Non-deep simple morphophysiological dormancy in seeds of Thalictrum rochebrunianum, an endemic perennial herb in the Korean Peninsula

Abstract

The aims of this study were to determine the requirements for dormancy break and germination and to characterize the type of seed dormancy of T. rochebrunianum. Ripe seeds (achenes) were collected in late Sept. To determine the temperature requirements for embryo growth and germination in the field, the seeds were sown in field soil. Every 1 or 2 weeks, the seeds were exhumed, and the phenology of embryo growth, germination and seedling emergence were investigated. In the laboratory, effects of temperature and GA3 treatment on embryo growth and germination were also investigated to characterize the type of seed dormancy. Seeds had underdeveloped embryos, which were about 20% of the size of those in fully matured seeds. In natural conditions, embryo growth and germination occurred in early and late March next year, respectively, and embryos in the seeds of this species had to grow to a critical length before germination was possible. Thus, the seeds had morphological dormancy (MD). When tested at the time of dispersal, few seeds germinated after 4 weeks of incubation at 25/15°C. Therefore, the seed dormancy type for T. rochebrunianum seemed to be morphophysiological. Embryos in the seeds grew rapidly at warm temperature conditions following cold stratification at low temperatures. After 4–12 weeks of cold stratification at 1°C or 5°C, the seeds germinated rapidly during an incubation at 25/15°C. Cold stratification requirements could be substituted by GA3 treatment in seeds of T. rochebrunianum. After 1000 mg·L-1 GA3 treatment, high percentages (≥ 80%) of the seeds germinated after 4 weeks of incubation at 15/6, 20/10, and 25/15°C. Consequently, seeds of T. rochebrunianum could be characterized as expressing non-deep simple morphophysiological dormancy (MPD). The cold stratification requirements for dormancy break enabled the seeds to produce seedlings at the beginning of the growing season in natural conditions.