3Branch number is an important factor that affects crop plant architecture and yield in 4 soybean. With the aim of elucidating the genetic basis of branch number, we 5 identified 10 consensus quantitative trait loci (QTLs) through preliminary mapping, 6 which were on chromosome A1, B2, C1, C2, D1a, D1b, F, L and N, explained 7 0.3-33.3% of the phenotypic variance. Of these, three QTLs were identical to 8 previously identified ones, whereas the other seven were novel. In addition, one major 9 QTL-qBN.C2 (R 2 =33.3%) was detected in all three environments and another new 10 major QTL-qBN.N (R 2 =19.6%) was detected in two environments (Taiyuan 2017 and 11 Taiyuan 2018), but only in Taiyuan. Thus, the QTL × environment interaction 12 analysis confirmed that QTL-qBN.N was strongly affected by the environment. We 13 compared the physical positions of the QTL intervals of the candidate genes 14 potentially involved in branching development, and five orthologous genes were 15 ultimately selected and related to the establishment of axillae meristem organization 16 and lateral organs, qBN.A1 (SoyZH13_05G177000.m1), qBN.C2 17 (SoyZH13_06G176500.m1, SoyZH13_06G185600.m1), and qBN.D1b-1 18 (SoyZH13_02G035400.m1, SoyZH13_02G070000.m3). The results of our study 19 reveal a complex and relatively complete genetic architecture and can serve as a basis 20 for the positional gene cloning of branch number in soybean. 21 4 1 Introduction 2 Plant architecture is an extremely important role in plant yield, which can affect 3 light distribution in the canopy and photosynthesis. Modification of crop plant 4 architecture has been used to improve plant fitness and agricultural performance, and 5 these modifications are achieved through genetics and breeding [1-3]. Branching is a 6 major factor that affects plant architecture, together with plant height, main stem, leaf, 7 pod and others [2]. The number and distribution of branches determine the canopy 8 architecture, which influences light interception as well as lodging resistance and 9 ultimately seed yield [4]. Branch number is strongly dependent on aspects related to 10 the cultural practices and growth environment [5]. 11 Branch number is also the most complex trait and is very sensitive to the 12 environmental conditions. Because the environmental effects on branch number are so 13 prominent, there have been few studies on the genetics of this trait, although varietal 14 differences in branch number have been observed in the adaptation to row spacing in 15 accordance with its modest heritability observed in most studies [6, 7]. Two dominant 16 alleles at independent loci were found to be associated with a high-branch number 17 phenotype [8] but the loci and other genetic factors that determine branch number in 18 soybean remain unknown. However, branch number is difficult to improve efficiently 19by traditional breeding methods and the genetic and especially the molecular 20 mechanism involved in branch number in soybean are poorly understood.
21Previous studies have shown that b...