PHOTOPERIOD SENSITIVITY GENE OF SE-1 LOCUS FOUND IN PHOTOPERIOD INSENSITIVE RICE CULTIVARS OF THE NORTHERN LIMIT REGION OF RICE CULTIVATION

Heading trait mainly determined by photoperiod sensitivity and basic v egetative growth greatly contributes to the climatic and regional adap tability of rice (Oryza sativa L.) cultivars. In Hokkaido of Japan (42 -45 degrees N), the northern limit region of rice cultivation, extreme ly early maturing (heading) cultivars with photoperiod insensitivity a re planted. In the present study, the gene analyses of 12 Hokkaido cul tivars 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 unexpected ly showed that eight of 12 cultivars examined carried a photoperiod in sensitivity gene Se-1(e) and four of them carried a photoperiod sensit ivity gene Se-1(n). Unlike a photoperiod insensitivity gene e(1) that most of the Hokkaido cultivars carry at the E-1 locus, Se-1(e) was con sidered not to be necessarily required in realizing the photoperiod in sensitivity of Hokkaido cultivars. It was also suggested that some gen etic factor(s) suppressing the expression of Se-1(n) is present among Hokkaido cultivars. This factor was considered to take part in establi shing Hokkaido cultivars together with e(1). Further analysis on ident ifying this factor will be required for the efficient breeding of rice adapting to the northern limit region of rice cultivation.