current trends in onion breeding

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Journal of New SeedsPublication details including instructions forauthors and subscription informationhttpwwwtandfonlinecomloiwjns20

Current Trends in OnionBreedingA S Sidhu a S S Bal a amp Mamta Rani aa Department of Vegetable Crops PunjabAgricultural University Ludhiana 141004 IndiaVersion of record first published 24 Sep 2008

To cite this article A S Sidhu S S Bal amp Mamta Rani (2005) Current Trends inOnion Breeding Journal of New Seeds 62-3 223-245

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Current Trends in Onion Breeding

A S SidhuS S Bal

Mamta Rani

SUMMARY Onion is an important vegetable crop worldwide and hasbeen used in various forms as food There are different types of onionavailable depending on shape size and color To a lesser extent theprocessing industry uses it in the form of dehydrated onion flakes andpowder one of the remarkable features of onion is its excellent trans-portability The normal flower in onion is perfect The flowering structureis called an umbel It is an aggregate of many small flowers Photoperiodis an important factor in bulb development Normally onion is a long dayplant Heterosis has been commercially exploited in onion as male ster-ile lines are available in this crop The male sterility was reported in thecrop long back in 1936 Honeybees are used for necessary transfer ofpollen from male parent to female parent More research is needed onfactors affecting attractiveness of onions to honeybees The paper dis-cusses in detailed information regarding research in heterosis pollina-tion control mechanisms breeding for hybrids and techniques related tohybrid seed production [Article copies available for a fee from The HaworthDocument Delivery Service 1-800-HAWORTH E-mail address ltdocdeliveryhaworthpress comgt Website lthttpwwwHaworthPresscomgt copy 2004 by TheHaworth Press Inc All rights reserved]

A S Sidhu S S Bal and Mamta Rani are affiliated with the Department of Vegeta-ble Crops Punjab Agricultural University Ludhiana 141004 India

[Haworth co-indexing entry note] ldquoCurrent Trends in Onion Breedingrdquo Sidhu A S S S Bal andMamta Rani Co-published simultaneously in Journal of New Seeds (Food Products Press an imprint of TheHaworth Press Inc) Vol 6 No 23 2004 pp 223-245 and Hybrid Vegetable Development (ed P KSingh S K Dasgupta and S K Tripathi) Food Products Press an imprint of The Haworth Press Inc 2004pp 223-245 Single or multiple copies of this article are available for a fee from The Haworth Document De-livery Service [1-800-HAWORTH 900 am - 500 pm (EST) E-mail address docdeliveryhaworthpresscom]

httpwwwhaworthpresscomwebJNScopy 2004 by The Haworth Press Inc All rights reserved

Digital Object Identifier 101300J153v06n02_12 223

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KEYWORDS Onion heterosis male sterility breeding pollinationcontrol mechanisms maintenance of inbred lines hybrid seed produc-tion

INTRODUCTION

Onion is an important vegetable crop worldwide and has been used as foodsince time immemorial It is used for flavoring or seasoning the food both atmature and immature bulb stages besides being used as salad and pickle To alesser extent it is used by the processing industry for dehydration in the formof onion flakes and powder which are in great demand in the world market Itis one of the few versatile vegetable crops that can be kept for a fairly long pe-riod and can safely withstand the hazards of rough handling including longdistance transport

India ranks first in area and second in production after China Onion isgrown in an area of 26 lakh hectares producing about 27 lakh tones of bulbsfor local consumption as well as for export purpose It is grown in all conti-nents with world production of about 25 million tones and is commerciallygrown in a little over hundred countries of the world However about three-forth of global production is accounted for by 18 countries important of whichare China India USA USSR Japan Spain Turkey Brazil Iran etc Indiarsquosshare in the world production is about 11 percent (Currah and Proctor 1990)Of the fifteen vegetable crops listed by FAO (Anon 1973) onion falls secondonly to tomato in terms of annual world production In overall cropping pat-terns onion area represents about 01 percent of gross cultivated area under allcrops in the country and about 7 percent of the total area under all vegetablecrops

Cytology The Allium cepa species are diploid with basic chromosomenumber of x = 8 (2n = 16) Occasional tetraploids have also been reported Of8 pairs of chromosomes 7 are metacentric or submetacentric and one is satel-lited subtelocentric chromosome with nucleolus organizer region Onionchromosomes are relatively large and spread easily during slide preparationfor cytogenetic studies Heterochromatic DNA is distinguishable from euchro-matic DNA by Geimsa C banding G banding Q banding and florescence Theheterochromatic segments lie near the ends of chromosomes and show lowquinacrine florescence and appear as dark bands with geimsa staining Thesatellites are also deeply stained There are morphological and cytologicalsimilarities between the species of section cepa but still strong crossing barri-ers exist between them This prevents gene flow between the two even wheresympatric distribution of two species occurs Introgression of genetic material

224 HYBRID VEGETABLE DEVELOPMENT

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from wild to cultivated species is also difficult Low success has been recordedin several interspecific hybridizations

CROP BIOLOGY

The Onion Plant Family Liliaceae (Lily) or Amaryllidaceae (Amaryllis)

Species Allium cepa

This plant is a genus of strong smelling bulbous herb either of the Lily Fam-ily or Amaryllis Family It includes more than 300 species of which about 70are cultivated some as ornaments most as vegetables Onions garlic leekchive and their relatives are all members of this family

The onion that we eat (Allium cepa) is a hardy biennial grown as an annualfrom seed or from sets (small bulbs) It is usually grown for its firm ripe bulbsbut also grown for its immature stems (shallots and green onions) These twotypes are known as ldquobulbousrdquo and ldquobunchingrdquo Onions are ldquotunicaterdquo bulbswhich mean that the scales are covered by a thin skin known as tunic Thesescales are also called ldquowrapping scalesrdquo The bulb is a modified shoot orflower bud that forms underground though close to the surface of the soil Thethick scales that protect the bud are actually swollen leaf bases The scales areanchored to a tough basal plate (the flat end of the bulb) from which the rootswill grow The layers of scales store food to nourish the bulbs when the plantrsquostop growth dies back The bulb actually contains nearly everything that theembryonic bud will need to grow and bloom including a lot of water

The sulfur is absorbed out of the soil and into the onion through its rootsWhen onion is cut into the sulfur compounds are released into the air When itreaches the saline solution that your tears are made up of it combines and be-comes a mild form of sulfuric acid This is what makes people cry Especiallysweet onions contain very small amounts of the sulfur-containing compoundsonly about 50 of the typical levels found in other varieties We taste sugar in-stead of the sulfur and they are much sweeter Ironically sugar levels in sweetonions are only slightly greater than those of some storage onions

