Effects of gamma-ray irradiation on interspecific hybridization between Chamaecyparis obtusa S. et Z. and Chamaecyparis pisifera S. et Z

C. obtusa S. et Z. is one of the most important forest trees in Japan, and possesses high wood quality. It adapts to dry or semi-dry planting sites, but when it is planted in humid and productive soil, physiological damage is often seen, and its woods are not resistant against termite harm. On the contrary, C. pisifera S. et Z. has high adaptability to humid and productive soil, and is resistant against termite harm. In order to improve the resistance of C. obtusa against diseases and insects, an attempt to obtain a hybrid between C. obtusa and C. pisifera has been made. However, it was found to be very difficult to obtain the hybrid because of low cross compatibility. Therefore, the radiosensitivity of reproductive organs and the induction of mutation in C. obtusa and C. pisifera, the cause of interspecific incompatibility between both species, and the possibility of breaking down the incompatibility were investigated. Also, the cytological screening of the hybrids between C. obtusa and C. pisifera was made. It was considered that the acute gamma-ray irradiation from 500 to 600 R on male flowers was optimum for the hybridization of the present purpose. All of the hybrids produced in this study were triploid. (Kako, I.)