PHYSIOLOGICAL ASPECTS OF SEED DORMANCY IN WOODY ORNAMENTAL PLANTS

Characterization of seed dormancy in woody ornamental species is a major problem since it is a relative phenomenon. At harvest, seeds are generally regarded as dormant when they germinate slowly, produce abnormal seedlings, and are unable to germinate in apparently favourable condition. In particular, they are unable to germinate within a wide range of temperatures. They often present a physiological dormancy associated with a seed-coat imposed dormancy. Breaking of dormancy corresponds to a widening of the temperature range within which germination is possible. Cold treatment for at least 4 weeks generally can eliminate this dormancy, but various other treatments (anoxia, GA, KCN) can lead to the same result. Studies performed with Pyrus malus and Fagus sylvatica demonstrate that ABA and GA are involved in the regulation of such a dormancy, but ethylene can also play a crucial role.