Floral biology According to Pike (1986) flowering of onion is initiated byenvironmental factors The primary inductive factor is cool temperature Tem-perature of 40degF or below for 1 week will generally induce flower formation inbulbs or in growing plants with four or more leaves However temperatureprior to and following the 40degF week can alter flower induction Very smallseedlings do not normally respond to cool temperatures The larger the plantgenerally the more easily it can be induced to initiate flower developmentWhen the onion plant is induced to flower the shoot apex ceases to produceleaf primordia and initiates the inflorescence The inflorescence may consist

Sidhu Bal and Rani 225

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of a few to more than 2000 flowers per umbel The flower stalk (scape orseedstem) which bears the umbel consisting of spathe and the flowers is actu-ally a one-internode extension of the stem The stalk is initially a solid struc-ture but with growth it becomes hollow as it develops The number ofseedstems produced per plant depends on the number of lateral buds containedon the stem which is compact base plate on the bottom of the bulb (Figure 1)

Plants grown from seed usually produce only one seedstem if induced toflower Plants grown from bulbs may produce 6 or more seedstems since sev-eral lateral buds may be present that formed during development of the bulb Itshould be noted that it is common for plants to produce bulbs and seedstemswhen grown during winter and into the spring This is due to the fact that oneor more buds remain vegetative and produce leaves that form the bulb while alateral bud is initiated to form a seedstem The plant then has both a bulb and aseedstem present at the same time

The flowering structure is called an umbel (Figure 2) It is an aggregate ofmany small inflorescences (cymes) of 5-10 flowers each of which opens in adefinite order causing flowering to be irregular and to last for 2 or more


MAIN AXIS

ROOT

LATERAL BUDS

MODIFIED LEAFBASES MAKING THEBULB STRUCTURE

FIGURE 1 The stem of an onion is very compact and generally not seen by thecasual observer The leaf base enlarges upon bulb initiation and form the bulbUpon flower initiation seed stems form in the apex of the leaf axis and elongateup through the bulb

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FIGURE 2

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weeks If the plant produces two or more seedstems the flowering sequencemay actually occur for over a month (Figure 3)

Each individual flower is made up of six stamens three carpels united withone pistil and six perianth segments (Figure 4) The pistil contains threelocules each of which contains two ovules The flower also contains nectarieswhich secrete nectar to attract insects The stigma becomes receptive at thistime and as a result of delayed female maturity (protandry) cross-pollinationis favored After pollination the seeds develop as they are mature the cap-sules dry and split from the apex and down the center of each locule which al-lows the seeds to fall free upon maturity

The normal flower in onions is perfect but genetic and cytoplasmic sterilityvariations were discovered and reported by Jones and Emsweller (1933) in asingle-plant segregate of the cultivar Italian Red Male-sterile plants devel-oped from this original plant produced normal flowers except that the pollendid not develop into a viable stage The inheritance was determined by Jonesand Clarke (1943) to be conditioned by a single recessive nuclear gene msmsand a cytoplasmic factor where one cytoplasm is considered normal (N) andthe other sterile (S) To be made sterile the onion plant must have the geneticand cytoplasmic condition Smsms The discovery propagation and tech-niques of maintaining male sterility in the onion have provided an excellentmethod for producing hybrid seed


FIGURE 3

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The flowering stalk of onion is an apical extension of the stem but withoutnodes and internodes The growth of flower stalk ceases when umbels start toflower The length of scape (flower stalkseed stem) is controlled by geneticfactors long stalks being dominant over dwarf Spherical umbel which termi-nates the stalk may have 50 to 2000 flowers common range being 200-600Inbreds produce significantly less flowers per head than heterozygous plantsEach flower is attached to a slender pedicel Secondary umbels (those raisingfrom branches that have already flowered) have approximately 30-50 of thenumber of the flowers in the primary heads The flower stalk of onion reachesto a final length of 1-2 meters The growth of flowering stalk is stopped whenumbels start flowering

Length of the day (Photoperiod) Photoperiod is an important factor in bulbdevelopment This term describes the effect of day length on bulb formationSome onion varieties have a short day length response forming bulbs whenthe days are 12 hours or less Other varieties have a long day length responseforming bulbs when there are 15 or more hours of daylight

Onion is normally regarded as a long day plant and the bulb formation ispromoted by long-day conditions The cultivars differ greatly in day length re-quirement and there are some cultivars like ldquoCojumatlanrdquo (Mexican cultivar)where bulb formation may start under short day condition Correctly speakingit is not a short day cultivar and apparently it may appear so since the bulb for-mation may become effective under relatively shorter photoperiodic condi-tion In fact photoperiodic requirement in onion is a quantitative character andeach cultivar needs a minimum day length for bulb formation which is known


SEPALS

OVARY

STYLE

ANTHER

FIGURE 4 Each individual onion flower within the umbel is complete havingsix stamens three carpels united with one pistil and six perianth segmentsThe pistil contains three locules each of which contains two ovules

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as critical value This critical value in combination with temperature influ-ences bulb initiation The so-called short day cultivars when pass the criticalvalue limit will initiate bulb formation and development and is continued un-der long day conditions Conversely a long day cultivar will not be able to ini-tiate bulb formation unless its longer critical value of photoperiod is reachedAoba (1967) has reported that under long day and high temperature leafgrowth was inhibited and ceased completely within 25-30 days of the start oflong day treatment When short day (8 hours light) treatment was given to theplants for 30 days before the long day treatment growth was accelerated andlarge bulbs were formed Kato (1964) found that the effect produced by longphotoperiod during bulb formation was neutralized if long day treatment wasinterrupted by a period of short days and the bulb-forming phase was revertedto vegetative phase It was experimentally possible to reverse the bulb forma-tion phase even after the tops have fallen over

Interesting findings of Heath and Hollies (1965) showed that if onion plantswere kept under short day condition they continued growing for three yearswithout bulbing Kononkov et al (1969) tried some cultivars from Europe Is-rael and USA in Cuba and found that the only cultivars from the countriesapproximately of the same day length of Cuba produced bulbs Those of farnorthern region did not produce any bulb Austin (1972) showed that the re-sponse of different cultivars to day length remained in the same order relativeto each other over a wide range of photoperiodic treatments

Growth requirements Onions are usually grown on loam or silt loam soilshaving good water holding capacities Good crop rotation is a necessity Ro-tated crops may include small grains potatoes and sugar beets The fields areprepared in the fall fumigated bedded and the residue ploughed under Theyare left to mellow over winter Onions grow well in the soil with a pH pf 55 to70 though the onionrsquos sensitivity to acid soils lead them to grow best in soilwith a pH between 62 and 68

