Seed Dormancy

Abstract

Seed dormancy is a failure of viable, intact, and mature seeds to germinate under favorable environmental conditions which may last from few days to several months depending on their habitat and growth conditions. It is also apparent that dormancy is more common in undomesticated species as compared to the species which have been domesticated to a large scale. Extensive breeding followed by the selection for desirable traits of early germination and rapid plant establishment has played a major role in eliminating dormancy that prevailed in the seeds of their wild ancestors. However, the fact that presence of dormancy up to a certain extent is always desirable to avoid great damage to seed quality due to pre-harvest sprouting or vivipary necessitated the deliberate selection of this character in cultivated species. Classification system of dormancy in seed is primarily based on the embryo and seed coat factors which divided dormancy into five broad groups, viz., morphological dormancy, physiological dormancy, morpho-physiological dormancy, physical dormancy, and combinational dormancy. Abscisic acid (ABA) also plays a significant role in the mechanism of dormancy and is considered as the most important germination inhibitor. Also, the accumulation of different phenolic compounds, viz., phenolic acids, flavonoids, tannins, etc., in the seed covering structures strongly inhibits the germination of some cereals like wheat, barley, sorghum, etc. Temperature and light also contribute in regulating seed dormancy. Although gibberellic acid is not directly involved in the control of dormancy, it promotes and maintains the germination in seeds, and its ratio to abscisic acid has always been a critical parameter in determining the state of dormancy. Although natural breakdown of seed dormancy may occur in some seed species, different chemical and mechanical seed treatments are also required for the successful termination of seed dormancy.