Sequential temperature control of multi-phasic dormancy release and germination of Paeonia corsica seeds

The physiological responses during dormancy removal and multi-phasic germination were investigated in seeds of Paeonia corsica (Paeoniaceae). Seeds of P. corsica were incubated in the light at a range of temperatures (10-25 and 25/10A degrees C), without any pre-treatment, after W (3 months at 25A degrees C), C (3 months at 5A degrees C) and W + C (3 months at 25A degrees C followed by 3 months at 5A degrees C) stratification, and a GA(3) treatment (250 mg center dot l(-1) in the germination substrate). Embryo growth, time from testa to endosperm rupture and radicle emergence were assessed as separate phases. Epicotyl-plumule emergence was evaluated incubating the germinated seeds at 15A degrees C for 2 weeks, at 5 and 25A degrees C for 2 months on agar water before transplanting to the soil substrate at 10, 15 and 20A degrees C and at 15A degrees C for 2 months on the surface agar water with GA(3). Embryo growth, testa rupture, endosperm rupture (radicle emergence) and growth of the epicotyl were identified as four sequential steps in seeds of P. corsica. Gibberellic acid alone and warm stratification followed by 15A degrees C promoted embryo growth and subsequent seed germination. Cold stratification induced secondary dormancy, even when applied after warm stratification. After radicle emergence, epicotyl-plumule emergence was delayed for ca. 3 months. Mean time of epicotyl-plumule emergence was positively affected by cold stratification (2 months at 5A degrees C) and GA(3). P. corsica seeds exhibited differential temperature sensitivity for the four sequential steps in the removal of dormancy and germination processes that resulted in the precise and optimal timing of seedling emergence.