Bulbs can reproduce by means of underground offsets called bulblets(called ldquosetsrdquo) However most growers use onion seed Onions grown fromseed will mature into bulbs in about five months Seed-raised onions are mostimportant commercially because it is their ripe bulbs that can be shipped orused for storage There are approximately 9500 onion seeds per ounce An av-erage of one to three pounds are used per acre depending on the desired sizeMost onions are direct seeded though sometimes over wintered sets are trans-planted in spring Onion seeds are usually planted at a depth of 12 to 1 inchGrowers usually use precision seeding techniques placing individual seeds ata predetermined spacing within a row The result is highly uniform crop withhigh yield of the desired size

Depth of seeding has an effect on bulb shape since the onion stem plate (thebase of the onion bulb) forms at the point where the seed germinates Shallow


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planting results in flatter bulbs while the deeper seed placement results intaller and sometimes top-shaped bulbs The most common planting practice istwo rows planted per raised bed

Growers usually prefer to not have to irrigate until the onion plant hasemerged from the soil Then the fields are irrigated regularly until the plant hasmatured Soil conditioning is necessary Onion plants are shallow-rooted andplant growth is good when nitrogen is carefully applied with irrigation waterIt is important that excellent plant development is achieved before bulbingstarts The best foliage and root development occurs when the temperaturesare cool (55 to 75degF) After bulbing begins high temperature and low humid-ity continuing through out the harvest process are important Through the en-tire growing process adequate soil moisture must remain constant

Maturation and harvest A plant is considered to be mature when it stopsgrowing When this happens the grower stops irrigating The bulb will con-tinue to grow even after the water is withheld When 25-50 of the onion leaftops have fallen over the plant is ready to be lifted from the ground The liftersmove carefully through the fields so as not to create clods The plants are care-fully lifted from the ground and are left to wilt They must dry rapidly (cure)before they are topped If an onion has not cured properly it is very susceptibleto neck rot Ten or more days later when leaves are dry a mechanical oniontopper cuts the tops off the onion bulbs Clods are removed or covered with adrag so that the bulbs can drop softly to the ground Any breaks in the skin canleave the bulb susceptible to rot and other diseases Again the onions are leftto lie in the fields They will cure for at least three or more weeks before theyare lifted again and bulked for storage

HETEROSIS

Onion is one of the pioneer crops in which heterosis has been commerciallyexploited since about four decades Although India is one of the leading onionproducers not much emphasis was given to heterosis breeding in the past Oneof the main components for exploiting heterosis in onion is the availability ofmale sterility In India progress in the development of suitable male sterileand fertile inbred lines remained very slow in the past few decades Sen andSrivastava (1957) attempted to develop F1 hybrids in onion as early as in 1948using exotic male sterile lines and Indian local male stocks The exotic malesterile lines were found unsuitable in the photoperiodically different environ-ment in India Later very few workers attempted to test different hybrid com-binations for heterosis and combining ability studies using male sterile lines(Pathak et al 1987)


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Male sterility has been isolated from indigenous germplasm by severalworkers in IndiandashPatil et al (1973) in cv Niphad 2-4-1 Pathak et al (1980) incv Nasik White Globe (IIHR 20) Further studies indicated strong cytoplas-mic factor responsible for male sterility in cv Bombay White Globe (Pathak etal 1986) This male sterility has been transferred to several breeding lines bybackcross breeding method In the hybrids of 3 male sterile testers and 20 in-bred lines various economic traits have been studied Positive heterosis wasobserved in 9 hybrids over better parent for total bulb yield and it ranged from479-895 while heterosis over best parent for marketable bulb yield wasover 35 in three hybrids ie MS1 NER-1 MS1 IIHR21-1 and MS8 IIHR 52-1 (Pathak et al 1987) Popandron (1998) obtained three F1 hybridsby crossing a male-sterile line of onion with inbred lines in the S2 were studiedfor 3 years (1990-92) at Vidra Biometrical measurements of plant height leafbreadth number of leaves per plant and yield were made for both F1 hybridsand their parents Heterosis was clearly evident for plant height and yield lessfor leaf breadth and completely absent for number of leaves per plant Ac-cording to Janik et al (1999) crop uniformity is considered a desirable charac-ter in modern agriculture because product uniformity is essential in marketinguniformity in maturity permits crop scheduling and uniformity in plant struc-ture and maturation permits efficient mechanical harvest Furthermore cropuniformity is essential for maximizing yield a little understood feature ofuniformity that is expanded in this chapter Production of F1 hybrids ofseed-propagated crops is a successful breeding technique because it exploitsheterosis promotes homogeneity in allogamous species and is a way for com-mercial breeders to control their product The uniformity of hybrids has twodimensions (1) genetic homogeneityndashthe presence of identical genotypesand (2) genetic stabilityndashphenotypic uniformity (homeostasis) in differentenvironments Methods to achieve genetic homogeneity are discussed in-cluding vegetative or clonal propagation selection inbreeding and produc-tion of F1 hybrids The discussion on genetic stability includes ways inwhich to characterize stability the genetics of stability and the role of popu-lation buffering in competition and stability Further information is pre-sented on maximizing genetic progress strategies for achieving uniformityand stability in maize tomato and onion and uniformity vs stability in subsis-tence agriculture Netrapal et al (1999) conducted a study during 1994-96 forthe heterosis in line tester cross of onion (Allium cepa) 3 lines (male-sterileparents) and 23 testers (fertile male parents) thus making a total of 26 inbredparents and their 69 F1rsquos along with 6 controls quite a good number of F1rsquosshowed desirable heterosis over the top parent for all characters except a fewfor maturity and neck thickness All the characters revealed superiority of F1rsquosover the standard controls Mostly the better performing F1rsquos also expressedhigher heterosis over the better parent top parent and standard control The


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F1rsquos (102-1 106) Smsms 26-3-8-2op P 5 75 Smsms Early GranoPusa Red Smsms Bahadurgarh Local P 1 75 Smsms 31-7-60-0-p-3 and (102-1 106) Smsms 28-12-9 -8 emerged as better performing F1rsquoswhich gave 2448-5862 heterosis in yield over the top parent For neckthickness (102-1 406) Smsms 31-7-6-op-3- P 5 gave heterosis of191 over top parent The hybrids 75 Smsms Early Grano and (102 106) Smsms 26-3-8-2 P 5 gave more uniform bulbs than any other F1 orthe control For total soluble solids the hybrids (102-1 106 Smsms) SI 13showed 60 heterosis over the top parents For storage Pusa Red Smsms SI13 gave heterosis of 3142 over the top parent

