Seed Dormancy: What is it?
Dormant seeds are seeds which remain viable (alive) though metabolically inactive and incapable of germination under the conditions normally favorable for the species. In other words, seed is supplied all that it needs to germinate, yet it doesn't. The seed is asleep, waiting for the proper conditions to awaken it.
There are many types of seed dormancy. It is a very complex and mis-understood condition of certain seed species. Not all species of seed that exhibit seed dormancy have the same dormancy mechanisms.
In this article, we will discuss the basics of seed dormancy. Later articles will go more into detail about the different types of seed dormancy and the mechanisms involved.
Why Do Seeds Display Dormancy?
Seed dormancy is a mechanism that insures the survival of the species. To "Mother Nature", dormancy is a blessing that insures the continuation of the species over time and through periods of environmental stress.
Seed dormancy aids a species' survival by delaying or retarding germination so that 'overall germination' is dispersed over time. This means that if the environmental conditions are not right during the normal germination period, a percentage of seeds will germinate at some later time when the conditions are right.
Dormancy pre-disposes the seed to respond to spacific environmental conditions that will favor seedling survival and maximize species proliferation.
Seed Dormancy Begins on the "Mother Plant"
Dormancy mechanisms are put in place by the Mother Plant to ensure that seeds will not germainate while still attached (vivipary). Domesticated species often have dormancy mechanisms bred out of them and therefore will display viviparous germination or what's commonly known as pre-harvest sprouting.
Germination inhibitors, such as Abscissic acid (ABA), or morphological changes in the seedcoat or pericarp (fruit coat), prevent germination on the Mother Plant. Maternal tissue surrounding the seed, such as the lemmas and paleas in grasses, play an important role in preventing viviparous germination.
Seed Dormancy and Physiological Maturity
The seed dries down at physiological maturity and is soon shed from the Mother Plant. The influence of the mother plant begins to diminish at physiological maturity.
With some seed species, the influence of the mother plant remains after the seed is shed. A period of time is needed to fully release the maternal control which prevents germination. This is known as the "After-ripening" period.
For more about after-ripening and other dormancy mechanisms see:
Seed Dormancy Mechanisms.