Dormancy | Agriculture Optional Notes for UPSC PDF Download

Dormancy

The second reason seeds resist germination is dormancy. Dormancy is when the seeds do not germinate, even though conditions for germination are favorable. Something about the seed prevents germination.
Barriers to germination could include:

• Barriers in the protective covering:
  • A seed coat, or pericarp, that is impermeable to water or oxygen.
  • Compounds that act as germination inhibitors that are embedded within the seed coat.
• Barriers in the embryo:
  • Physiological immaturity of embryo: the embryo is initially immature and requires a period of cool temperatures or alternating warm and cool temperatures to fully mature.
  • Endodormancy in temperate plants: internal biochemical processes must be met in the seed before germination can begin. Endo-dormancy is the first stage of dormancy for many seeds from plants grown in temperate environments like Minnesota. Once the internal biochemical processes are met, the seed usually goes into eco-dormancy.
  • Ecodormancy: external factors are not optimal for germination. This is often due to temperatures being too cold, or to amounts of water not sufficient for germination.

The ways in which horticulturists overcome seed dormancy depend on the type of dormancy. For seeds with impermeable seed coat, such as the Kentucky coffeetree (Gymnocladus dioicus) seen above, a technique called scarification is used. Sandpaper is used to break through the seed coat until the white cotyledon is visible. Under warm, moist conditions, these seeds will germinate. To germinate a large amount of seed, there are other ways to break the seed coat, such as using acid to “etch” holes in the seed coat to allow for water imbibition.

In the case of endodormancy, we usually have to be patient. Seeds are placed in a cool (38–42ºF) place under moist conditions. This process is called stratification. Depending on the plant species, stratification can take from 2 weeks to almost a year. It is as easy as putting seeds in a sealable plastic container or bag with moist media, and placing them into a refrigerator.

Dormancy is a great strategy for enhancing a plant’s survival potential because germination is delayed until a later time when environmental conditions are more favorable. However, for horticulturists who prefer that a seed germinate as quickly as possible after being planted, dormancy is a nuisance. One of a horticulturist’s important skills is to recognize dormancy, identify the dormancy mechanism, and take steps to overcome the inhibition so that plants can grow predictably from seed when planted.