Mani et al (1999) crossed 5 red-skinned open-pollinated populations asmales to 4 exotic yellow-skinned cytoplasmic male sterile inbred lines The re-sulting 20 F1 hybrids and their 9 parents were evaluated at 2 locations(Hawalbagh and Bhowali) in the Uttar Pradesh hills The results indicated pos-itive and significant heterosis over the better parent for bulb yield in the crossinbred 13 L 43 In this study the F1 between Inbred 13 L 43 was used as abase material advanced to the F2 and subjected to 3 cycles of mass selectionfor bulb yield skin colour shape and size An improved high-yielding onionstrain was thus developed and designated VL Piaz 3 It was released in 1993for the hills of Uttar Pradesh In trials at Hawalbagh it produced a 206-474higher yield over recommended controls VL Piaz 3 combines a fairly goodlevel of field tolerance of purple blotch and thrips and a reduced tendency tobolting It produces medium-sized flat-globular red bulbs EL-Sayed et al(1999) evaluated the parents and F1 hybrids from a half-diallel cross of onionfor earliness (days from transplanting to harvest date) bulb ratio (neck diame-terbulb diameter) number of leaves per plant bulb height and entire rings intrials conducted at the Onion Research Centre at Cairo Based on the resultsobtained information is derived on genetic variance heterosis and heritabilityHighly significant additive and non-additive gene effects were involved in theinheritance of all characters The magnitude of mean square of the specificcombining ability appeared small in comparison with that of the general com-bining ability indicating that additive type genetic variance is more importantin control of these characters A pronounced hybrid vigor was detected formost of the studied traits indicating that non-additive gene effects also have asignificant role in the inheritance of these characters

POLLINATION CONTROL MECHANISMS

Pollination control Pollination control in cross-pollinating species such asin onion is extremely difficult considering each umbel has several hundredtiny individual flowers Therefore it is important to understand onion flower-


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ing habits and the inheritance of as many characters as possible to be efficientin breeding of the crop

In case of normal open pollinated cultivar selfing can be done only on alimited basis because inbreeding depression begins showing in the secondgeneration To make initial cross between two selections the breeder has twochoices One is to hand emasculate stamens from one line which is extremelydifficult The fact that the flowers open on an umbel for 2 or more weeks addsto the problem of making the cross The second choice is to make a fertile fertile cross where two selections are caged together and then pollinated byhand or with insects such as common houseflies or bees This method can effi-ciently be utilized if two selections are difficult enough so that the F1 can bedifferentiated from two parents in the bulb stage If they are different in that re-spect seed should be saved separately from two plants and planted in separateprogeny rows The hybrid bulbs can then be identified and distinguished frombulbs resulting from selfs of the two original parents that were caged togetherThe F1 bulbs are harvested and then caged together to produce F2 progeny orthey can be used in back cross program

Pollination requirements Pollination in onion flowers occurs when pollenis transferred from the dehiscing anthers of one floret to a receptive stigma ofanother floret Effective transfer of pollen between florets on an umbel or anindividual plant can transpire through the action of an outside agent butself-pollinating within the florets is impossible Cross-fertilization betweenplants is common and even obligatory in the fertilization of male sterile onionsused in hybrid seed production Ven der Meer and Van Bennekom (1968) re-ported only 9 self-fertilization and later (1969) they concluded that seedset was less at lower temperature than higher ones

The discovery of male sterility in onions (Jones and Emsweller 1936) madethe production of hybrid onions possible under commercial conditions andmost of the onion seed produced now is hybrid seed The procedure for utiliza-tion of male sterility in onions which should be applicable to any crop plant inwhich male sterility is inherited in similar way was shown in detail by Jonesand Clarke (1943)

In the production of the hybrid seed a male sterile row of a desired line tosupply pollens to 3 to 10 rows of male sterile line (Franklin 1958) from whichthe hybrid seed should be obtained Naturally the greatest volume of hybridseed produced is desired therefore the male fertile or ldquobullrdquo rows are kept at aminimum distance provided pollen is distributed sufficiently to set seedEricksen and Gabelman (1956) showed that pollen dispersal from appoint waslogarithmic with pollination at 7 feet from a source only one-half that occur-ring at 1 foot To secure maximum seed set the grower encourages pollen dis-persal to maximum degree possible (Jones and Mann 1964)


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MacGillivray (1948) showed that highest seed production occurred at Da-vis California when plants received more than sufficient irrigation LikewiseHowthorn (1951) obtained considerably higher seed yield with higher soilmoisture Nye (1970) reported that pollinator response to ldquowetrdquo treatmentswas scarcely apparent but use of nitrogen and phosphorus fertilizers causeddecreased flower attractiveness

Pollinators Wind is not a factor in onion pollination (Erickson and Gebelman1956) Insects are the primary vectors When onion breeder wants to get sewedfrom a specific plant they enclose the flower umbel within a bag or cage andintroduce flies to transfer the pollen or if cross-pollination is desired theumbels of the two lines are enclosed (Jones and Emsweller 1933) In largecage breeding work or pollination studies honeybees are the primary agentsused (Shrick et al 1945 Moffett 1965 Walsh 1965 Bohart et al 1970)

In commercial production of seed the provision of and adequate number offlies is impractical so the industry depends upon honeybees as the primaryagent Bohart et al (1970) reported 267 species of insect visitors on onionflowers the most important of which are honeybees and drone flies Of theseonly the honeybees can be manipulated and used in large-scale onion seed pro-duction Honeybees are effective pollinators of open pollinated onions be-cause both pollen and nectar are available on all umbels In hybrid seedproduction where male sterile plants are used only the nectar collectors movefreely pollen sterile to pollen fertile plants making the necessary transfer ofpollen from male parent to female parent Honeybees then become less idealpollinators of male sterile onion Pollen collecting bees confine much of theiractivity to the pollen producing rows without adequately visiting and cross-pollinating the male sterile rows (Lederhouse et al 1972) A strictly nectarcollecting type of bee would be ideal because it would cross visit and effec-tively pollinate male sterile flowers In the absence of this perfect type of beethe grower can only try to compensate by having more honeybees present inthe field Then lack of intense attractiveness of onions to bees may cause thebees to neglect the crop particularly if another highly attractive crop is inflower The growerrsquos only attractiveness is to make crop as attractive as possi-ble with best cultural practices and to use a heavy population of bees Eventhen the seed yielding potential of crop may be never attained (Franklin1970)

