QTL Mapping and integration as well as candidate gene prediction for branch number in soybean

Branch number is an important factor that affects crop plant architecture and yield in soybean. With the aim of elucidating the genetic basis of branch number, we identified 10 consensus quantitative trait loci (QTLs) through preliminary mapping, which were on chromosome A1, B2, C1, C2, D1a, D1b, F, L and N, explained 0.3-33.3% of the phenotypic variance. Of these, three QTLs were identical to previously identified ones, whereas the other seven were novel. In addition, one major QTL-qBN.C2 (R2=33.3%) was detected in all three environments and another new major QTL-qBN.N (R2=19.6%) was detected in two environments (Taiyuan 2017 and Taiyuan 2018), but only in Taiyuan. Thus, the QTL x environment interaction analysis confirmed that QTL-qBN.N was strongly affected by the environment. We compared the physical positions of the QTL intervals of the candidate genes potentially involved in branching development, and five orthologous genes were ultimately selected and related to the establishment of axillae meristem organization and lateral organs, qBN.A1 (SoyZH13_05G177000.m1), qBN.C2 (SoyZH13_06G176500.m1, SoyZH13_06G185600.m1), and qBN.D1b-1 (SoyZH13_02G035400.m1, SoyZH13_02G070000.m3). The results of our study reveal a complex and relatively complete genetic architecture and can serve as a basis for the positional gene cloning of branch number in soybean.