Mapping and comparison of quantitative trait loci for soybean branching phenotype in two locations

The number and distribution of branches in soybean plants influence seed yield through effects on the efficiency of light utilization as well as on tolerance to lodging. We have developed recombinant inbred lines (RILs) from a cross between two experimental determinant lines, which differ in branching number. The 172 RILs were divided into four maturity groups according to their alleles for two maturity loci, E1 and E3, and were planted separately to avoid confounding effects of competition. The late-maturity RIL groups with the E1 genotype were grown in two different locations, whereas the early-maturity RIL groups with the e1 genotype were planted at one location. Analysis of all lines resulted in the identification of five quantitative trait loci (QTLs) for branching number, designated qBr1 to qBr5. Among these QTLs, qBr1 and qBr2 were mapped to the proximal regions of the E1 and E3 loci, respectively. The other three QTLs were mapped to regions distant from any known maturity loci and were detected only in the presence of the E1 genotype, indicating that they interact with qBr1. Our results suggest that branching number might be controlled genetically by the identified QTLs, even though the maturity loci substantially affect branching phenotype.