Effects of Heading-time Genes on Pre-flowering Developmental Phases in Rice

Sixteen heading-time tester lines in rice (Oryza Sativa L.) for the six loci were subjected to transfer treatments from short (10-h) to long photoperiod(24-h) and vice versa at various times. Using an analytical model, we estimated seven parameters for the three pre-flowering developmental phases of each line: the basic vegetative phase (BVP), the subsequent photoperiod-sensitive phase (PSP), and the post photoperiod-sensitive phase until heading (PPP). The Sel locus was found to have an extrremely strong effect on PSP; Ef1, a slight effect on BVP and a considerable effect on PPP; and E1, a considerable effect on PSP, although their effects were modified by nonallelic interactions at these three loci. The effects of three other loci were almost negligible. Subsequently, two late-heading mutant lines HS169 and HS276 with an extremely long basic vegetative growth (BVG; days to heading under short photoperiod) period conferred by a recessive mutant gene ef1-h and a novel gene ef2, were subjected to photoperiodic transfer treatments. Both mutant genes were found to increase BVP and PPP markedly by themselves, whereas ef1 required nonallelic interaction with the Se1 locus. Based on the results, causal genetic pathways to flowering in rice and the significance of ef1-h and ef2 in recent rice breeding in the low latitudes were discussed.