In this article we will discuss about:- 1. Definition of Seed Dormancy 2. Reasons of Seed Dormancy 3. Natural Breaking 4. Artificial Breaking 5. Importance.
Definition of Seed Dormancy:
Seed dormancy or rest is the innate inhibition of germination of a viable seed even placed in most favourable environment for germination. Bewlay and Black (1994) have divided seed dormancy into two categories, seed coat based and embryo based. Germination inhibitors occur in both.
Reasons of Seed Dormancy:
1. Immaturity of Embryo:
Embryo is immature at the time of seed shedding. The seed will remain dormant till the embryo becomes mature, e.g., Anemone nemorosa, Ranunculus ficaria.
The seeds require a period of dry storage for developing the ability to germinate, e.g., Wheat, Oat, Barley.
3. Impermeable Seed Coat:
The seed coat is impermeable to water and gases, e.g., Apple, Chenopodium.
4. Hard Seed Coat:
The seed coat is mechanically resistant and does not allow the embryo to grow, e.g., Amaranthus, Lepidium.
5. Germination Inhibitors:
They occur in the seed coats and cotyledons of the embryos. The important germination inhibitors causing seed dormancy are abscisic acid, phenolic acid, ferulic acid, coumarin, short fatty acids and cyanogenic chemicals, e.g., Apple, Peach, Ash, Cucurbita, Iris, Xanthium.
Natural Breaking of Seed Dormancy:
In nature seed dormancy is broken automatically due to:
(i) Development of growth hormones to counter growth inhibitors,
(ii) Leaching of germination inhibitors,
(iii) Maturation and after-ripening of embryo,
(iv) Weakening of impermeable and tough seed coats by microbial action, abrasion, passage through digestive tract of animals, etc.
Artificial Breaking of Seed Dormancy:
Hard, impermeable seed coat is weakened or ruptured by filing, chipping, hot water and chemicals.
Seeds are moistened and exposed to oxygen for variable period at low or high temperature.
3. Counteracting Inhibitors:
Inhibitors are destroyed by dipping seeds in KNO3, thiourea, ethylene chlorohydrin and gibberellin.
4. Shaking and Pressure:
Vigorous shaking and hydraulic pressure are used to weaken seed coats.
Importance of Seed Dormancy:
Seed dormancy allows seeds to pass through drought, cold and other un-favourable conditions.
It is essential for dispersal of seeds.
3. Germination under Favourable Conditions:
Seeds germinate only when sufficient water is available to leach out inhibitors and soften the seed coats.
It is because of dormancy that human beings are able to store grains, pulses and other edibles for making them available throughout the year and transport to the areas of deficiency.