Seed dormancy pattern and germination preferences of the South African annual Papaver aculeatum

Seeds from two populations of Papaver aculeatum, collected in South Africa, were subjected to a series of experiments to investigate their dormancy and germination. Dormancy was weak: fresh seeds germinated to nearly 100% at 20/10 and 25/15 °C day/night if provided with light, up to 50% at 15/5, but not at all at 30/20 °C. Warm stratification increased germination, both in darkness and at 15/5 °C, but did not lead to germination at 30/20 °C. Cold stratification reduced germination and limited germination to the cooler temperatures. Alternating cold and warm stratifications showed that the species undergoes dormancy cycles. When subjected to three different artificial annual changing climates, with onset both in summer and autumn, most seed germinated in the first autumn. However, in cooler climates, some germination occurred during spring and the second autumn. The general dormancy pattern, reduction during a warm period and induction during a cold, was similar to that of Papaver rhoeas, a European species and a wide-spread weed. However, germination temperature preferences differed by P. aculeatum avoiding germination at high temperatures, having substantially weaker dormancy when fresh and having more easily reduced dormancy, compared with P. rhoeas. These differences most likely result in differing temporal pattern of germination in the field.