Identification of QTLs Associated with Biological Nitrogen Fixation Traits in Soybean Using a Genotyping‐by‐Sequencing Approach

Abstract

Although biological N fixation (BNF) is a key process for economic cultivation of soybean [Glycine max (L.) Merr.], the trait is often neglected in breeding programs, mainly due to difficulties in evaluating nodulation and N fixation parameters. We used a genotyping‐by‐sequencing approach to provide a dense genome‐wide marker coverage with 1448 single nucleotide polymorphisms (SNPs) distributed broadly across the chromosomes of a soybean population. The mapping population was composted of 113 F7:8 recombinant inbred lines, obtained by single‐seed descent method, derived from crossing of soybean cultivars ‘Bossier’ (high BNF capacity) and ‘Embrapa 20’ (medium BNF capacity). The traits evaluated were nodule number (NN), nodule dry weight (NDW), average NDW (ANDW; i.e., NDW/NN), and shoot dry weight (SDW). A genetic map was constructed with 1448 SNPs that generated 35 linkage groups totaling 1793 cM, thus covering ∼72% of the genome based on the consensus linkage map. The estimated heritability for NN, NDW, ANDW, and SDW was 0.41, 0.30, 0.30, and 49.11, respectively. Inclusive composite interval mapping identified two significant quantitative trait loci (QTLs) for ANDW at 67 cM on chromosome 13, with a logarithm of odds (LOD) score of 4.66. The additive effect of this locus was −0.31 mg nodule−1, and it explained 18.13% of the phenotypic variation. Another QTL was identified for SDW at 24 cM on chromosome 19 and exhibited an LOD score of 3.93. The additive effect was of 0.57 g plant−1, and it accounted for 14.93% of the phenotypic variation. Additive genetic effects contribute to the final phenotype. In the present study, Embrapa 20 was the major contributor to ANDW, and Bossier was the major contributor to SDW. The latter was previously reported using simple sequence repeat markers.