, Zambia.

18. Zambia Mr. George Kanga Agricultural Golden Valley Research Research Center, P. Box 54, Technician Fringilla, Zambia.

19. Zambia Mr. Jesper Longwe Agricultural Msekera Research Research Station, P.O. Box Technician 510089, Chipata,

Zambia.

20. Zambia Ms. Hildah Nampelwe Agricultural Golden Valley Research Research Center, c/o Mt. Makulu Technician Research Station, P. Bag

7, Chilanga, Zambia.

21. Zimbabwe Mr. Joshua Dziva Agricultural Agronomy Inst., Mlezu Assistant Agricultural College, P.

Bag 8062 K wekwe, Zimbabwe.

22. Zimbabwe Ms. Nelia Ganganiso Agricultural Chisumbanje Assistant Experiment

Station, Chiredzi, Zimbabwe.


23. Zimbabwe Mr. Justin Gonye

24. Zimbabwe Mr. Ezekiel Goronga

25. Zimbabwe Toughnety Pindirire

Resource Persons

1. Malawi Dr. John D.T Kumwenda

2. Tanzania Mr. Herman Akonaay

3. Tanzania Dr. Nick G. Lyimo

4. Tanzania Dr. Zubeda 0. Mduruma

5. CIMMYT Dr. Joel K. Ransom (Kenya)

Course Coordinator

Dr. Batson T. Zambezi

Agricultural Supervisor

Agricultural Assistant

Agricultural Assistant

Chief Agricultural Research Officer and Maize Agronomist

Maize Breeder

Maize Breeder

National Maize Program Team Leader and Maize Breeder

Crop Breeding Inst., P. Bag 376 B, Harare, Zimbabwe.

Crop Breeding Inst., P.O. Box CY550, Causeway, Harare Zimbabwe.

Crop Breeding Inst., P.O. Box CY550, Causeway, Harare Zimbabwe.

Chitedze Agricultural Research Station, P.O. Box 158, Lilongwe, Malawi.

Selian Agricultural Research Institute, P.O. Box 6024, Arusha, Tanzania.

MARTI-Uyole, P.O. Box 400, Mbeya, Tanzania.

Selian Agricultural Research Institute, P.O. Box 6024, Arusha, Tanzania.

Maize Agronomist CIMMYT-Kenya, P.O.

Maize Breeder

Box 25171, Nairobi, Kenya.

Maize and Wheat Improvement Research Network for SADC, ClMMYT, P.O. Box MP 163, Mt. Pleasant, Harare, Zimbabwe.


Annex 3. Course Time Table

REGIONAL MAIZE TRAINING COURSE FOR TECHNICIANS FROM MALA WI, TANZANIA, ZAMBIA AND ZIMBABWE: ARUSHA, TANZANIA, JUNE 1-11, 1997.

Program of Activities

Saturday and Sunday (May 31/June 1) Arrival of participants and registration.

Monday June 2

0800-0815

0815-0830

0830-0900

0900-0930

0930-1030

1030-1130

1130-1230

1230-1330

1330-1430

1430-1530

1530-1600

1600-1700

Chair: Z. Mduruma - introduction and welcome remarks.

Brief remarks by MWIRNET Team Leader Dr. George Varughese

Official opening by Guest ofHonor, Dr. R.V. Ndondi on behalf of Zonal Director, North

Tea/coffee break

Collaboration of MWIRNET with NARS BTZ

Principles and objectives of maize breeding BTZ

The maize plant HBA

Lunch break

Hand pollinations HBA

Hybrid production methods NL

Tea/coffee break

Hybrid production methods NL

Tuesday June 3

0800-0900

0900-1000

1000-1030

1030-1130

1130-1230

1230-1330

1330-1430

1430-1530

1530-1600

1600-1700

Hybrid production - pedigree method NL

Hybrid vs. OPVs NL

Tea/coffee break

Fertilisers JDTK

Fertilisers JDTK

Lunch break

Seed production and maintenance of breeder seed HBA

Seed production and maintenance of breeder seed HBA

Tea/coffee break

Exercises on fertilisers JDTK

Wednesday June 4

0800-0900

0900-1000

Population Improvement ZOM

Population Improvement ZOM


1000-1030 Tea/coffee break

1030-1130 Weed control JDTK

1130-1230 Weed control - herbicide use JDTK

1230-1330 Lunch break

1330-1430 Population Improvement ZOM

1430-1530 Types of OPV s ZOM


1600-1700 Exercises on herbicides JDTK

Thursday June 5

0800-1000

1000-1030

1030-1130

1130-1230

1230-1330

1330-1430

1430-1530

1530-1600

1600-1700

Friday June 6

Discussions on: hybrid production, the maize plant, population improvement, fertilisers, and weed control. BTZ

Tea/coffee break

Management of trials- seed preparation, labeling (to prevent mixtures), importance of border rows and germplasm for border rows NL

Laying out field trials, importance of uniformity in handling trials ZOM

Lunch break

Seedbed preparation, planting; planting patterns (plant densities) HBA

Harvesting trials, shelling, etc. ZOM

Tea/coffee break

Harvesting of nurseries, storage of seed, etc. NL

0800-0900 Data collection and management, why collect data? plant stand, lodging (root and stem), days to 50% silking/pollen shed, plant and ear height (how to measure and sampling) ZOM

0900-1000 Disease and pest scoring techniques, ears/plant (measure of prolificacy) ear rot scores NL


1 030--1130 Exercises on grain yield determination, calculation of yield per hectare corrected to a given grain moisture, calculation of lodging percent, etc. HBA

1130-1230 Striga control JKR

1230-1330 Lunch break

1330-1430 Striga control JKR

1430-1530 Exercises on calculations: % lodging, grain yield conversions, etc. HBA


1600-1700 General discussion on data collection, etc. BTZ


Saturday June 7 Free for shopping, site seeing, etc.

Sunday June 8 Free

Monday .June 9

0800-1230

1230-1330

1330-1530

1530-1600

1600-1700

Field exercises: hand pollinations, silking /pollen shed records, etc.

Lunch break

Discussions on field exercises.

Tea/coffee break

Discussions ( cont' d)

Tuesday June 10

0800-1230

1230-1330

1330-1530

1530-1600

1600-1700

Field exercises: rating for disease and insect damage.

Lunch break

Discussions on field exercises.

Tea/coffee break

Discussions ( cont' d)

Wednesday June 11

0900-1000

1000-1030

1030-1100

1400

Wrap up sessions: discussions on pa1iicipants' views on the course and their activities in their respective national programs.

Course evaluation

Closing: ZOM

Departure of participants: Those from Malawi, Zambia, and Zimbabwe boarded the 1400 hours Arusha-Nairobi bus shuttle.


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