Phytochrome Controlled Changes in Dormancy and Germination of Buried Weed Seeds

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Seeds of six weed species were buried in the field at depths of 2.5, 7.6, and 15.2 cm. Seed germination after various light and temperature treatments was determined before burial and after recoveries in darkness at 3-month intervals over 12 and 20-month periods. In one experiment the five species studied were ungerminable before burial. After 6 months burial, most species responded to light but became ungerminable again after this time. These results suggest cycles of dormancy where seeds pass from total dormancy at maturation to a phytochrome-controlled dormancy after burial and then return to total dormancy. During the phytochrome-controlled dormancy period, some species were highly light sensitive. In another experiment the response of yellow rocket(Barbarea vulgarisR. Br.) seeds to thirteen light and temperature treatments was determined before and after burial. Without light treatment, germination of the recovered seeds at various temperatures was low. Germination was usually high after brief exposures to red light, particularly in seeds recovered from 15.2 cm. Very large increases in germination were induced by light exposures of 3 × 10−9Einsteins cm−2incident in the 600 to 680-nm region (1 sec). The evidence suggests changes in total phytochrome (Ptot) are responsible for a seasonal change in light sensitivity and a previously undescribed type of dormancy.