Lecture - 3 Types and dormancy of Seeds

 Lecture – 3 Seed types and dormancy of seeds

Definition: - Seed is technically defined as ripened ovule containing embryo. Another definition says that the seed is a living embryo which is vital and basic input for attaining sustained growth in agricultural production in different agro-climatic conditions.

The embryo in the seed remains almost suspended for sometimes and then revives to new development.

´  Nucleus seed: - This is the hundred percent genetically pure seed with physical purity and produced by the original breeder/ state agricultural university from basic nucleus seed stock.

´  Breeder seed: - This is the seed of a new variety that has the highest physical purity and genetically purity and directly provided by the breeder or his institution for further multiplication.

´  Breeder seed produced from nucleus seed under the supervision of a qualified plant breeder in a research institute of agricultural university.

´  The genetic purity of breeder seed should be maintained 100 percent.

    ´ A golden yellow color certificate is issued for this category of seed by the                  producing breeder. 

Foundation seed: - The progeny of breeder seed produced by seed producing agencies in public and private sector, under supervision of seed certification agencies in such a way that its quality is maintained according to prescribed field and seed standard.

´   It is also known as mother seed. It has specific genetic purity is 99.5 percent.

´  A white color certificate is issued for foundation seed by seed certification agencies.

´  Registered seed: - This is the progeny of foundation seed grown by the selected farmers to maintain genetic purity and identity and has undergone field and seed inspections to ensure conformity with standards.

´  A purple color certificate is issued for this category of seed.

´  Certified seed: - Certified seed is progeny of foundation seed and its production is supervised and approved by certification agency.

´  The seed of this class is normally produced by the state and national seeds corporation and private seed companies on the farms of progressive growers.

´  This is the commercial seed which is available to the farmers and its genetic purity should be 99 percent. 

´  A blue color certificate is issued by seed certification agency for this category of seed.

v  Characteristics of good seed

1.   It should be belonging to the proper variety of crop which is proposed to be grown.

2.   It should be free from mixture of other seed.

3.   It should be mature, well developed and plump in size.

4.   It should be high germination capacity.

5.   It should be free from pest and disease.

6.   It should be uniform in its text and outlook.

7.   Seed should be containing maximum amount of moisture (8-12%).

8.   Seed should be germinating rapidly and uniformly when sown.

Seed dormancy

          Seed dormancy is the failure of fully developed, mature, viable seed to germinate even under favorable physical conditions like moisture and temperature.

v  Kinds of dormancy in seed

1.   Primary dormancy: - The seeds which are capable of germination just after ripening even by providing all the favorable conditions are said to have primary dormancy. For example: Potato.

2.   Secondary dormancy: - Some seeds are capable of germination under favorable conditions just after ripening but when these are stored under unfavorable conditions even for few days, they become incapable of germination.

3.   Special types of dormancy: - Sometimes seed germinate but the growth of the sprouts is found to be restricted because of a very poor development of roots and coleoptiles.

v  Causes of dormancy

1.   Seed coats being impermeable to water: -

Ø         ´  Some seeds have a seed coat which is impermeable to water.

    ´ Such seeds even when fully matured and placed in favorable conditions fail to germinate because of failure of water to penetrate into the hard seed coats.

Ø       ´ These seeds become permeable, if they are treated with sulfuric acid or dipped in boiling water for few seconds. Example Cotton.

2.   Hard seed coat: -

Ø  ´ Seeds of mustard, Amaranths, etc. contain a hard and strong seed coat which prevents any appreciable expansion of embryo. 

   ´ Thus, if the seed coat fails to burst the embryo will remain dormant even after providing all the favorable conditions for germination.

3.   Seed coat being impermeable to oxygen: -

Ø      ´ The seed coats are impermeable to oxygen and if the seed coats do not rupture the seeds fails to sprout due to deficiency of oxygen.

4.   Rudimentary embryo of seeds: -

Ø ´ The seeds which are apparently ripened contain a rudimentary or imperfectly developed embryo and the germination of such seeds naturally gets delayed until the embryo develops properly.

5.   Dormant embryo: -

Ø   ´  The seeds of an apple, peach, Pinus, etc. do not germinate even though the embryos are completely developed and all the favorable conditions for germination     are provided.

Ø  ´  In such seeds, physiological changes called after ripening take place during the period of dormancy which enables the seeds for germination.

6.   Synthesis and accumulation of germination inhibitors in the seeds: -

Ø     ´  Plant organs synthesize some chemical compounds which are accumulated in the seeds at maturity and these chemicals inhibit the germination of their seeds.