Vegetable Seed Production Principles PDF

**Principles of vegetable seed production** **Genetic Principles** Important to know which vegetable crops are self, often and cross pollinated for growing vegetable seed production. **Highly cross pollinated vegetables** 1. Wind pollinated - Amaranthus, beet leaf. Spinach, garden beet, sugar...

**Principles of vegetable seed production** **Genetic Principles** Important to know which vegetable crops are self, often and cross pollinated for growing vegetable seed production. **Highly cross pollinated vegetables** 1. Wind pollinated - Amaranthus, beet leaf. Spinach, garden beet, sugar beet 2. Insect pollinated - All cucurbits, colecrops, radish, turnip, carrot, onion. **Often cross pollinated vegetables** Lima bean, brinjal, bhendi, chilli, sweet pepper **Highly self -- pollinated vegetables** Tomato, cluster bean, French bean, cowpea, dolichos bean, garden pea, lettuce, fenugreek **Autogamy** is the kind of self pollination in which pollens are transferred from the anther to the stigma of the same flower.  **Geitonogamy** is the kind of self pollination in which pollens are transferred from the anther of one flower to the stigma of another flower on the same plant. **Conditions ensures self pollination** i. **Cleistogamy**: is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-fertilization that occurs within a permanently closed flower. Eg. Peanuts, peas, and pansy ii. **Chasmogamous:**  flowers are the type of the flower which will open only after the "self pollination" has occurred in it. The flowers are the one which do not open at all. eg. Oxalis ,viola , peas, beans, hibiscus, commelina flowers **Allogamy** -- fertilization of a flower by transfer of pollen grains from flower of one plant to stigma of another plant. **Conditions ensures cross pollination** 1. **Dicliny** : Unisexuality flowers are either staminate or pistillate i\. **Monoecy** : Staminate and pistillate flowers occur in the same plant (i.e.) either in the same inflorescence (eg) castor, mango, banana, coconut (or) in separate inflorescence (eg) Babycorn, cucurbits, grapes, cassava. 2. **Dichogamy**: Stamens and pistils of hermaphrodite flowers mature and different times i. **Protogyny** -- Pistil mature first (eg) Cucumber, chilli, bhendi, sapota, ii. **Protandry** : Stamens mature first (eg) sunflower, onion iii. **Self incompatibility** : Failure of pollen from a flower to fertilze the same flower or other flowers on the same plant (eg) Brassica sp., Radish **Male sterility** : Absence of functional pollen grains in hermaphrodite flowers. **Deterioration of Varieties** Genetic purity (trueness to type) of a variety can deteriorate due to several factors during production cycles. The best means to insure genetic purity therefore, would be to overcome to the greatest possible extent the various factors responsible for genetic deterioration. The important factors of apparent and real deterioration of varieties as listed by **Kadam (1942)** are as follows: 1\. Developmental variations 2\. Mechanical mixtures 3\. Mutations 4\. Natural crossing 5\. Minor genetic variations 6\. Selective influence of diseases 7\. The technique of the plant breeder Of these, mechanical mixtures, natural crossing and selective influence of diseases are perhaps the most important reasons for genetic deterioration of varieties during seed production followed by raising the seed crops in areas outside their adaptation which may cause developmental variations and genetic shifts in varieties. ***1. Developmental variations.*** When the seed crops are grown in difficult environment, under different soil and fertility conditions, or different climatic conditions, or under different photoperiods, or at different elevations for several consecutive generations, the developmental variations may arise sometimes as differential growth response. To minimize the opportunity for such shifts to occur in varieties it is advisable to grow them in their areas of adaptation and growing seasons. ***2. Mechanical mixtures.*** This is the most important source of variety deterioration during seed production. Mechanical mixtures may often take place at the time of sowing, if more than one variety is sown with same seed drill; through volunteer plants of the same crop in the seed field; or through different varieties grown in adjacent fields. Two varieties growing alongside each other in the field are often mixed somewhat during harvesting and threshing operations. Often the seed produce of all the varieties are kept on same threshing floor, resulting in considerable varietal mixtures. Secondly combining or threshing equipment is often contaminated with seeds of other varieties in augers, elevators, etc. Further, the gunny bags, seed bins, elevators, etc. are also quite often contaminated with seeds of other varieties. To avoid this sort of mechanical contamination it would be necessary to rogue the seed fields, and practice the utmost care during seed production, harvesting, threshing and further handling. ***3. Mutations.*** This is not a serious factor of varietal deterioration. In the majority of the cases it is difficult to identify or detect minor mutations. The mutants such as fatuoids in oats, 'rabbit ear' in peas should however, be removed by roguing from seed plots to purify the seeds. In the case of vegetative propagated crops, periodic increase of true to type stock would eliminate the deteriorating effects of mutations. ***4. Natural crossing.