Interactive effects of two heading-time loci, Se1 and Ef1, on pre-flowering developmental phases in rice (Oryza sativa L.)

The interaction between the Se1 and the Ef1 loci, which chiefly control the photoperiod sensitivity (PS) and the basic vegetative growth (BVG) period of rice (Oryza sativa L.) respectively, was investigated using four tester lines different in genotype for the two heading time loci from each other. The four tester lines were grown under 10, 13, 14, 15, and 16h daylengths to estimate their BVG period and PS. The Taiwanese cultivar Taichung 65 (T65), one of the tester lines, has an extremely long BVG period that has been considered to be conferred by a late heading-time allele ef1 at the Ef1 locus. Experimental results, however, showed that the extremely long BVG of T65 was conferred not by a single effect of ef1 but by a complementary effect of ef1 and Se1-e, a photoperiod insensitivity allele, at the Se1 locus. It was also found that a complementary effect of a PS allele Se1-n at the Se1 locus and ef1 stimulates the PS of rice, Gene analysis for heading time under an optimum daylength (10 h) as well as under natural daylength confirmed the presence of the complementary effect of the two nonallelic genes on BVG, which was found only with homozygosity of both the genes. Based on these results and earlier reports on the Se1 locus, the roles of the Se1 and Ef1 loci on the durations of pre-flowering developmental phases in rice were discussed.