Abstract
This study was conducted to elucidate the mode of inheritance of the occurrence of white-back and basal-white kernels associated with high temperature during the ripening period in rice. F1 to F3 generations from a cross between “Chiyonishiki”, which is sensitive to high temperature with a high incidence of the two types of such defective kernels, and “Koshijiwase”, which is resistant to high temperature with a low incidence of defects, were used as materials. The plants were exposed to high temperatures in a greenhouse during the period from heading to maturity. The number of heat-damaged kernels was counted to obtain the incidence rates of white-back and basal-white kernels for each plant. The incidence rates revealed differences in the model of inheritance between the two types of defective kernels, for example, low-incidence was dominant over high-incidence for the incidence of white-back kernels, while no dominance was found between low and high incidence for basal-white kernels. The values of heritability in a narrow sense for the incidence of white-back kernels and basal-white kernels were 0.350 and 0.259, respectively, in the F2 generation. The values of heritability in a true sense for the incidence of white-back kernels and basal-white kernels were 0.536 and 0.411, respectively. Selection in later generations is recommended for the breeding of a variety with a low incidence of defective kernels even at high temperatures. Moreover, the incidence of white-back kernels showed a positive genetic correlation with that of basal-white kernels. Therefore the incidence of both types of defective kernels could be reduced concurrently. The incidence of white-back kernels failed to show a significant correlation with the thousand kernel weight, kernel length and dorsiventral diameter while that of basal-white kernels showed a negative genetic correlation with the kernel length and dorsiventral diameter. These results indicate that selection for reducing the deterioration of the grain quality and the weight decrease at high temperatures during the ripening period could be achieved.