More research is needed on factors that affect attractiveness of onions tohoneybees (Sanduleac 1969 Singh and Dharamwal 1970) Franklin (1970)noted that more placement of honeybee colonies in the onion field does notguarantee that the bees will work on onions Although Nye et al (1971) re-ported an average of 100 bees per 100 feet of male fertile rows and a maximumof 40 per 100 feet on male sterile rows the number of honeybee visitorsneeded per onion plant umbel or linear feet of row has not been determined


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Stuart and Griffin (1946) used different rates and times of application of ni-trogen on onions in greenhouse and used honeybees to provide pollinationTheir best production was 32 seed stalks per plant and 75 grams of seed perplant with a high nitrogen application from August 15 to January 1 low nitro-gen during January-February (blooming) then high nitrogen until maturity

Pollination recommendations and practices As early as 1936 Shaw andBourne indicated that onion seed growers might find it useful to provide them-selves with a supply of bees They did not go into details as to number of colo-nies strength or location Hamilton (1946) stated that a grower producedmuch more onion seed than he had in past after he rented 8 colonies of beesSanduleac (1961) stated that bees increase production of onion and leek seedin Romania 8 to 10 times and he recommended about 2 colonies per acre LeBaron (1962) stated that use of bees for pollination of onions in the ImperialValley of California was a ldquomustrdquo and that two colonies per acre had givengood results

There have been no clear-cut guidelines on the use of bees for maximumonion seed production and many beliefs based on limited observation havearisen These include the size of colony cluster its relative stage of develop-ment and previous usage The grower has learnt through experience that theuse of honeybees is essential and is frequently frustrated by the erratic activityof the bees They have generally adopted the practice of renting 5 to 10 colo-nies of bees per acre and having them placed in or adjacent to their seed fieldsat flowering time One suggestion has been to have about 2 colonies per acredelivered when flowering is well started then an additional two per acre at 3 to4-day interval to take advantage of native bee behavior and maintain somelevel of nectar foraging activity throughout the blooming stage

Much information is needed on the factors that influence the activity ofbees on onion flowers because as Franklin (1970) pointed out the mere place-ment of colonies in the field does not guarantee that the bees will work on on-ions Continuous nectar foraging activity is the essential factor in hybrid onionfields especially during the peak period of flowering

HYBRID SEED PRODUCTION

The hybrid onion program originated in 1925 with the discovery byDr H A Jones of a bulb (15-53) in material of ldquoItalian Redrdquo Dr Henery AJones a former Professor of Vegetable Crops at University of California Da-vis and Research Horticulturist with US department of Agriculture and lateron with the Desert Seed Company El Centro California is truly ldquoMr Onionrdquohaving spent a lifetime of productive research with onion as quoted byWhitaker (1979) Bulb 13-53 was probably the single most important onion


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bulb ever grown because of its impact on onion breeding and breeding pro-gram in general It was a great pleasure that 13-53 could be propagated vegeta-tively as it produced bulbils in the umbels placed in the seeds Also malesterility was found to be stable under wide range of environmental conditionsThe bulbils were saved and replanted to generate new plants which werecrossed with other onion cultivars and the progenies were grown to understandthe inheritance of the male sterile character

The results proved that the male sterility was determined by an interactionbetween a nuclear gene and a cytoplasmic factor The cytoplasmic factor wasdesignated N for normal fertile cytoplasm and S for the sterile cytoplasm Thenuclear genetic condition was designated as Ms- for the normal fertile cyto-plasm and msms for the sterile condition

Male sterility can be maintained only when S msms is crossed as femaleparent with N msms as the pollen parent The line N msms is also known asmaintainer or B line Havey (1999) reported that the primary source (S cyto-plasm) of cytoplasmic-genic male sterility (CMS) used to produce hybrid on-ion (Allium cepa L) seed traces back to a single plant identified in 1925 inDavis California Many open pollinated populations also possess this cyto-plasm creating an undesirable state of cytoplasmic uniformity Transfer ofcytoplasms from related species into cultivated populations may produce newsources of CMS In an attempt to diversify the cytoplasm conditioning malesterility the cytoplasm of Allium galanthum Kar et Kir was backcrossed forseven generations to bulb-onion populations The flowers of galanthum-cyto-plasmic populations possess upwardly curved perianth and filaments with noanthers making identification of male-sterile plants easier than for either S- orT-cytoplasmic male-sterile onion plants Mean seed yield per bulb of thegalanthum-cytoplasmic populations was measured in cages using blue-bottleflies (Calliphora eythrocephala Meig) as pollinators and was not signifi-cantly different from one of the two S-cytoplasmic male-sterile F1 lines aT-cytoplasmic male-sterile inbred line or N-cytoplasmic male-fertile linesMale-sterile lines possessing either the S galanthum cytoplasm were eachcrossed with populations known to be homozygous dominant and recessive atthe nuclear locus conditioning male-fertility restoration of S cytoplasm andprogenies were scored for male-fertility restoration Nuclear restorers of malefertility for S cytoplasm did not condition male fertility for the galanthum-cy-toplasmic populations It is intended that these galanthum-cytoplasmic onionpopulations be used as an alternative male-sterile cytoplasm for the diversifi-cation of hybrid onion seed production

Breeding of hybrids The development of F1 in onion requires the develop-ment of a male-sterile line (A line) an inbred maintainer for a line (B line) anda pollinator male line (C line) These lines have the following genetic constitu-tion


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A line = S msms

B line = N msms

C line = N MsMs

The procedure of developing A and B lines by backcrossing has been outlined as follows

Male-sterile line (A) Male-fertile line No 2 (B)

S msms N msms

F1 S msms (50 No 2) N msms

BC1 S msms (75 No 2) N msms





It may be possible to find male-sterile individuals within local adopted pop-ulations and if so appropriate pairs of male-sterilemaintainer lines can be devel-oped from these Alternatively the breeder may start with known male-sterilelines usually from unadapted cultivars made available to him by other onionbreeders or genetic conservationists These are converted to male sterile linesby crossing and back crossing with selected maintainer lines Disregarding theoriginal source of male sterile the objective is same ie the production ofisogenic pairs of male-sterilemaintainer lines of agronomics value The initialtest crosses are grown to flowering and only those test crosses are used in fur-ther back crossing which are found to be male sterile After 4-5 back crossesthe lines A (S msms) and B (N msms) become almost genetically identical ex-cept for sterility in line A and the other lines remain fertile A line is main-tained by crossing with B line and B line is maintained through selfing

Development of pollinator line ie C line (N MsMs) proceeds concur-rently with that of male-sterile lines Usually open pollinated selectionpromis-ing crosses are used as base population for this purpose Generally 3 generationsof selfing with field selection are carried out

A schematic plan for breeding improved onion hybrids as outlined by Pike(1986) is given as


