QTL Analysis of Symbiotic Nitrogen Fixation in a Black Bean Population

Dry bean (Phaseolus vulgaris L.) acquires nitrogen (N) from the atmosphere through symbiotic N fixation (SNF) but is considered a poor N fixer. Diversity for SNF within dry bean germplasm is recognized, and regions of the genome associated with SNF traits have recently been identified. In the current study a mapping population of 122 recombinant inbred lines (RILs), derived from the cross of two black bean cultivars (' Puebla 152 ' and ' Zorro ') contrasting in SNF traits, was grown in the field in East Lansing, MI, and Isabela, Puerto Rico, and in the greenhouse under N-free conditions to evaluate for yield, nodule development, biomass growth, agronomic traits, and N fixation. The RIL population was also genotyped with single-nucleotide polymorphism (SNP) markers developed through the BeanCAP to construct a genetic map spanning 972 cM and containing 430 SNPs. A total of 17 unique QTL associated with SNF traits were identified with most of them located in three large clusters on Pv01 (4), Pv06 (6), and Pv08 (6). Many of the QTL associated with %N derived from atmosphere, N harvest index, and % N in biomass were also associated with candidate genes expressed in the nodules and roots. The majority of QTL associated with genes expressed in the root or nodule were derived from Puebla 152, while QTL associated with genes with enhanced expression in stems and pods were associated with Zorro. The QTL described should serve as potential targets for improvement of SNF characteristics in commercial dry bean genotypes adapted to temperate zones.