GENETIC Deterioration of varieties

1.Developmental variation

2.Mechanical mixture

3.Mutation

4.Natural Crossing

5.Minor Genetic Variation

6. Selective Influence of Diseases

7.The Techniques of the Plant Breeder

Maintenance of genetic purity

AGRONOMIC

Selection of a Agro-climatic Region

Selection of seed plot Isolation of Seed crops Preparation of Land Selection of variety Seed treatment Seed plantation Farm operations Harvesting of seeds After harvest care

1. Developmental variation2. Mechanical mixture3. Mutation4. Natural Crossing5. Minor Genetic Variation6. Selective Influence of Diseases7. The Techniques of the Plant Breeder

Arise when seeds are grown in: Difficult environment

Different soil & fertility conditions

Different climatic conditions

Different photo-periods

Different elevationsFor several consecutive generations Solution:Grow them in their areas of adaptation & growing

season.

Most important source of variety deterioration Take place: At sowing time if more than 1 variety is sown with

same drill

During harvesting& threshing operations.

Gunny bags, seed bins, elevators etc are contaminated with seeds of other varieties.

Solution: Rogue the seed fields

Care during seed production, harvesting, threshing & further handling.

Not a serious factor.

Difficult to detect minor mutations.

Solution:

Remove mutant plant

Increase of true to type stock eliminate the problem

Most important source deterioration The deterioration in variety due to natural

crossing occurs due to the following 3 reasons:- Natural crossing with undesirable type. Natural crossing with diseased plant Natural crossing with off-type plants

In self fertilized crops, natural crossing is not a serious source of contamination & variety deterioration unless:

The variety is male sterile Grown in close proximity to other varieties.

But in Cross fertilized crops, natural crossing is the major source of genetic contamination.

Genetic contamination in seed fields due to natural crossing depends upon the following factors: The breeding system of species Isolation distance Varietal mass Pollinating agent

Solution: Isolation between plantation. Small amounts of contamination over wide distances.

Exist in the phenotypically uniform & homogenous varieties at the time of their release.

During later production of cycle variation lost due to selective elimination by environment.

Solution: Yield trials of lines propagated from plants of

breeder’s seed in the maintenance of self fertilized crop varieties.

Care during maintenance of nucleus & breeder’s seed is necessary.

New crop varieties often become susceptible to new races of diseases

Vegetatively propagated stocks deteriorate

Solution:

During seed production it is very necessary to produce disease free seeds/stocks.

Premature release of variety

Variety testing program

Break down in male sterility

Environmental conditions

Heritable variation

Solution: Careful handling and adaptation of

techniques

Use of approved seed only in seed multiplication.

Inspection & approval of fields prior to planting.Field inspection & approval of growing crops at

critical stages for verification of genetic purity, detection of mixtures, weeds and for freedom from noxious weeds & seed borne disease Etc.

Sampling & sealing of cleaned lots.Growing of samples of potentially approved

stocks for comparison with authentic stocks.

Providing adequate isolation to prevent contamination by natural crossing or mechanical mixtures.

Roguing of seed fields prior to the stage at which they could contaminate the seed crop

Periodic testing of varieties for genetic purity.Avoiding genetic shifts by growing crops in areas

of their adaptation only.Certification of seed crops to maintain genetic

purity & quality of seed.Adopting the generation systemGrow out test.

Seed production is restricted to four generations only

Starting from breeder’s seed, the seed can only be multiplied up-to 3 more generations

i.e. Foundation, Registered & certified

1. Control of seed source2. Preceding crop requirements3. Isolation4. Rouging of seed fields5. Seed certification6. Grow-out test

Association of Official Seed Certifying Agencies (AOSCA) recommended 4 classes of seeds

1. Breeder’s Seed2. Foundation Seed3. Registered Seed4. Certified Seed

Breeder’sSeed:

Directly controlled by the original breeder, sponsoring breeder or institution and which provides for the initial & recurring increase of foundation seed.

Foundation Seed:

Include seed stock so handled as to most nearly maintain specific genetic identity & purity and that may be designated of distributed by an agricultural experiment station.

It is the source of all certified seeds, either directly or through registered seed

Registered Seed: It is progeny of foundation or registered seed

It is so handled as to maintain satisfactory genetic identity & purity and that has been approved and certified by a certifying agency.

This class of seed should be of a quality suitable for production of certified seed

Certified Seed: It is progeny of foundation, registered or certified

seed that is so handled to maintain satisfactory genetic identity & purity and that has been approved & certified by certifying agency.

Fixed to avoid contamination through volunteer plants & also the soil borne diseases

From contamination. Natural contamination: (cross pollination) Other contamination may be due to

mechanical mixture at Harvesting Sowing Threshing Processing Handling Soil

The removal of off type plants is referred to as rouging

There are three main sources of off type plants. Firstly the off type plants may arise due to presence of

some recessive gene in homozygous conditions at the time of release

Another source of off type plants is the volunteer plants arising from accidentally planted seeds or from seed produced by earlier crops.

Mechanical mixtures is also source of contamination. Removal is necessary before pollination occurs Regular supervision by trained personnel is

imperative.

