The 2012 ASHS Annual Conference

The Ranunculaceae is a family reported to have morphological dormancy (MD) or morphophysiological dormancy (MPD), with rudimentary or linear embryos. Thalictrum rochebrunianum is a perennial plant within the Ranunculaceae family. There are few reports on embryo growth, morphology, and germination in Thalictrum (Ranunculaceae) species. 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 seeds. Ripe seeds (achenes) were collected in late September. To determine the temperature requirements for embryo growth and germination in the field, the seeds were sown to the field soil. Every 2 weeks, seeds were exhumed, and phenology of embryo growth and germination was studied. Temperature requirements for embryo growth and germination were also determined by incubating seeds under controlled laboratory conditions. Additionally, the effect of GA₃ on dormancy break was tested to characterize the type of seed dormancy. Seeds had underdeveloped embryos that were about 0.5 mm, which was about 22% of those of fully matured seed. Since embryos in seeds of this species had to grow to critical length (1.5–2.2 mm) before germination was possible, seeds seemed to have morphological dormancy. When tested at the time of dispersal, no fresh seed germinated after 4 weeks of incubation at 20 °C. Therefore, the seed dormancy type for T. rochebrunianum seemed to be morphological and physiological, i.e. morphophysiological. In natural conditions, embryo growth and germination occurred in early March 2012 and late March 2012, respectively. In laboratory experiments, after 4–8 weeks of cold stratification at 1 or 5 °C embryos grew rapidly during incubation at 25/15 °C (warm temperature). It seemed that embryo dormancy was broken by cold stratification when stored for more than 4 weeks, and then the embryos started to grow by warm temperature. GA₃ substituted for cold stratification to break dormancy in seeds of T. rochebrunianum. After 1,000 mg·L^-1 GA₃ treatment, 86.7% of the seeds germinated after 3 weeks of incubation at 25/15 °C. Consequently, seeds of T. rochebrunianum can be characterized as having non-deep simple morphophysiological dormancy.