Genetic analysis of reproductive traits in soybean [Glycine max (L) Merr]
The objectives of this study were to: (1) estimate the number of genes controlling photoperiod insensitivity in soybean; (2) map quantitative trait loci controlling flowering time, maturity, and photoperiod insensitivity in soybean; (3) map homologous and cloned flowering time gene sequences in soybean; (4) correlate these sequences with maturity (E) loci by means of near isogenic lines (NILs). Three populations, two F 6:7 recombinant inbred lines of 101 and 100 progeny and an F2:4 G. max x G. soja population (60 progeny), were used. Forty-one NILs were also included. At least three genes were proposed to control photoperiod insensitivity in soybean. A large-effect QTL for days to R1, R3, R7, and photoperiod insensitivity was found at the same location on linkage group (LG) C2 in both populations. This QTL explained as much as 47% of total phenotypic variance. This result suggests that photoperiod insensitivity, flowering time, and maturity may be controlled by the same gene(s) or by tightly clustered genes in the same chromosomal region. Minor QTL were also detected controlling the four traits in both populations. Minor QTL account for as much as 17.8% of phenotypic variance. Thus, time of flowering, maturity, and photoperiod insensitivity in these soybean populations are proposed to be controlled by a major QTL with a large effect and modified by several minor QTL. Ten of the 18 homologous and cloned flowering time gene sequences have been mapped. The gene sequences were mapped onto LGs A2 (CRY2 ), B1 and H (COL1), A1 and B2 (PHYA), C1 (DET1 and LD), D2 (AP2), E and K (PHYB), F (COL2), L (FCA ), and Q (CCA1). None of these cDNA sequences have been found to be directly associated with previously mapped QTL for flowering time. However, analyses of these candidate genes using NILs show that the FCA homolog was associated with maturity locus E3. The map positions and phenotypic data support that homologous gene sequence FCA is a strong candidate for maturity locus E3. Analyses of NILs suggest that PHYB homolog may be associated with maturity locus E1. However, current data show E1 and PHYB mapped in different LGs.