In this article we will discuss about:- 1. Germination of Seed 2. Genetic Purity of Seeds 3. Types of Pure Seeds 4. Seed’s Viability Test 5. Seed Dormancy 6. Seed Treatment 7. Seed Plot Technique of Potato 8. National Seed Corporation (NSC) 9. State Seed Corporation (SSC).
Contents:
- Germination of Seed
- Genetic Purity of Seeds
- Types of Pure Seeds
- Seed’s Viability Test
- Seed Dormancy
- Seed Treatment
- Seed Plot Technique of Potato
- National Seed Corporation (NSC)
- State Seed Corporation (SSC)
1. Germination of Seed:
Seed is defined either Agronomically or Botanically. Agronomically a seed or seed material or propagule is living organ of the crop in rudimentary from that is used for propagation or in other words, any part of the crop from which a new crop will grow.
Botanically seed is a fertilized ovule consisting of intact embryo, stored food and seed coat which is viable and has got the capacity to germinate.
Agronomically germination means the capacity of seeds to give rise to normal sprouts within a definite period fixed for each crop under optimum field conditions.
Four essential factors for germination of seeds:
(i) Capacity of seed to germinate
(ii) Moisture
(iii) Temperature
(iv) Oxygen-supply.
Factors governing growth of plants:
(i) Parental feature
(ii) Air
(iii) Moisture
(iv) Temperature
(v) Light
(vi) Minerals.
Field germination is always lower than the germination of seeds tested in Laboratory. The mortality of seedlings after germination in the field frequently depends upon entomological, phytopathological, edaphological and meteorological factor as well as toxic effects of organic secretions and applied chemicals and storage period of the seed i.e. ageing.
Factors affecting the emergence of seedlings are:
1. Deep sowing or depth of soil cover over the seed.
2. Inadequate or excess soil moisture.
3. Poor aeration.
4. Higher soil compaction or impermeable layer of soil or outer materials.
5. Low temp.
6. Rapid desiccation of soil.
7. Longer time period.
8. Injurious level of salt content.
9. Poor seed capacity.
10. Detrimental physical, chemical and biological soil conditions.
Germination of seeds depends upon their natural peculiarities and biological conditions e.g. – for the purpose of seed production, sunflower, mustard and flax can be harvested 15-20 days earlier and coriander 10 days earlier than for market purposes.
Foliar feeding of N at the grain filling stage improves germination, initial growth and growth vigour of seedlings and weakens dormancy.
Chemical Ripener, e.g.- Magnesium chlorate @ 20 kg/ha can be applied on sunflower 40 days after flowering to reduce the moisture content of seeds twice without affecting the sowing quality.
Seed Index:
Weight of 100 seeds (in case of bold seeds like maize).
Test Weight:
Weight of 1000 seeds (in case of small seeds like rice).
Seed Quality Index:
It is the vigour of seed germination.
Real Value of Seed:
It is the percentage of germinability of percentage of purity of seed lot of a crop plant.
RV is expressed in percentage and also known as Utility percentage of seed.
Conditions affecting the real value of seeds are the method of production, the method of handling and the method of storage. Seeds having a real value lower than 70% are usually not preferred for sowing purposes because of poor germination and purity values.
Impurity percentage is called Dockage.
2. Genetic
Purity of Seeds:
Genetic purity is required 100% as far as impurities by seeds of other varieties of same crop is concerned but in case of Impurity by seeds of other crop species; it is permitted upto 0.1% only.
Isolation Distance:
Isolation means to keep apart. Isolation distance is the specified distance from potential contaminants, where an acceptable level of contamination is expected. Isolation of seed crop is essential to avoid genetic & physical impurities. Genetic purity i.e. varietal purity may be deteriorated by cross – pollination from the plants of nearby plots. Physical impurities may occur due to physical or mechanical admixture with other crop species or other varieties of the same species from the nearby plots.
Therefore the protection from these sources of contamination is necessary for maintaining genetic and physical purity i.e. good quality of the seed. Isolation distance is affected by mode of pollination (i.e. self-pollination or cross pollination), pollination activity as well as direction and velocity of wind. Essentially self- pollinated crops like rice, wheat & soybean have only 3 metre as isolation distance. The increase in natural cross pollination percentage requires increasing isolation distance e.g.-
3. Types of Pure Seeds:
There are four classes recognized by the International Crop Improvement Association.
