What is Seed Dormancy its causes and How it is significant for Agricultural Crops?
Definition:
Dormancy is a delaying mechanism which prevents seed germination under conditions which might prove to be unsuitable for germination.
Types of Seed Dormancy:
Three types of seed dormancy depending on the how each of them arises: viz.
innate, enforced and induced.
- Innate dormancy:
A seed which is incapable of germination when freshly dispersed even if conditions suitable for seedling growth are supplied. This inability to germinate may be due in certain species to the embryo being immature at the time of dispersal. May be by the presence of inhibitory compounds either in the seed coat or in the embryo.
- Enforced dormancy:
It occurs when the seed is simply being deprived of its requirements for germination, for example, by the absence of sufficient moisture, oxygen, light or a suitable temperature. No special physiological mechanism is involved here, and the seeds might more properly be considered merely quiescent. Seeds lying deep in the soil are probably prevented from germination by a lack of oxygen.
iii. Induced dormancy:
It is caused by the unfavourable conditions. In many species newly dispersed seeds have no innate dormancy, but if they fail to meet suitable conditions for germination, they acquire an induced (or secondary) dormancy.
Causes of Seed Dormancy:
The major causes of seed dormancy are following:
- Hard seed coat:
The hard seed coat is impermeable to water and oxygen.
- Immature embryo:
In some species the embryos are incompletely developed when seeds are shed. In such cases embryos mature during the dormant period.
iii. Presence of inhibitors:
Inhibiting chemicals in the fruit or seed coats or within die embryo or endosperm, may delay germination.
- light:
Light sensitive seeds do not germinate in absence of light; whereas light hard seeds do not germinate on the exposure to light.
- Temperature:
Generally the low temperatures promote and high temperatures inhibit the germination. In the Indian desert many weed seeds must pass through very high temperature (60°-70C) of sand in day and at the same time low temperatures (5°-10°C) of night before they are stimulated for germination.
Role of Seed Dormancy:
- The ability to remain dormant for a long period is associated with seeds of species from unpredictable environments such as bare ground and swamps.
- Prevent germination of all seed at same time.
- No constraints while storage the seed.
Due to this feature, food is easily available whole the year especially for those countries where grans are used as a staple food.
- Easy transportation of seed over long distances.
This is important for trade and international transportation.
- Make sure the dispersal of seed.
- The absence of dormancy would appear to be a disadvantage to any species as it reduces the opportunities for dispersal even in predictable environments.
- Dormancy is necessary in arid zone plants.
- It sure the survival of seed plants on the earth.
Fahim Ali Jawad
Centre of Agricultural Biochemistry and Biotechnology, UAF