*** In sexually propagated crops, natural crossing is another most important source of varietal deterioration due to introgression to genes from unrelated stocks which can only be solved by prevention. The extent of varietal contamination, however, depends upon the amount of natural cross-fertilization. The deterioration in varieties due to natural crossing occurs due to the following three reasons: 1\. Natural crossing with undesirable types. 2\. Natural crossing with diseased plants. 3\. Natural crossing with off-type plants. In predominantly self-fertilized crops, natural crossing, therefore, is not a serious source of contamination and variety. Deterioration unless the variety is male sterile and is grown in close proximity to other varieties. On the other hand, natural crossing is the major source of genetic contamination and variety deterioration in cross-fertilized or often cross-fertilised crop species. According to Bateman (1947) the extent of genetic contamination in seed fields due to natural crossing depends upon the following factors: \(a) The breeding system of species. \(b) Isolation distance. \(c) Varietal mass. \(d) Pollinating agent. As the isolation between varieties is increased the contamination generally decreases, although there may be small amounts of contamination over wide distances. Isolation of seed crops therefore is a primary factor in the seed production of crop plants cross-fertilized by wind or insects. The extent of contamination depends upon the direction of prevailing winds, number of insects present and their activity, humidity and temperature at the time of anthesis etc. In addition to these the mass of varieties involved is also important in the amount of contaminating influence. ***5. Minor genetic variations***. Minor genetic variations may still exist even in the varieties appearing phenotypically uniform and homogeneous at the time of their release. During later production cycle some of these variations may be lost because of selective elimination by the environment. The loss or gain of certain of these may be sufficient to affect yields in one or the other way. To overcome these De Hann (1953) has suggested yield trials of lines propagated from plants of breeder's seed in the maintenance of self-fertilized crop varieties. Minor genetic variability may be a constant feature in often cross-fertilized crop species. Care during maintenance of nucleus and breeder's seed is necessary in such cases. ***6. Selective influence of diseases.*** The selective influence of diseases in varietal deterioration is also of considerable importance. New crop varieties often become susceptible to new races of diseases often caused by obligate parasites and are out of seed programmes. Similarly the vegetative propagated stocks deteriorate fast if infected by viral, fungal and bacterial diseases. During seed production it is, therefore, very important to produce disease-free seeds/stocks. No doubt, a more organized effort is required to check various diseases and produce seeds under disease-free conditions. ***7. Techniques of plant breeder.*** In certain instances, serious instabilities may occur in varieties due to cytogenetical irregularities not properly assessed in the new varieties prior to their release. Premature release of varieties, still segregating for resistance and susceptibility to diseases or other factors may also be important in the deterioration of varieties. This could be looked upon as the failure of the variety testing programmes. In addition to the factors discussed above, other factors, such as, break down in male sterility, certain environmental conditions, and other heritable variations may considerably lower the genetic Purity. **Maintenance of Genetic Purity during Seed Production** The methods suggested by Home (1953), and Hartmann and Kester (1968) may be used wholly or in part to maintain high levels of genetic purity during seed production. The various steps suggested by Home (1953), to maintain varietal purity, are as follows: 1. Use of approved seed only in seed multiplications. 2. Inspection and approval of fields prior to planting. 3. Field inspection and approval of growing crops at critical stages for verification of genetic purity, detection of mixtures, weeds, and for freedom from noxious weeds and seed-borne diseases, etc. 4. Sampling and sealing of cleaned lots. 5. Growing of samples of potentially approved stocks for comparison with authentic stocks. The various steps suggested by Hartmann and Kester (1968) for maintaining genetic purity are as follows: 1. Providing adequate isolation to prevent contamination by natural crossing or mechanical mixtures. 2. Roguing of seed fields prior to the stage at which they could contaminate the seed crop. 3. Periodic testing of varieties for genetic purity. 4. Avoiding genetic shifts by growing crops in areas of their adaptation only. 5. Certification of seed crops to maintain genetic purity and quality of seed. 6. Adopting the generation system. 7. Grow out tests The mechanics of maintaining genetic purity are further strengthened by the generation system. In this system, the seed production is restricted to four generations only. Starting from breeder's seed, the seed can only be multiplied up to three more generations, i.e., foundation, registered and certified. The mechanics of seed certification has been discussed in Chapters 31 to 33.The important safeguards for maintaining genetic purity during seed production thus are : **(a) Control of Seed Source.