1. Breeder/Nucleus Seed:
Such seeds are produced directly under the supervision of plant breeder and possessed all the required genetic characters. Such seeds have high genetic value and are costly due to very little in quantity. It may be produced by the breeder’s concerned Institution when breeder is not available. Breeder seed is used to produce foundation seed. In case of self-pollinated species, mass selection may be regularly practiced to retain the genetic purity of the variety.
2. Foundation Seed:
It is produced from breeder seed and is the source of all other certified seed classes either directly or through registered seed. It is also known as Mother seed. Production of foundation seed is the responsibility of National Seeds Corporation. It is produced on Government farms, at experiment stations, Agriculture Universities or on cultivator’s field under strict supervision of research scientists and experts from NSC or SSC. It has specific genetic identity and purity. White tag denotes foundation seed.
3. Registered Seed:
Produced from FS or Registered seed itself. It is the parent of certified seed or RS. It has satisfactory genetic identity and purity and is usually produced by progressive farmers under technical guidance and supervision from SSC. It is often omitted and certified seed is produced directly from FS. It is general practice in India. It has purple tag.
4. Certified Seed:
Progeny of RS, FS or CS itself. It has satisfactory genetic identity and purity. It is approved and certified by the state seed certifying agency, annually produced by progressive fanners according to standard seed production practices. It has blue tag. It is available for general distribution to farmers for commercial crop production. It is generally produced by SSC but NSC also undertakes its production, if required. Two classes of CS are produced i.e. F1 and F2 Recertification is not permitted from F2 generation (second) of seeds.
Other types of seeds in Agronomic use are:
(a) Improved Seed:
It is a better seed substitute for pure seed but is not so good with respect to genetic and physical factors. It has at least 10-15% more genetic potential than the local seed and are resistant to pest and diseases, well adapted to agro-climatic conditions of the locality, high in response to better condition of growth.
(b) Hybrid seed.
(c) Composite seeds.
(d) Mutant seeds.
4. Seed’s Viability Test:
Seed’s viability is defined as the capacity of the seed to remain capable of germination for some specific period of time. When the seeds are dormant or very slow in germination, the rapid test is extremely useful.
1. Respiration Test:
Respiration is an indication of life but such tests are complicated.
2. Electrical Conductance Method:
Seeds are soaked in distilled water and electrical conductance of such water is tested. The increase in conductance is roughly proportional to the percentage of dead tissues. The increase in the conductivity is due to leaching of metabolites from dead seeds.
3. Potassium Permanganate Method:
It is a qualitative test to find out whether seeds are viable. Increase in the proportion of dead seed increase the discolouration of the solution since leaching from living cells is very less.
4. Indigocarmine Method:
Portion of dead seeds is determined by counting the number of stained.
5. Embryo Culture Method:
It takes about 7-10 days, judged by counting the number of germinated embryos.
6. Tetrazolium Chloride Test:
This test is known as Biological test. Seeds are soaked in 0.5-2% solution of 2, 3, 5 triphenyl tetrazolium chloride. The viable or living seeds take bright colouration and the colouration becomes more intense in the embryo. It can be made quicker by cutting kernels, using vacuum and maintaining a temperature of 40-45°C, it takes only 4-5 minutes to complete a test of 100 kernels.
7. Grodex Test:
Grodex is a seed germination indicator and is a brand name of triphenyl tetrazolium bromide in powder form.
5. Seed Dormancy:
Dormancy is the arrested development and reversible rest period of plant organs either of a seed or of any vegetative part. The formation of dormant structures is commonly associated with the suspension of metabolic, synthetic and morphogenetic activities that are associated with the minimum physiological and a minimum moisture content. During this period, there is very poor or total suspension of respiration or rather anaerobic respiration with higher respiration quotient.
Dormancy is due to lack or inactivity of hydrolytic enzymes. Gibberellins are the predominant germination agents found in the germination phase during the food reserve degradation stage. Cytokines exert their influence later on the initiation of cell proliferation and expansion. Red light (660mu) promotes and blue specially far-red light (735mu) inhibits germination.
Dormancy can be broken artificially by various special treatments which may be grouped into two groups:
1. Heat treatment at 40-45°C for different duration.
2. Low temp, treatment at 2-8°C for 12-24 hours but seeds should be presoaked for 36 hours before they are given the low temperature treatment.
3. Alternate heating and cooling for several times.
4. Alternate drying and wetting for several times.
5. Exposure for 24 hours of water soaked seeds to red light for 1-2 hrs. at 15-25°C temp.
6. Dehusking or removal of seed coats (scarification) by rubbing to make it permeable to water.
(a) Inorganic Chemicals:
(i) By Acid Treatment:
Dilute solutions of HNO3, HCl or H2SO4 (0.1- 0.5%) for different durations in minutes.
