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Orobanche crenata seeds, collected in Syria, Egypt and Spain, were buried in the field in Syria (all three seed lots) and Spain (only Spanish seeds) and at regular intervals exhumed and tested for germination, to investigate whether the seeds exhibit an annual dormancy/non-dormancy cycle. When exposed directly to the synthetic germination stimulant GR24 for 7 days at 20°C, seeds only germinated in autumn after the first rains and to a limited extent in winter. When the seeds were conditioned for 11 days at 20°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 germinability, in relation to rainfall and soil temperature, was largely consistent with the results of an in vitro experiment by Van Hezewijk et al. (1993), investigating the effect of conditioning temperature and conditioning period on germination capacity and the development of secondary dormancy. Moisture and temperature can therefore be considered the major factors regulating induction and alleviation of dormancy in buried 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. [ABSTRACT FROM AUTHOR]