Mapping QTL affecting the vertical distribution and seed set of soybean [Glycine max (L.) Merr.] pods

Number of pods per plant and number of seeds per pod are quantitative, multigenic traits and important components of yield in soybean [Glycine max (L.) Merr.]. Pods are distributed unevenly in the upper, middle, and lower segments of the plant and this distribution is affected by sowing date (SD). A population of four-way recombinant inbred lines (FW-RIL), containing 160 F2:8 individuals, was generated from the cross (Kenfeng 14 × Kenfeng 15) × (Heinong 48 × Kenfeng 19). A linkage map consisting of 275 simple sequence repeat (SSR) markers was used to map quantitative trait loci (QTL) associated with the production of one, two, three, and four seeds per pod in the upper, middle, and lower segments of plants at two SDs, totaling 12 measurements per SD. A wide range of variation in the twelve characteristics was observed among the four parental lines and the FW-RIL population at the two SDs. The effect of SD2 (May 17, 2016) on pod number was stronger than that of SD1 (May 7, 2016) because the heritability of each trait in the SD1 experiment was generally greater than that of SD2. The study identified 76 QTL controlling pod number, with the phenotypic variation explained by each QTL ranging from 1.86% to 13.71%. The numbers of QTL controlling one, two, three, and four seeds per pod were 28, 23, 23, and 23, respectively. There were 30, 28, and 28 QTL controlling the pod number in the upper, middle, and lower segments of the plant, respectively. Forty-five QTL were identified at SD1 and 38 QTL were identified at SD2. Seventeen QTL were associated with pod-number traits. The QTL qPN-A1–3 was associated with the number of pods containing one seed in the middle segment of the plant at both SDs. Sixty-three QTL were published QTL (common areas existed when integrating on a map GmComposite2003 of Wm82 based on left and right markers). and 13 QTL related to pod number were newly discovered. These results provide a reference for breeders to improve soybean yield by combining advantageous alleles for these QTL. Future studies may reveal candidate genes for these QTL and identify causal alleles for marker-assisted selection. Keywords: Soybean, Pod number, QTL, Sowing date, Vertical distribution