(ii) KNO3 (1-3%):
Strongest and used for immediate dormancy break after harvesting; NH4NO3(1-3%). H2O2, H3BO4 etc.
(iii) By Gases:
By increasing O2 concentration.
(b) Organic Chemicals:
(i) Non-hormonal Thiourea, Ascorbic acid.
(ii) Hormonal:
GA3 (1-1000 ppm) — Commonly used hormone to break dormancy; Others are Kinetin (1-100ppm), Ethylene (Ethrel solution of 100-300 ppm).
Dehumidification:
Removal of water – vapour from the air in storage. Silica gel is the most common desiccant used as chemical dehumidifier.
Tempering:
Process of bringing grains or other products to a de sired moisture or temperature for processing.
Matrical is the heterogeneity in the quality due to location of the seeds in the inflorescence e.g. difference in flowering pattern.
Indian seeds act passed in 1966.
6. Seed Treatment:
Besides breaking seed dormancy, seed treatment is also done before sowing the seeds for the following purposes:
1. To protect from seed borne and soil borne diseases and insect pests damage.
2. To promote germination.
3. To hasten nitrogen fixation capacity in case of pulses.
4. For easy sowing.
(A) Treatment for Diseases and Insects Control:
(i) Hot Water Treatment:
Seeds are kept in hot water at a certain temp, for certain period.
Later on, after cooling in cold water such seeds are dried in shade. This method is successful in controlling following diseases— Loose smuts of Wheat (54°C for 10 minutes), Loose smuts of Barley (54°C for 13 minutes), Alternaria blight of Wheat (38°C for 10 minutes), Leaf spot of Til (54°C for one hour)
(ii) Solar Treatment:
After soaking the seeds in water for some hours, seeds are dried in scorching sun in the month of May-June by keeping on cemented floor or metal-sheet. This method is used to control loose smuts of Wheat and Barley.
(b) Chemical Treatment:
Different fungicides e.g. Agrosan G.N., Ceresan, Captan, Thiram etc. are used for the same.
(B) Seed Inoculation in Legumes:
Before sowing the legumes crops in the new area, the legume seeds are to be inoculated with Rhizobium culture.
7. Seed Plot Technique of Potato:
Objective:
To produce seeds free from virus Y, A, X and S. These viruses are transmitted by aphids. Aphid population is low in hills during April to August while it is low in the plains during October to early January.
Nucleus seed of potato is produced in the hills during April to August when aphid population is low. It is brought to plains and is stored in cold storage for planting the seed crop in October.
The seed production practices are:
1. Start with disease free seed stocks.
2. Select suitable location i.e. aphids free during crop growth.
3. Adopt lands isolation and other requirement of certified seed production.
4. Rogueing and inspection of crops.
(a) Timely planting i.e. first week of Oct.
(b) Raising the crop on not too rich soil i.e.no judicious manuring and heavy fertilization.
(c) Seeds are planted closely and use of pre-sprouted tubers.
(d) Restricted irrigation after the crop has been tuberised well, with hold irrigation 10-15 days before. Restrict the irrigation by middle of December and gradually by end of December.
(e) Haulms should be dried up by the middle of January. The haulms should cut or wilt before aphid build up population by the end of Jan. If the crop is still green, kill the haulms with a 2% solution of CuSO4 or cut green haulms to prevent transmission of viruses to tubers.
(f) Tubers are allowed to remain in the soil upto the end of Feb. or early March or may be spread thinly after harvesting in a dark place to allow thickening of skin of potato.
(g) Tubers are harvested, graded and kept in cold storage to serve as seed for the next year’s commercial crop. One ha of seed crop produces enough seed for 10-15 ha of commercial crop.
8. National Seed Corporation (NSC):
NSC was registered in 1963 having two main objectives:
1. To promote development of a seed industry in India.
2. To produce and supply foundation seeds of various crops.
9. State Seed Corporation (SSC):
SSC’s are chiefly concerned with production and supply of certified seed.
To reduce the work load of NSC and to stimulate a faster growth of industry, SSCs were established in view of great success of and the impact made by the tarai development corporation (TDC) , Pantnagar.
State Seed Certification Agency:
It is responsible for seed certification, SSCA makes field inspections and conducts seed tests required for seed certification.
The seed Act, was enacted by the parliament on 29.12.1966 and the seeds Rules were notified in 1968. This Act came into force throughout the country on 2nd Oct. 1969. Seed was declared as an essential commodity under the Essential Commodities Act. (1955)