Abstract
Heading trait mainly determined by photoperiod sensitivity and basic vegetative growth greatly contributes to the climatic and regional adaptability of rice (Oryza sativa L.) cultivars. In Hokkaido of Japan (42-45°N), the northern limit region of rice cultivation, extremely early maturing (heading) cultivars with photoperiod insensitivity are planted. In the present study, the gene analyses of 12 Hokkaido cultivars for the important photoperiod sensitivity locus Se-1 were made, and the genetic factors responsible for the photoperiod insensitivity of Hokkaido cultivars were discussed. Experimental results unexpectedly showed that eight of 12 cultivars examined carried a photoperiod insensitivity gene Se-1e and four of them carried a photoperiod sensitivity gene Se-1n. Unlike a photoperiod insensitivity gene e1that most of the Hokkaido cultivars carry at the E1 locus, Se-1e was considered not to be necessarily required in realizing the photoperiod insensitivity of Hokkaido cultivars. It was also suggested that some genetic factor(s) suppressing the expression of Se-1n is present among Hokkaido cultivars. This factor was considered to take part in establishing Hokkaido cultivars together with e1. Further analysis on identifying this factor will be required for the efficient breeding of rice adapting to the northern limit region of rice cultivation.
