Dormancy breaking and germination requirements of seeds of Thalictrum uchiyamae (Ranunculaceae) with underdeveloped embryos

Thalictrum uchiyamae Nakai is an herbaceous perennial plant that has potential for greater utilization for landscaping and medicinal purposes. In the present study, we investigated some of the factors that affect seed dormancy and germination in this species. To determine the temperature requirements for embryo growth and germination in field conditions, the seeds were buried in field soil. Every 1 or 2 weeks, the seeds were exhumed, and embryo growth, germination, and seedling emergence were investigated. In the laboratory, the effects of temperature and GA(3) on dormancy break and germination were investigated in order to characterize the seed dormancy. The seeds had underdeveloped embryos that were physiologically dormant at maturity in late September. In natural conditions, embryo growth and germination occurred in March of the following year, and seedlings emerged in early April. The physiological dormancy of the embryos was broken by cold stratification at 5 degrees C for 8 weeks, but warm temperatures (25/15 degrees C) were required to promote embryo elongation even after the physiological dormancy was broken. GA3 treatment could substitute for the cold stratification requirements and broke seed dormancy of T. uchiyamae, 87.3% of which germinated after 8 weeks of incubation at 25/15 degrees C at 100 mg.L-1 GA(3) soaking treatment. These results suggest that the seeds of T. uchiyamae exist in a state of non deep simple morphophysiological dormancy. The temperature requirements for the dormancy break of the seeds enabled the seedlings to emerge in the very beginning of the growing season the following year. These results represent practical knowledge for propagation of these plants from seed.