Genetic Purity during Seed Production
The various steps suggested by Hartmann and Kester (1968) for maintaining genetic purity.
The steps are
Providing adequate isolation to prevent contamination by natural crossing or mechanical mixtures.
Rouging of seed fields, prior to the stage at which they could contaminate the seed crop
Periodic testing of varieties for genetic purity
Avoiding genetic shift by growing crops in areas of their adaptation only.
Certification of seed crops to maintain genetic purity & quality seed.
Adopting generation system. (the seeds produced is restricted to four generation only i.e. starting from breeders seeds.) and the seeds can be multiplied up to three more generations i.e. foundations, registered and certified.
Grow-out – tests: The important factors / safeguards for maintaining genetic purity during seed production are
Control of seed source:
For raising a seed crop the seeds should be required from an approved source and from an appropriate class is necessary.
Four classes of seeds are generally recognized in seed certification namely breeder seed, foundation registered and certified. These classes are recognized by AOSCA i.e. Association of official seed certifying agencies.
Breeder’s seed: Is a seed or vegetative propagating material which is directly controlled by sponsoring breeder of institution & which provides increases of foundation seeds.
Foundation seed: is a seed stock so as to maintain specific genetic identity and purity and may be designated or disturbed by agriculture experiment station. Production must be carefully supervised 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 progenies of foundation and it is handled so as to maintain genetic identity and purity and that has been approved by and certified by certifying agencies.
Certified seed: Is the progeny of foundation, registered or certified seed, that is handled to maintain genetic identity and purity and that has been approved by and certified by certifying agencies.
Preceding Crop Requirements:
Preceding Crop Requirements has been fixed to avoid contamination through volunteer plants and also from soil borne diseases. (Volunteer plants mean plants grown in the field from previous crops).
Isolation is required during seed crop production to avoid contamination due to natural crossing and diseases infection by wind and insects from neighboring field and also during sowing, harvesting, threshing and handling of seeds to avoid mechanical mixtures.
The isolation distance is different from crop to crop and from different classes of seeds. i.e. certified seeds & foundation seed plots
Rouging of seed fields:
The off time plants i. e. plants offering in their characteristic from those of the seeds variety is another source of genetic contamination. Their continued presence would certainly deteriorate the genetic purity of the variety. The removal of such type of plant is referred as “rouging”.
There are three main sources of off- type
The off-type plant may be arises due to presence of recessive genes in heterozygous condition at the time of release of variety. (The recessive genes may also arise by mutation).
Off-type plants are due to volunteer plants or from seed produced by earlier crop.
Mechanical mixtures also constitute the major source foe off- type plants.
The genetic purity in commercial seed production is maintained through a system of seed certification.
The objective of seed certification to maintain and make available crop seeds, tubers, bulbs, etc. which are of good seeding value and true to variety for seed certification purpose well experienced and qualified personal are required from seed certification agency & they carry out field inspection at appropriate stage of crop growth. They also make seed inspection variety the seed crop/seed lot is of the requisite genetic purity and quality.
After harvest crop they variety the quality and at the processing plants they take samples for seed testing and also for grow-out-test.
Grow- out – test:
Varieties being grown for seed production should periodically be tested for genetic purity by grow – out – test, to make sure that, seed being maintained in their true form.
When a farmer buy a seed from any recognized institute or company, he expect to receive a good quality seed and not a mixture of other crop seed, weed seeds, straw etc. It is not possible to remove all these admixtures completely with the use of cleaning machine is & some seeds always remain present and there is necessary to take purity test or analysis, to determine how much % of the admixture is present in the seed.
To avoid admixture in seed of a particular variety or crop the buyer can be protected by the seed regulation laws or acts in many countries, for this purpose in many countries “seed testing stations or seed testing laboratory” are set up & these stations or laboratory are associated with ISTA (International seed testing association)