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Year Procedure

1 Grow and select 100 bulbs store and plant also grow supply ofmale-sterile bulbs for use in test crosses

2 Self selected bulbs and at the same time test cross with knownsterile

3 Grow out bulbs from self and F1 testcrosses select discard poorprogeny rows and their F1 pair store

4 Plant bulbs for seed production observe sterility characters in F1lines if 100 sterile self selections and make back cross to F1discard pairs with fertile F1 lines

5 Grow out A and B lines as pairs continue to select in B line sidesave best bulbs from a line for next backcross

6 Self B line of selected progenies and make backcross to sterileside of pair

7 Grow bulbs and make final selection on the basis of B line side

8 Mass B line using 10-20 bulbs in cage while making thebackcross to the sterile side of pair

9-12 At this point begin seed to seed and continue through the fifthbackcross using the same procedure as in the 8th year several Aand B lines should have been developed begin making hybridcombinations for testing

Maintenance and multiplication of lines A B and C The first increase ofseeds of the lines A is done in insect proof cages followed by an increase in theopen but not more than twice to obtain high degree of purity in stocks seeds ofthe parental lines The seeds of the lines A and B can be increased in same cagewhile the line C must be grown separately in another cage A nylon or wire netcage of 20 20 or 24 24 mesh measuring 6 m 3 m 2 m with a smalldoor at one corner for entrance and exit is suitable for this purpose This size ofcage can accommodate 4 rows of bulbs spaced 60 cm apart to produce about1-25 Kg of seeds In the cage bulbs of line A and B should be planted in alter-nate rows with equal number of bulbs of each Before flowering the cage is putover the plants The umbels should not touch the cage as it would allow thestigma to protrude and get contaminated with foreign pollen About 3 days be-fore the commencement of flowering a bee hive of medium size colony with a


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queen is placed inside the cage Ten percent sugar is used as feeding mediumIt is necessary to rogue out pollen bearing plants from A line and pollen sterileplants if any from B line every morning before the dehiscence of anthers TheC line can be multiplied in the same way in a separate cage

For planting areas of commercial seed crop it will be necessary to increasethe seed of A B and C lines in open in isolation with an isolation distance of32 km The plot size is about 04 ha (Swarup 1991)

Production of hybrid seed The hybrid seed is produced in the open isolatedfield The bulbs of A and C lines are planted alternatively in a ratio of 4 rows ofA line to 1 row of C line (Swarup 1991) The conventional ratio is 82 How-ever a higher planting ratio gives better seed yield In UK 91 ratio has beenfound good The flowering of A and C lines must synchronize If needed syn-chrony can be achieved by

1 Adjustment of storage temperature (warmer storage temperature withinthe range of 0-12degC causes earlier flowering) and

2 Adjustment of planting dates (early planting causes earlier flowering)

In large fields 3-4 beehives040 ha are placed to ensure large population ofhoneybees for cross-pollination Daily rouging of pollen shedding plants andother off-types in A line in the morning before dehiscence of anthers is essen-tial

Frequently the seed from the pollinator row is discarded The male plantsare destroyed before the female is harvested to avoid contamination of the fe-male seed with accidentally harvested seed from the male parent If both themale and female parents are to be harvested the male should be harvested beforethe female and earlier than the optimal harvest time so that the more valuablehybrid seed can be harvested at its optimal time and free from contaminationby accidentally harvested seed from the male

Hybrid seed production often produces lower seed yields per unit of landoccupied by the female line than the yields of the open pollinated cultivarsThe process of stabilizing a male sterile line can reduce its vigor and fruitful-ness due to inbreeding depression Studies have attributed this due to

1 Reduced number and size of umbels2 Reduced period of receptivity in individual flowers and3 Ovule abortion

This tendency may be overcome by using single cross females without los-ing too much uniformity in the hybrid (Peters 1990)

Use of molecular tools in onion geneticsimprovement Use of moleculartools as an indirect assay of desired traits can substantially accelerate a breed-


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ing program This would be a major benefit for a crop such as onion which re-quired 2 years per generation The use of molecular techniques for onions isrecent but developing very rapidly Onion is a diploid species with 14 chro-mosomes per cell its nuclear DNA content per cell (referred to as genomesize) is very high DNA isolation is relatively easy producing copious amountsof high quality DNA The large size of onion genome suggested the need foruse the PCR-based technique AFLP rather than RFLP or the simpler PCR-based method of RADPs AFLP works well in onion without any modificationin protocol yielding clean genetic fingerprints

There are protocols within domesticated onions (A cepa) for the produc-tion of haploid then doubled haploids though ovary culture The accelerationin inbred development this approach allows is very attractive in a biennialcrop such as onion We are interested in adapting it to allow production ofdoubled haploids with randomly introgressed portion of related wild genomesstarting A roylei The resulting lines would be extremely useful in genomestudies detection and transfer of QTL or single major genes affecting impor-tant traits such as the ability and timing of bulbing

SEED PRODUCTION

Onion seed is usually produced in temperate and subtropical countries Inregions where high temperature prevails almost throughout the year only theearly bolting type of onion requiring relatively low temperature exposure canproduce seed Onion is a biennial crop for the purpose of seed production Inone season bulbs are produced from the seed and in second season bulbs arereplanted to produce seed Onion seed are poor in keeping quality and lose via-bility within a year Therefore it is essential to produce seed freshly and usethe same for bulb production

It is highly cross-pollinated crop which is facilitated by protandrous natureof flowers Its flowers are pollinated by honeybees Two methods are em-ployed in the production of the onion seed The one used most commonly isthe bud to seed method which involves first producing bulbs as for the marketand then planting them for seed production While a smaller number of seed isproduced by seed to seed method generally medium sized bulbs are selectedfor planting seeds The bigger the bulb size the higher is the yield Howeververy high sized bulbs if used will need a very high seed rate A bulb size of 25to 30 cm diameter may need 1500 kg to plant a hectare and may yield about8850 kg of seed Large sized bulbs of 3 to 4 cm diameter will need three timesmore seed bulb and may yield 1000 kg of seed per hectare Bulbs are plantedby first fortnight of October The spacing depends on the size of the bulb A


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closer spacing of 30 cm within row gives higher yields of seed than whenbulbs are planted at 45 cm for variety ldquoPusa Redrdquo

There are some varieties which do not store well sometimes someone wantsto get seed within the same year In such cases the seed to seed method is prac-ticed The seeds are sown in August and the seedlings are planted in Septem-ber Most of the bulbs give flowering stalks for seeds

In India seed to seed method is not popular Sometimes bolters do appearin the bulb crop of onion and the seeds produced from these direct bolters areconsidered unsuitable for raising the crop

