General principles of Seed Production

Production of genetically pure and otherwise good quality pedigree seed is an exacting task requiring high technical skills and comparatively heavy financial investment. During seed production strict attention must be given to the maintenance of genetic purity and other qualities of seeds in order to exploit the full dividends sought to be obtained by introduction of new superior crop plant varieties. In other words, seed production must be carried out under standardized and well-organized condition.

Genetic Principle

  1. Deterioration of varieties: Genetic purity (Truness to type) of a variety can deteriorate due to several factor during production cycles. The important factors of apparent and real deterioration of varieties) are as follows:

  1. Developmental variation: When the seed crops are grown in difficult environment, under different soil and fertility conditions, or different climate conditions, or under different photoperiods, or at different elevation for several consecutive generations, the developmental variation may arise some times 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. Often the seed produce of all the varieties are kept on same threshing floor, resulting in considerable varietal mixture. To avoid this sort mechanical contamination it would be necessary to rogue the seed fields, and practice the utmost care during the 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 mutation.

  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

Natural crossing occurs due to following three reasons

  1. Natural crossing with undesirable types .

  2. Natural crossing with diseased plants.

  3. Natural crossing with off- type plants.

Natural crossing occurs due to following factors

  1. The breeding system of species

  2. Isolation systems

  3. Varietal mass

  4. Pollinating agent

  1. Minor genetic variations: Minor genetic variations may exist even in the
  2. Varieties appearing phenotypically uniform and homogeneous at the time of their release. During later production cycle some of this variation may be lost because of selective elimination by the environment. To overcome these yields trials are suggested .

    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 vegetatively 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.

  3. Techniques of plant breeders: In certain instances, serious instabilities may occur in varieties due to cytogenetically irregularities not properly assessed in the new varieties prior to their release. 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 various steps suggested), to maintain varietal purity, are as follows.

  1. Use of approved seed only in seed multiplication.

  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 for maintaining genetic purity are as follows:

  1. Providing adequate isolation to prevent contamination by natural crossing or mechanical mixtures
  2. Rouging 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 in 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.

Agronomic principles

  1. Selection of a Agro-climatic Region
  2. A crop variety to be grown for seed production in an area must be adapted to the photoperiod and temperature conditions prevailing in that area.

  3. Selection of seed plot
  4. The plot selected for seed crop must be free from volunteer plants, weed plants and have good soil texture and fertility The soil of the seed plot should be comparatively free from soil borne diseases and insects pests.

  5. Isolation of Seed crops
  6. The seed crop must be isolated from other nearby fields of the same crops and the other contaminating crops as per requirement of the certification standards.

  7. Preparation of Land
  8. Good land preparation helps in improved germination, good stand establishment and destruction of potential weeds. It also aids in water management and good uniform irrigation.

  9. Selection of variety
  10. The variety of seed production must be carefully selected, should possess disease resistance, earliness, grain quality, a higher yielder, and adapted to the agroclimatic conditions of the region.

  11. Seed treatment:
  12. Depending upon the requirement the following seed treatment may be given

  1. Chemical seed treatment.
  2. Bacterial inoculation for the legumes.
  3. Seed treatment for breaking dormancy.
  1. Time of planting
  2. The seed crops should invariably be sown at their normal planting time. Depending upon the incidence of diseases and pests, some adjustments, could be made, if necessary.

  3. Seed Rate
  4. Lower seed rates than usual for raising commercial crop are desirable because they facilitate rouging operations and inspection of seed crops.

  5. Method of sowing
  6. The most efficient and ideal method of sowing is by mechanical drilling.

  7. Depth of sowing
  8. Depth of sowing is extremely important in ensuring good plant stand. Small seeds should usually be planted shallow, but large seeds could be planted a little deeper.

  9. Rouging: Adequate and timely rouging is extremely important in seed production. Rouging in most of the field crops may be done at many of the following stages as per needs of the seed crop.
  1. Vegetative / preflowering stage

  2. Flowering stage

  3. Maturity stage

  1. Supplementary pollination

Provision of honey bees in hives in close proximity to the seed fields of crops largely cross pollinated by the insects, ensure good seed set thereby greatly increase seed yields.

     13 .Weed control: Good weed control is the basic requirement in producing good               quality seed. Weeds may cause contamination of the seed crop , in addition to               reduction in yield:

     14. Disease and insect control: Successful disease and insect control is another               important factor in raising healthy seed crops. Apart from reduction of yield,               the quality of seeds from diseased and insect damaged plants is invariably               poor.

  1. Nutrition:
  2. In the nutrition of seed crops, nitrogen, phosphorus, potassium, and several other elements play an important role for proper development of plants and seed. It is, therefore, advisable to know and identify the nutritional requirements of seed crops and apply adequate fertilizers.

  3. Irrigation
  4. Irrigation can be important at planting for seed crops on dry soils to ensure good uniform germination and adequate crop stands. Excess moisture or prolonged drought adversely affects germination and frequently results in poor crop stands.

  5. Harvesting of Seed crops:
  6. It is of great importance to harvest a seed crop at the time that will allow both the maximum yield and the best quality seed.

  7. Drying of seeds:
  8. In order to preserve seed viability and vigour it is necessary to dry seeds to safe moisture content levels.

  9. Storage of raw seeds: The best method of sowing seed for short periods is in sacks or bags in ordinary buildings or godowns.


Ag.
Technologies
(Seeds)