1. SEED SCIENCE &TECHNOLOGY
Principles of Seed Production 2
Dr. K. Vanangamudi
Formerly Dean (Agriculture), TNAU, Coimbatore.
Dean, Adhiparasakthi Agricultural College,
Professor & Head,
Seed Science & Technology, TNAU, Coimbatore.
Agronomic principles Completed in Principles of Seed Production 2
Varietal seed production principles
1. Hybrid seed production
1.1. Planting ratio
Ratio to be maintained between female and male lines in order to have good amount of
pollen grains for proper pollination and fertilization.
E.g. Rice - 8:2 to 10:2 (Female : Male)
Maize – 4:2
Sunflower hybrid seed production is 4:1.
Cotton (block system) - female and male are raised in a ratio of 8:1 in separate
blocks not more than 5 m distance. Hybrid seed production is by emasculation and
dusting.
2. 1.2. Border rows
Seed field should be planted with border rows all the four sides with male parent
seeds to have more pollen source and avoid contamination.
Number of border rows - 4 to 12
1.3. Synchronized flowering
Uniformity of flowering between parental lines.
To achieve uniformity, any one of techniques can be done.
Staggered sowing
Withholding irrigation
Application of urea or DAP
Staggered sowing
Adjusting sowing time of parental lines in order to have synchronized
flowering between parental lines for proper seed set.
Early flowering line should be sown later.
3. E.g. Sunflower KBSH -1 hybrid seed production; male parent is late flowered by 6
days than the female.
So, sowing of male line 6-D-1, 6 days earlier than female line ensures
synchronized flowering.
Rice - exertion of female panicle from boot leaf is a problem.
Spray GA3 @ 70-75 g/ha twice during flowering time.
Since GA is cell elongation factor, it aids in exertion of panicle.
1.4. Special techniques for hybrid seed production
Detasseling: Removal of tassel from the female row in maize.
Emasculation and dusting: Done at proper time of flowering to have good yield and
also to avoid contamination in cotton.
Not followed in the case of crops where hybrid is produced by utilizing male sterility
system, e.g. sunflower.
1.5. Supplementary pollination
To have good seed set.
Rice: Rope pulling or rod driving.
4. Sunflower: Rubbing or installation of bee hives.
1.6. Genetic contaminants
Off types: Deviant of seed plant. Common for varieties and hybrids.
Pollen shedders: Presence of B line in A line of hybrid seed production. Eg. Rice.
Pollen Partials – Bajra
Shedding tassel: Presence of tassel in the female row of maize
Selfed bolls: Cotton - selfed bolls without emasculation and dusting.
Selfed fruits: in the case of other vegetables.
1.7. Method of harvest
Hybrids - harvest R line first, remove produce from field and do one final rouging in
female row and do harvest.
2. Genetic principles
2.1. Maintenance of genetic purity during seed production
Various steps suggested by Home (1953), to maintain varietal purity
Use of approved seed
Inspection and approval of fields prior to planting.
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.
Sampling and sealing of cleaned lots.
Growing of samples of potentially approved stocks for comparison with authentic
stocks.
5. Various steps suggested by Hartmann and Kester (1968) for maintaining genetic purity
Providing adequate isolation
Roguing
Periodic testing of varieties for genetic purity.
Avoiding genetic shifts by growing crops in areas of their adaptation only.
Certification of seed crops to maintain genetic purity and quality of seed.
Adopting the generation system.
Grow out tests
2.2. The important safeguards for maintaining genetic purity during seed production are
1. Control of seed source
Use of seed of an appropriate class of seed and from an approved source
2. Preceding crop requirements
To avoid contamination through volunteer plants and also soil borne diseases.
3. Isolation
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.
4. Roguing of seed fields
Existence of off-type plants, i.e., plants differing in their characteristics from those of
seed variety is another potent source of genetic contamination.
Three main sources of off-types:
May arise due to presence of some recessive genes in heterozygous
conditions at the time of release of varieties.
Volunteer plants arising from accidentally planted seed or from seed produced
by earlier crops.
Mechanical mixtures
5. Seed certification
Genetic purity in commercial seed production is often maintained through a system of
seed certification.
6. Principal objective of seed certification is to maintain and make available crop seeds,
tubers, or bulbs and some-times turf grasses.
To accomplish these purposes
Qualified and well experienced personnel of seed certification agency carry out
field inspections at appropriate stages of crop growth.
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.
Field standards - land requirements, isolation requirements, maximum permissible
off-type, shedding tassels (in case of hybrid maize production).
Seed certification implies that both the seed crop and seed lot have been duly
inspected.
6. Grow-out tests
Periodically tested for genetic purity by grow-out tests