SEASONAL-CHANGES IN GERMINATION RESPONSES OF BURIED SEEDS OF THE WEEDY SUMMER ANNUAL GRASS SETARIA-GLAUCA

Seeds of Setaria glauca (L.) Beauv. buried in soil and exposed to natu ral temperature cycles exhibited seasonal changes in temperature, but generally not light:dark requirements for germination. Seeds were dorm ant at maturity in late September and October (autumn), and during bur ial from October to January they entered conditional dormancy, germina ting up to greater than or equal to 60% in light and darkness at daily thermoperiods of 25/15, 30/15 and 35/20 degrees C by January. During burial from February to May or June, seeds became non-dormant and germ inated up to 68-100% in light and darkness at 15/6, 20/10, 25/15, 30/1 5 and 35/20 degrees C in May or June. At maximum yearly temperatures i n June or July-August, 65-89% of the seeds entered conditional dormanc y (germinating at 30/15 and 35/20, but not at 15/6, 20/10 and 25/15 de grees C), and the others entered dormancy (not germinating at any ther moperiod). Thus, most buried seeds had an annual conditional dormancy/ non-dormancy cycle, but some had an annual dormancy/non-dormancy cycle . Except for seeds buried in 1990 that lost the ability to germinate i n darkness at all thermoperiods the first summer of burial, seeds incu bated in light and in darkness exhibited the same patterns of seasonal changes in germination responses. Although conditionally dormant and non-dormant seeds germinated to high percentages in darkness in Petri dishes, seedlings were found only in bags of seeds exhumed in April an d May 1983, indicating that some factor(s) associated with the burial environment other than darkness prevented germination of buried seeds.