The physiological basis of seed dormancy in Avena fatua. IX. Characterization of two dormancy states.
The dormancy-breaking effect of several known germination promotors was studied in 9 genetically pure A. fatua lines during a period of controlled after-ripening. Changes in germination response showed at least 2 dormancy states in the caryopses of these lines. The first state was overcome by a short period of after-ripening and was insensitive to nitrate and azide, while the second state was more persistent and sensitive to nitrate and azide. Both states were sensitive to gibberellic acid and ethanol. In the most dormant lines a third ethanol insensitive dormancy state was present. The duration of both major dormancy states was related to several environmental factors influencing plant growth and seed storage. Duration was increased in caryopses produced from plants matured under low temp. (15°C) and decreased in caryopses produced from plants matured under high temp. (25°C). Duration was increased in caryopses after-ripened under low temp. (4°C) and decreased in caryopses after-ripened under high temp. (45°C). Dehulling the seeds prior to after-ripening reduced the duration of both major dormancy states. The multiple state dormancy system and its environmentally induced plasticity are discussed with reference to previous explanations of the dormancy mechanism in wild oats.