Late flowering in F 1 hybrid rice brought about by the complementary effect of quantitative trait loci

Late flowering sometimes occurs in F 1 hybrids between rice varieties ( Oryza sativa L.), although the parental varieties show similar days-to-flowering (DTF). The genetic architecture prompting the occurrence of such late flowering is poorly understood. To clarify the genetic architecture of late flowering in F 1 hybrids from a cross between rice varieties, ‘Koshihikari’ and ‘IR64’, we performed quantitative trait locus (QTL) analysis using an F 2 population (selfed progeny of an F 1 plant), in which heterozygous genotypes should segregate in a certain proportion in a Mendelian manner. The QTL analysis detected three significant QTLs. At one QTL (putatively Heading date 1 ), the ‘Koshihikari’ allele increased DTF, and at the other two QTLs (putatively Heading date 6 and Oryza sativa Pseudo - Response Regulator 37 / Heading date 2 ), the ‘IR64’ alleles increased DTF. All alleles at these three QTLs showed partial dominance. The combination of the QTLs explained 82.2% of the total phenotypic variance of DTF in the F 2 population, with contribution from epistasis between QTLs. There was no difference between DTFs of F 1 hybrids and heterozygous genotypes for the three QTLs. Our results demonstrated that the complementary effects accompanied by epistasis of at least three QTLs were responsible for late flowering in F 1 hybrids.