Advantages of this method are high seed yield production of seed in poorkeeping cultivars within storage and less seed cost production by eliminatingexpenses on harvesting and replanting bulbs

The isolation of onion seed fields should be planned well in advance Thegreater the distance between the onion fields less will be the extent of cross-ing Other factors such as the direction of wind and weather conditions at pol-lination time influence the extent of crossing Since it is a cross-pollinatedcrop two cultivars may be kept at about 100 m apart to produce pure seed(Anon 1971)

The maturity of seed ready for harvest is indicated when fruits open and ex-pose the black seed Harvesting the seed at proper maturity is essential Onlyfully ripe seed should be harvested All the umbels do not mature at the sametime A field is considered ready for harvesting when about 10 of the headshave black seeds exposed It is desirable to harvest seed at intervals The seedheads are cut with 10-15 cm of stem attached

An average seed yield of 8-10 quintals can be expected from a hectareHigher yield up to 15 quintals are also obtained For nucleus and foundationseed production the bulb to seed method should be followed because it pro-vides opportunity for proper selection and rouging However seed to seedmethod will produce higher seed yield

CONCLUSIONS

Onion (Allium cepa) is one of the most important crop among various Al-liums grown in India and belong to family Amaryllidaceae There has been asteady increase in area and production of onion in the last decade Onion ac-counted for about 75 of total foreign exchange earning among fresh vegeta-bles Bulb and flowering of onion is initiated by environmental factors liketemperature and photoperiod The flower structure is called an umbel Thenormal flower in onion is perfect but genetic and cytoplasmic sterility varia-tions were discovered Onion is one of the pioneer crops in which heterosiswas commercially exploited since about four decades Although India is one


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of the leading onion producer not much emphasis was given to the heterosisbreeding in the past One of the main component for exploiting heterosis in on-ion is the availability of male sterility Pollination control in onion is ex-tremely difficult considering each umbel has several hundred tiny individualflowers Therefore it is important to understand onion flowering habits andthe inheritance of characters to be efficient in breeding of the crop Honeybeesare the primary agent used for pollination More research is needed on factorsthat affect attractiveness of onion to honeybees The development of F1 hy-brids in onion requires the development of a male sterile line (A line) an inbredmaintainer for a line (B line) and a pollinator line (C line) Hybrid seed is pro-duced in the open isolated field Although reasonable progress has been madeso far in the onion and research many important problems still have to be tack-led Rapid progress could be achieved through the use of simple in vitro andrapid multiplication methods

REFERENCES

Anonymous (1973) FAO Production Year BookAnonymous (1971) Indian Minimum Seed Certification Standards Central Seed

Committee Min Food Agric Comm Dev Co New DelhiAoba T (1967) Effect of different temperatures on seed J Jap Soc Hort Sci 36

333-338Austin RB (1972) Bulb formation in onions as affected by photoperiod and spectral

quality of light J Hort Sci 47 492-504Bohart GE Nye WP and Hawthorn LR (1970) Onion production as affected by

different levels of pollinator activity Agr Expt Sta Bul pp 60 482Currah L and Proctor FJ (1990) Onions in tropical regions Natural Resource Insti-

tute Bulletin No 35 pp 35 NRI UKEl-Sayed AM Atia AAM El-Hak SHG Azab AM and Mohamed HY

(1999) Studies on heterosis gene action and combining ability of some traits in on-ion (Allium cepa L) Egyptian J Hort 26 85-95

Ericson HT and Gabelman WH (1956) The effect of distance and direction oncross pollination in onions Amer Soc Hort Proc 68 351-357

Franklin DF (1958) Effect of hybrid seed production of using different ratios of malesterile and pollen rows Amer Soc Hort Proc 71 435- 439

Franklin DF (1970) Problems in the production of vegetable seeds In the Indispens-able Pollinators Ark Agr Ext Serv Misc Pub 127 pp 112-140

Hamilton RP (1946) Onions need bees Gleanings Bee Cult 74 23Havey MJ (1999) Seed yield floral morphology and lack of male-fertility restora-

tion of male-sterile onion (Allium cepa) populations possessing the cytoplasm ofAllium galanthum J Amer Soc Hort Sci 124 626-629

Hawthorn LR (1951) Studies on soil moisture and spacing for seed crops of carrotsand onions US Dept Agr Cir pp 26 892


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Heath OVS and Hollies MA (1965) Studies in the physiology of the onion plant JExpt Bot 16 128-144

Janik J Coors JG and Pandey S (1999) Exploitation of heterosis Uniformity andstability The genetics and exploitation of heterosis in crops Proceedings of an in-ternational symposium CIMMYT Mexico 17-22 August pp 319-333

Jones HA and Emsweller SL (1936) A male sterile onion Amer Soc Hort SciProc 34 582- 585

Jones HA and Emsweller SL (1933) Methods of breeding onions Hilgaria 7625-642

Jones DF and Clarke AI (1943) Inheritance of male sterility in onion and the pro-duction of hybrid seed Amer Soc Hort Sci Proc 43189-193

Jones HA and Mann LK (1964) Onions and Their Allies Leonard Hill Book CoLondon p 286

Kato T (1964) Physiological studies on bulbing and dormancy of onion plant III Ef-fects of external factors on the bulb formation and development J Jap Soc HortSci 33 53-61

Kononkov PF Ustimenko GW and Perez AP (1969) Beitr Trop Subtrop LandwTrop Vet Med 183-192

Le Baron FC (1962) Onion seed sample costs and production Calif Agr Ext SerCost Data Sheet 22 Leaflet

Lederhouse RC Caron DM and Morse RA (1972) Onion pollination in NewYork New Yorkrsquos Food and Life Sci 1 8-9

Mac Gillivray JH (1948) Effect of irrigation on the yield of onion seed Amer SocHort Sci Proc 51 423-427

Mani VP Chauhan VS Joshi HC and Tandon JP (1999) Exploiting gene ef-fects for improving bulb yield in onion Indian J Genet and Pl Breed 59 511-514

Moffett JO (1965) Pollinating experimental onion varieties Amer Bee J 105 378Netrapal and Singh N (1999) Heterosis for yield and storage parameters in onion

(Allium cepa) Indian J Agric Sci 69 826-829Nye WP (1970) Pollination of onion seed affected by environmental stresses In the

indispensable Pollinators Report of the ninth pollination conference Hot SpringsArk Oct 12-15 1970 Arkansas Agricultural Extension Service MP 127 141-144

Nye WP Wailer GD and Waters ND (1971) Factors affecting pollination of on-ions in Idaho during 1969 Amer Soc Hort Sci Proc 96 330-332

