SEASONAL-CHANGES IN GERMINATION RESPONSE OF BURIED SEEDS OF OROBANCHECRENATA FORSK

Orobanche crenata seeds, collected in Syria, Egypt and Spain, were bur ied in the field in Syria (all three seed lots) and Spain (only Spanis h seeds) and at regular intervals exhumed and tested for germination, to investigate whether the seeds exhibit an annual dormancy/non-dorman cy cycle. When exposed directly to the synthetic germination stimulant GR24 for 7 days at 20 degrees C, seeds only germinated in autumn afte r the first rains and to a limited extent in winter. When the seeds we re conditioned for 11 days at 20 degrees C prior to exposure to GR24, germination occurred during summer and autumn, but seeds were dormant in winter and early spring. The observed seasonal pattern in germinabi lity, in relation to rainfall and soil temperature, was largely consis tent with the results of an in vitro experiment by Van Hezewijk et al. (1993), investigating the effect of conditioning temperature and cond itioning period on germination capacity and the development of seconda ry dormancy. Moisture and temperature can therefore be considered the major factors regulating induction and alleviation of dormancy in buri ed O. crenata seeds. There were no basic differences in response owing to site of collection of O. crenata seeds, nor to the location where they were buried.