Non-deep simple epicotyl morphophysiological dormancy in seeds of Helleborus thibetanus (Ranunculaceae)

Abstract

Helleborus thibetanus is a perennial herbaceous plant with high potential for medicinal and landscaping purposes. However, the dormancy characteristics of seeds and the conditions that help this species break dormancy have not been investigated. This study investigated embryo growth and the emergence of radicles and epicotyls in seeds over a range of GA₃ pretreatment and temperature sequences. Upon reaching maturity, the seeds had underdeveloped embryos that developed fully at 15 °C warm stratification within 6 weeks. Immediately after embryo growth, radicles emerged during warm stratification. However, the epicotyls failed to emerge soon after the radicle emergence. Epicotyl emergence was observed in over > 13 % of seeds with an emerged radicle following 4 weeks of cold stratification at 4 °C. The effects of GA₃ on radicle and epicotyl emergence were used to determine the specific types of seed dormancy. GA₃ pretreatment partially substituted 15 °C warm stratification to promote radicle emergence and effectively served as a substitute for the 4 °C cold stratification to break the epicotyl dormancy. The overall temperature and GA₃ requirements for breaking dormancy and seed germination indicate non-deep simple epicotyl morphophysiological dormancy in H. thibetanus.