Soybean [Glycine max (L.) Merrill] is very sensitive to changes in photoperiod as a typical short-day plant. Photoperiodic flowering influences soybean latitudinal adaptability and yield to a considerable degree. Identifying new quantitative trait loci (QTLs) controlling flowering time is a powerful initial approach for elucidating the mechanisms underlying flowering time and adaptation to different latitudes in soybean. In this study, we developed a Recombinant Inbred Lines (RILs) population and recorded flowering time under natural long-day conditions. We also constructed a high-density genetic map by genotyping-by-sequencing and used it for QTL mapping. In total, we detected twelve QTLs, four of which are stable and named by qR1-2, qR1-4, qR1-6.1, and qR1-10, respectively. Among these four QTLs, qR1-4 and qR1-6.1 are novel. QTL mapping in two sub-populations classified by the genotype of the maturity locus E2, genetic interaction evaluation between E2 and qR1-2, and qRT-PCR indicated that E2 has an epistatic effect on qR1-2, and that causal gene of qR1-2 acts upstream of E2. We presumed the most likely candidate genes according to the resequencing data and briefly analyzed the geographic distributions of these genes. These findings will be beneficial for our understanding of the mechanisms underlying photoperiodic flowering in soybean, contribute to further investigate of E2, and provide genetic resources for molecular breeding of soybean.

大豆 [ Glycine max (L.) Merrill] 作为一种典型的短日照植物，对光周期的变化非常敏感。光周期开花在很大程度上影响大豆的纬度适应性和产量。识别控制开花时间的新数量性状基因座（QTL）是阐明大豆开花时间和适应不同纬度的机制的有力初步方法。在这项研究中，我们开发了重组自交系（RIL）群体并记录了自然长日照条件下的开花时间。我们还通过测序基因分型构建了高密度遗传图谱，并将其用于 QTL 定位。我们总共检测到了 12 个 QTL，其中 4 个是稳定的，分别命名为qR1-2、qR1-4、qR1-6.1和qR1-10。在这4个QTL中，qR1-4和qR1-6.1是新的。根据成熟位点E2基因型划分的两个亚群体的 QTL 定位、 E2与qR1-2之间的遗传相互作用评估以及 qRT-PCR 表明E2对qR1-2具有上位效应，并且qR1-的致病基因2作用于E2的上游。我们根据重测序数据推测出最有可能的候选基因，并简要分析了这些基因的地理分布。这些发现将有助于我们了解大豆光周期开花的机制，有助于E2的进一步研究，并为大豆分子育种提供遗传资源。