Breaking Bud Dormancy in Erythronium japonicum Decne. (Liliaceae) by Natural and Artificial Chilling

Abstract

This study was conducted to investigate flower bud differentiation and to determine the chilling requirements for bud dormancy breaking and sprouting in Erythronium japonicum Decne. (Liliaceae). The dormant bulbs grown in an open field were randomly selected from June to December, 2012 for observation of flower bud differentiation and development. The 3-4 year old bulbs and >10 year old bulbs were used for vegetative development and flower bud development, respectively. For natural chilling treatments, the plants were transferred from an experimental field to a growth module every month from September to February. Artificial chilling treatments were applied at 5°C for 0, 2, 4, 8, and 12 weeks in October and November. Modified Chilling Hours Model (MCHM) and Modified Utah Model (MUM) were used for calculating the chilling hours. Flower bud initiation and differentiation in E. japonicum were observed in May, and from June to July, respectively, followed by the flower bud elongation after August. Sprouting and bud break did not occur throughout the experiment when dormant bulbs were transferred from September (0 MCH and 0 MCU) to November (612 MCH and 839.5 MCU). However, all plants sprouted when the dormant bulbs were transferred after January (1,956 MCH and 1,914.7 MCU). Prolonged cold storage also promoted sprouting of dormant E. japonicum. No or 4 weeks (672 MCH and 684 MCU) of cold storage at 5°C in October did not induce bud break and sprouting. However, when the dormant bulbs were stored at 5°C for 12 weeks (2,016 MCH and 2,030 MCU) in October, percent sprouting increased to 72.7%. The chilling treatment for 8 weeks (1,571 MCH and 1,886 MCU) or 12 weeks (2,243 MCH and 2,558 MCU) at 5°C in November resulted in 72.7% and 100% of sprouting. In conclusion, at least 1,956 MCH or 1,914 MCU in natural chilling and 1,571 MCH or 1,886 MCU of cold storage could be recommended for dormancy breaking in forcing culture of E. japonicum.