Anomalous germination of dormant dehulled red rice seeds provides a newperspective to study the transition from dormancy to germination and to unravel the role of the caryopsis coat in seed dormancy

Seed dormancy is the temporary inability of an imbibed seed to germinate under otherwise favourable conditions. It is an important trait for seed persistence in many higher plants. Dormant dehulled red rice caryopses can have a strong dormancy: the studied population shows an almost complete dormancy; that is, these caryopses do not germinate (usually germination is < 1-2%) when incubated in water for the time usually adopted for germination tests (i.e. 2 weeks). However, after several months of incubation in water, dormant red rice caryopses start germinating in an anomalous manner. Most notably, the piercing of the caryopsis coat is very slow, sometimes arrested, until the coat completely breaks down and embryo growth is resumed. There is, therefore, a time lag between the initial rupture of the caryopsis coat and the start of seedling growth. It is argued that embryo growth can be triggered by the failure of the caryopsis coat even if seed dormancy has not been previously relieved, and thus germination is started and dormancy is forcefully interrupted. Accordingly, the time course of the anomalous germination shows a Gompertz distribution of times to failure. It is concluded that: (1) if the seed rests with the coat ruptured without further growth, it is still dormant; if so, therefore, (2) the breaking of the coat is not necessarily a marker of germination in this context.