The principal objective of seed certification is to maintain & make available crop seeds which are of good seeding value and true to variety.

Qualified & well experienced inspection is necessary.

Seed standards are confirmed by such agencies.

Varieties being grown for seed productionshould periodically be tested for geneticpurity by grow-out tests, to make sure thatthey are being maintained in their true form

Variety should be adapted to photoperiod and temperature of that area

Moderate rainfall and humidity is good for seed production

Dry sunny period and moderate temperature for pollination

General regions with extreme summer heat & very cold winters should be avoided for seed production.

Ample sunshine, relatively moderate rainfall & the absence of strong winds

Seed plot should have following characters: Soil texture & fertility should be according to the

requirement of the seed crops.

Should be free from volunteer plants, weed plants & other crop plants.

The soil should be comparatively free from soil-borne diseases & insect pests.

In the preceding season the same crop should have not been grown on this land, if it is so required by seed certification standards

Done by providing distance between seed fields & contaminating field

On a small scale i.e. in nucleus/breeder’s seed production the isolation can also be provided by enclosing plants in cage by enclosing individual flowers or by removing male flower part and then by individual artificial pollination.

After harvesting isolation of seed produced of different varieties is necessary to avoid mechanical contamination.

Similarly bags or other containers used to hold the seed must be carefully cleaned to remove any seed which may have remained in the bags from previous lots.

The land for seed crop must be prepared well. Good land preparation helps improved

germination, good stand establishment & destruction of potential weeds.

It also aids in water management & good uniform irrigation.

a)The variety should be adapted to agro-climatic conditions of the region.

b)The variety should really be high yielder.c)The variety should posses other desirable

attributes, namely disease resistance, earliness, grain quality.

Chemical seed treatment. Seed treatment for breaking dormancy due

to hard seediness

The seed crops should invariably be sown at their normal planting time.

Depending upon incidences of disease & pests, some adjustments could be made if necessary.

At time of planting there should be sufficient soil moisture for germination to take place.

Lower seed rates than usual for raisingcommercial crop are desirable because theyfacilitate rouging operations & inspection ofseed crop

Row method of sowing Mechanical drilling can be used Desired amount Uniform depth Clean equipments Proper distance between plants

Shallow plantation in case of small seeds Deep plantation in case of large seeds Deep plantation in dry soils

It is wise to remove the whole plant and not just the flower head.

The no. of rouging necessary will vary with the crop, cleanness of planting seed & stage of the multiplication of the seed crop.

Rouging in most of the field crops may be done at any of the following stages as per needs of the seed crop.a)Vegetative /pre-flowering stageb)Flowering stagec)Maturity stage

Honey bee Insects Wind and water

a)The presence of weed seeds at time of crop harvest leads to mixing of weed seeds with crop seeds. In many instances it is difficult to remove them during the processing of seeds.

b)The presence of weeds in the seed field or nearby areas may serve as host to no. of diseases. Good & effective weed control therefore would be necessary to obtain good seed yields & to avoid contamination

If systematic diseases agents are not checked the seed produces will get infected with spores of disease and produce diseased plants in the next season.

Agents of systemic disease, leave their spores on seed coats. If not checked this results in a greater susceptibility to various seedling diseases which can affect the crop.

Seed yield & quality are reduced.Management of diseases & pests in seed crops:-a)Plant only treated seedb)Prepare & adopt appropriate schedule of spraying for

effective disease &insect control.c)Roguing of diseased plants & ear heads from time to time

also helps in checking the further spread of diseases.

Nitrogen, phosphorous potassium & several other elements play an important role for proper development of plants & seeds.

Identify the nutritional requirement of seed crops & apply adequate fertilizer

Results in maximum yields, god seed quality & better expression of plant type which facilitate rouging & there by helps in maintaining higher genetic purity as well.

Dried regions are more suitable for good quality, disease free seed production in that condition irrigation is essential to obtain good seed yields.

Before planting & at intervals up to flowering.

One or two irrigations beyond flowering are desirable for may seed crop.

In general lighter soils need more irrigation than heavier soils.

Optimum time of harvest is when seed is fully mature

When weather damage begun, seed is easily harvested & cleaned resulting in minimum harvest losses.

Earlier harvesting makes combining difficult & relative losses due to threshing & cleaning are greater.

Late harvesting result in increased weather damage & losses due shattering seeds & lodging of plants in field.

By hands Quality of seed depends upon handling of

harvested crop & the care taken during threshing

Maintain lot identity My be by machine

More moisture at the time of harvest Precautions for seed drying

a)Identity of the lots must be maintained

b)Care should be taken to ensure that mechanical mixture does not take place

c)Drying of seeds to safe moisture limits should be done rather quickly.

If the seeds are to be artificially dried they should be supplied to processing plants soon after harvesting

Short period Storage should be in stacks or bags kept in ordinary buildings or godowns after sun drying

Filling in neat & clean bags, if old then properly treated before use

Proper labeling The stacks of bags should be made on wooden

pallets. Storage place should be: Properly clean Dry Cool Sprayed with malathion fumigated