TEMPERATURE REQUIREMENTS DIFFER FOR THE TWO STAGES OF SEED DORMANCY BREAK IN AEGOPODIUM PODAGRARIA (APIACEAE), A SPECIES WITH DEEP COMPLEX MORPHOPHYSIOLOGICAL DORMANCY

Only a few Studies have considered the possibility that low temperature requirements may vary among stages of dormancy break in seeds with morphophysiological dormancy (MPD). We show that this lack of consideration in previous Studies on seed dormancy and germination of Aegopodium podagraria might explain the low germination percentages and/or the relatively long periods of incubation needed for germination. Under natural temperatures, embryos began to grow in September and were fully elongated by late December; most growth occurred when the average daily mean temperature was about 10 degrees C. Radicles emerged Under snow in late winter. and cotyledons emerged after snowmelt in early spring. In laboratory experiments, 100% of the embryos grew to full length at both 0 and 5 degrees C. whereas 0 degrees C was much more effective than 5 degrees C in overcoming the physiological dormancy in seeds after embryos were fully elongated. Following radicle emergence, cotyledons emerged readily in a wide range of temperatures >= 5 degrees C. GA(3) did not substitute for the low temperature requirement for dormancy break. Seed dormancy in A. podagraria fits Nikolaeva's formula for deep complex MPD. i.e., C3B-C-3. Better germination of seeds pretreated at 0 degrees than at 5 degrees C has practical implications for cultivating this species.