Flower-Bud Formation of Cryptomeria under Controlled Environment* Hiroshi MIYAJIMA and San-Keun CRON Summary In order to elucidate the correlation of temperature and the effect of gibberellin spray on the development of flower-buds in Cryptomeria japonica

In order to elucidate the correlation of temperature and the effect of gibberellin spray on the development of flower-buds in Cryptomeria japonica cultivar Kumotooshi, experiments were done in controlled environmental condition during 1970-1971. The following points were observed: 1. The male flower-buds were formed maximum in the temperature range of 25°C-30°C and their formation decreased with the decrease in temperature. On the other hand, the female flower-buds were formed maximum in the temperature range of 20°C-25°C. At 15°C the both flower-buds were hardly differentiable. At 33°C, they were differentiated, but soon they changed into leaf buds and chlorosis was observed. 2. Male and female flower-buds were formed even at temperatures lower than the optimum ones when sprayed with gibberellin. 3. The effects of the temperature treatment was most predominant at the early term (May 10-Jun. 24) of differentiation in both male and female flower-buds. 4. Under alternating temperature condition the male flower-buds were formed maximum when the mean temperature was around 30°C, and around 20°C, the female flower-buds were formed maximum. 5. Neither male nor female flower-buds were formed at constant temperature treatment (33°C) in the whole period (MaySeptember). However, with a short time treatment at 33°C, the flower-buds were formed in both cases of constant and alternating temperatures. 6. Even at 30°C, the male flower-buds were formed after the samples were treated at the low temperature (chilling) in winter. This result suggests that chilling as a pretreatment is essential for the flower-bud formation and both adequate temperature and day length conditions can control the flower-bud differe ntiation period.