Photoperiod-insensitive Japanese soybean landraces differ at two maturity loci

Insensitivity of flowering to long daylengths is an important character in the adaptation of soybean [Glycine mar (L.) Merrill] to higher latitudinal environments. The objective of this study was to identify and map the maturity genes for incandescent long daylength (ILD) insensitivity for two landraces, 'Miharudaizu' and 'Sakamotowase', which belong to different cultivar groups. Two F-9 recombinant inbred line (RIL) families were developed by means of a repetitive heterozygote selection method from the F-2 population of the cross between the two landraces. Linkage analyses with isozyme and simple sequence repeat (SSR) markers revealed that the maturity gene for ILD insensitivity from Miharudaizu was a recessive allele at the E4 locus on Molecular linkage group (MLG) I. The MLG I order of the E4 locus and four markers was determined as Satt239-Satt496-E4-Enp-Satt354. The maturity gene for ILD insensitivity from Sakamotowase was found to cosegregate with four tightly linked SSRs on MLG C2, and was determined as a recessive allele at the El locus. The genotypes at the E3 locus for both Miharudaizu and Sakamotowase were estimated as e3e3 on the basis of the responses of late-flowering near-isogenic lines to fluorescent long daylength (FLD). The results obtained in this study suggest that Miharudaizu has the genotype of E1E1e3e3e4e4 and Sakamotowase has the genotype of e1e1e3e3E4E4. Because the e1 allele cannot induce flowering in ILD in the presence of the E4 allele, an unknown gene may condition the ILD insensitivity of Sakamotowase, possibly while combined with the e1 allele.