Changes in dormancy over time

Seeds can go in and out of dormancy at different stages of their existence. Primary dormancy can be found in seeds dispersed directly from the mother plant. It develops as a result of an interaction between the genotype of the seed and the environmental conditions surrounding it.

Seeds arriving at a genebank with primary dormancy can mature in the drying room, so they are no longer dormant by the time they are packed and stored. By contrast, seeds arriving at a genebank in a non-dormant state may move into a dormant state under the conditions in the genebank. For example, a seed that is viable, but not given enough water to allow imbibition, may develop a type of induced dormancy known as secondary dormancy. This brings advantages in the wild, since it can protect a seed from germinating during a drought.

The reverse can also happen. Seeds in a dormant state may transition into non-dormancy in a process called after-ripening. Some seeds in the population gradually become more responsive to conditions that promote germination, and less responsive to conditions that restrict it. Rice and wild oats are examples of seeds that after-ripen in warm, dry conditions – in the video, you saw rice being given an after-ripening treatment by warming it in the oven.

As a result of the release of primary dormancy and the induction of secondary dormancy, it is quite possible for a seed lot that has been in storage for some time to contain seeds at different stages along the continuum of levels of dormancy. This is why, when studying dormancy, it is a good idea to use fresh seeds.