Analysis of tester lines for rice (Oryza sativa L.) Heading-time genes using reciprocal photoperiodic transfer treatments

Sixteen heading-time tester lines of rice (Oryza sotiva L.) for the E1, E2, E3, Se1, Ef1 and U loci were subjected to transfer treatments from short (10 h) to long photoperiods (24 h) and vice versa at various times after sowing. Based on heading response, the 16 lines were classified into four groups, which corresponded well to the genotype at the Se1, Ef1 and E1 loci. 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 Se1 locus had an extremely large effect on PSP and large effects on BVP and PPP; Ef1 had a large effect on BVP and a considerable effect on PPP; and E1 had a considerable effect on PSP, although effects were modified by non-allelic interactions at these three loci. The effects of three other loci were almost negligible. Thus the Se1, Ef1 and E1 loci play principal roles in determining the heading time of rice, which is further diversified not only by the action of genes of other heading-time loci but also by non-allelic interactions. Based on these results, causal genetic pathways to flowering (heading) in rice are proposed.