Some seeds are capable of germinating as soon as certain necessary environmental conditions are satisfied. A seed of this type is said to be quiescent until germination begins. Other seeds go into a more prolonged resting period, during which they will not germinate., even if all the usual environmental requirements are satisfied. A seed of this type is said to be dormant.
Dormancy refers to a condition in a viable seed which prevents it from germinating when supplied with the factors normally considered adequate for germination. It is common with wild crop specie
During the dormancy period, the chemical and biochemical activity are low, therefore has a longer shelf life. Seed dormancy is a strategy for the survival of wild seed, weed seeds etc which germinate at different time.
Causes of seed dormancy and how to overcome it
Impermeable seed coat:
This is an example of structural constraint in germination of seeds. The seed coat may be impermeable to water and gases, thus limiting metabolic activity in the seed. Impermeability may be caused by deposition of various substances in the restaurant, pericarp or nuclear membrane. In such a case, water and oxygen cannot enter the seed and carbon dioxide cannot escape. Dormancy of this type is broken when the testa becomes less resistant. Such methods include mechanical or chemical scarification. Mechanical scarification involves piercing or scraping of seed testa before seeds are sown. Chemical scarification could be done by soaking seeds in chemical such as dilute sulphuric acid, hydrochloric acid, sodium hydroxide, alcohol, acetone for few minutes. Treatment of seeds in boiling water may also break dormancy. Chemical scarification is limited by the following: The materials may be dangerous to handle, over treatment of seeds with chemical may reduce germination or kill the embryo. Apart from possibility of loss of viability, the chemicals maybe expensive to purchase.
Rudimentary embryo:
Is resulted when non-germination is caused by shedding of seed before they are morphologically mature. It requires after ripening for the seeds to mature and germinate.
Chemical inhibition:
In some cases the embryo is prevented from developing further by the presence of substances which inhibit metabolism. Such chemicals are called germinating inhibitors e.g HCN, ethylene e.t.c Such chemicals maybe present in testa, pericarp, endosperm of a seed or on the embryo itself. The mechanism of inhibition is by blocking the activity of the enzyme necessary for starch and protein breakdown. Chemical inhibitor can be removed by soaking the seeds in water, or other chemicals.
Advantages of seed dormancy
Seed dormancy allows a plant to survive seasonal hazardous conditions. It prevents germination of seed until when planted. It also prolongs viability of seed in the storage.
Disadvantages of seed dormancy
Dormancy prevents prompt germination and uniform emergence of seedlings. It contributes to volunteering of crops which becomes a weed in another year. It contributes to the longetivity of weed seeds and it also interferes with planting schedule.
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