Pathak CS Aghora TS Singh DP and Deshpande AA (1987) Exploitation ofheterosis in onion by using indigenous source of male sterility National symposiumon heterosis exploitation Accomplishment and Prospects Marathwada AgricultureUniversity Parbhani India Abstr 53

Pathak CS Singh DP and Deshpande AA (1980) Annual Report of Indian Insti-tute of Horticultural Research 34-36

Pathak CS Singh DP and Deshpande AA and Sreedhar TS (1986) Sources ofresistance to purple blotch in onion Veg Sci 31 300- 303

Pathak CS Singh DP and Deshpande AA (1987) A new type of cytoplasmicmale sterility in onion First All India Conference of Cytology and GeneticsBangalore University India 1987 Abstr 46


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Patil JA Jadhav AS and Rane MS (1973) Male sterility in Maharashtra onionRes J Mahatma Phule Agric Univ 4 29-31

Peters R (1990) Seed production in onions and some other Allium species In HDRabinowitch and JL Brewster (Eds) Onions and Allied Crops Vol 1 BotanyPhysiology and Genetics CRC Press Inc Boca Raton Florida 161-176

Pike LM (1986) Onion Breeding In MJ Bassett (ed) Breeding Vegetable CropsAVI Pub Co Inc Westport Connecticut 357-394

Propandron N (1998) Revealing the heterosis phenomenon in some F1 onion hybridsobtained at the Institutul de Cercetari pentru Legumicultura si Floriculture VidraAnale-Institutulndashde- Cercetari -pentru ndashLegumicultura- si- Floriculture- Vidra1545-50

Sanduleac E (1961) The pollination of vegetable seed plants Apicultura 14 25-26Sen B and Srivastava SN (1957) Utilization of cytoplasmic male sterility in pro-

duction of hybrid onion seeds Proc 44th Indian Congr Part 2 225Shaw FR and Bourne AI (1936) Insects pollinating onions Amer Bee J 76

401-402Shrick FH Douglass JR and Shull WE (1945) Experiments for control of the

thrips initiated Idaho Agr Expt Sta Bul 35 264Singh JP and Dharamwal SS (1970) The role of honeybees in seed setting of onion

at Pantnagar District Nainital UP India Indian Bee J 32 23-26Stuart NW and Griffin DM (1946) The influence of nitrogen nutrition on onion

seed production Amer Soc Hort Sci Proc 48 398-402Swarup V (1991) Breeding Procedures for Cross Pollinated Vegetable Crops ICAR

New Delhi India 118Vander Meer QP and Van Bennekom JL (1968) Research in pollen distribution in

onion seed fields Euphytica 17 216-219Walsh RS (1965) Pollination of onion plants by honeybees New Zeal Beekeeper

27 18-20Whitaker TW (1979) The breeding of vegetable crops Highlights of the past sev-

enty five years Hort Sci 14 359-363


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Current Trends in Onion Breeding

A S SidhuS S Bal

Mamta Rani

SUMMARY Onion is an important vegetable crop worldwide and hasbeen used in various forms as food There are different types of onionavailable depending on shape size and color To a lesser extent theprocessing industry uses it in the form of dehydrated onion flakes andpowder one of the remarkable features of onion is its excellent trans-portability The normal flower in onion is perfect The flowering structureis called an umbel It is an aggregate of many small flowers Photoperiodis an important factor in bulb development Normally onion is a long dayplant Heterosis has been commercially exploited in onion as male ster-ile lines are available in this crop The male sterility was reported in thecrop long back in 1936 Honeybees are used for necessary transfer ofpollen from male parent to female parent More research is needed onfactors affecting attractiveness of onions to honeybees The paper dis-cusses in detailed information regarding research in heterosis pollina-tion control mechanisms breeding for hybrids and techniques related tohybrid seed production [Article copies available for a fee from The HaworthDocument Delivery Service 1-800-HAWORTH E-mail address ltdocdeliveryhaworthpress comgt Website lthttpwwwHaworthPresscomgt copy 2004 by TheHaworth Press Inc All rights reserved]

A S Sidhu S S Bal and Mamta Rani are affiliated with the Department of Vegeta-ble Crops Punjab Agricultural University Ludhiana 141004 India

[Haworth co-indexing entry note] ldquoCurrent Trends in Onion Breedingrdquo Sidhu A S S S Bal andMamta Rani Co-published simultaneously in Journal of New Seeds (Food Products Press an imprint of TheHaworth Press Inc) Vol 6 No 23 2004 pp 223-245 and Hybrid Vegetable Development (ed P KSingh S K Dasgupta and S K Tripathi) Food Products Press an imprint of The Haworth Press Inc 2004pp 223-245 Single or multiple copies of this article are available for a fee from The Haworth Document De-livery Service [1-800-HAWORTH 900 am - 500 pm (EST) E-mail address docdeliveryhaworthpresscom]

httpwwwhaworthpresscomwebJNScopy 2004 by The Haworth Press Inc All rights reserved

Digital Object Identifier 101300J153v06n02_12 223

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INTRODUCTION





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CROP BIOLOGY


Species Allium cepa






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MAIN AXIS

ROOT

LATERAL BUDS



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FIGURE 2

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FIGURE 3

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SEPALS

OVARY

STYLE

ANTHER


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HETEROSIS



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A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











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Year Procedure












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] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


INTRODUCTION





Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


CROP BIOLOGY


Species Allium cepa






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





MAIN AXIS

ROOT

LATERAL BUDS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


FIGURE 2

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





FIGURE 3

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





SEPALS

OVARY

STYLE

ANTHER


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


CROP BIOLOGY


Species Allium cepa






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





MAIN AXIS

ROOT

LATERAL BUDS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


FIGURE 2

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





FIGURE 3

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





SEPALS

OVARY

STYLE

ANTHER


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





MAIN AXIS

ROOT

LATERAL BUDS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


FIGURE 2

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





FIGURE 3

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





SEPALS

OVARY

STYLE

ANTHER


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


FIGURE 2

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





FIGURE 3

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





SEPALS

OVARY

STYLE

ANTHER


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





FIGURE 3

Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





SEPALS

OVARY

STYLE

ANTHER


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3





SEPALS

OVARY

STYLE

ANTHER


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3




HETEROSIS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3







Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

A line = S msms

B line = N msms

C line = N MsMs



S msms N msms











Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

Year Procedure












Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3













Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3



SEED PRODUCTION




Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3








CONCLUSIONS



Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3


REFERENCES















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3






















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3
















Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

10

05 1

3 M

arch

201

3

current trends in onion breeding

Documents