** The use of seed of an appropriate class and from an approved source is necessary for raising a seed crop. Four classes of seeds, namely, breeder's, foundation, registered and certified, are generally recognized in seed certification. The classes are given below as defined by the Association of Official Seed Certifying Agencies (AOSCA): ***Breeder's seed.*** Breeder's seed is seed or vegetative propagating material which is directly controlled by the originating or in certain cases, the sponsoring breeder or institution and which provides for the initial and recurring increase of foundation seed. ***Foundation seed.*** Foundation seed including 'select' in Canada, is seed stock so handled as to most nearly maintain specific genetic identity and purity and that may be designated or distributed by an agricultural experiment station. Production must be carefully supervised or approved by representatives of the station. Foundation seed is the source of all other certified seed classes, either directly or through registered seed. **Registered seed.** Registered seed is the progeny of foundation or registered seed that is so handled as to maintain satisfactory genetic identity and 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.** Certified seed is the progeny of foundation, registered or certified seed that is so handled to maintain satisfactory genetic identity and purity and that has been approved and certified by the certifying agency. **(b) Preceding Crop Requirements.** This has been fixed to avoid contamination through volunteer plants and also the soil borne diseases. **(c) Isolation.** The isolation of seed crops from various sources of contamination is also a necessary requirement for raising seed crops. Contamination may be due to natural crossing with other varieties grown alongside and off-types present in the seed field; contamination due to mechanical mixtures at the time of sowing, harvesting, threshing, processing and handling of seeds; and, contamination due to seed-borne diseases from nearby fields. Protection from these sources of contamination is necessary for maintaining genetic purity and the good quality of the seed.Isolation is required during raising of a seed crop to avoid contamination due to natural crossing and disease infection, by wind and insects from neighbouring fields; and also during sowing, harvesting, threshing and handling of seeds to avoid mechanical mixtures. Table 32.1-3 gives the isolation requirements necessary for producing foundation and certified seeds. **(d) Roguing of Seed Fields.** The existence of off-type plants, i.e., plants differing in their characteristics from those of the seed variety is another potent source of genetic contamination. All though a low percentage of such plants may not seriously jeopardise the genetic purity of the variety, their continued presence would certainly deteriorate the genetic purity of the variety. The removal of such plants is referred to as 'roguing'. There are three main sources of off-types. Firstly, the off-type plants may arise due to presence of some recessive genes in heterozygous conditions at the time of release of varieties. The recessive genes may also arise by mutation. The heterozygous plants segregate for the characters affected by the particular gene/genes in later production cycles and give rise to off-types. Another, source of off-type plants is the volunteer plants arising from accidentally planted seed or from seed produced by earlier crops. For this reason, the fields for producing seed of a particular variety should not have grown a potentially contaminating variety for a specified number of proceeding years.Mechanical mixtures as described earlier also constitute the major source of breakdown in genetical homogeneity.Off-type individual plants should be rogued out of the seed production fields before pollination occurs. Regular supervision by trained personnel is imperative. In other instances, it may be necessary. To control certain seed-borne diseases. **(e) Seed Certification.** The genetic purity in commercial seed production is often maintained through a system of seed certification. The principal objective of seed certification is to maintain and make available crop seeds, tubers, or bulbs and some-times turf grasses which are of good seeding value and true to variety. To accomplish these purposes, qualified and well experience personnel of seed certification agency carry out field inspections at appropriate stages of crop growth. They also make seed inspections to verify that the seed crop/seed lot is of the requisite genetic purity and quality, after harvesting to verify quality, and at the processing plants draw samples for seed testing and sometimes for grow-out tests also. In addition to inspections, seed certification agency also lay down the field and seed standards to which the seed crop and seed lot respectively must conform to get approval as certified seed. The field standards include land requirements, isolation requirements maximum permissible off-type, shedding tassels (in case of hybrid maize production), etc.The genetic purity of seed is thus assured if the certification agency has approved the seed. Seed certification implies that both the seed crop and seed lot have been duly inspected and that they meet requirements of good quality pedigree seeds. **(f) Grow-out Tests.** Varieties being grown for seed production / periodically be tested for genetic purity by grow-out tests, to make sure that they are being maintained in their true form.