White mold, caused by Sclerotinia sclerotiorum (Lib.) De Bary, is a serious yield reducing fungal pathogen of common bean (Phaseolus vulgaris L.). The objective of this study was to: identify QTL for resistance to white mold and associated agronomic traits in two inbred backcross line (IBL) populations derived from the recurrent black bean parent Tacana; two recombinant inbred line (RIL) pinto bean populations derived from a common parent AN-37 and to explore the role of defense genes during infection of bean genotypes with contrasting responses to white mold. In the IBL populations selective phenotyping failed to detect QTL for field disease resistance but other agronomic traits less sensitive to environmental conditions were detected. Four novel QTLs for white mold resistance were identified in the greenhouse straw test on bean chromosomes Pv03, Pv07, Pv09 and Pv11, respectively and two previously mapped QTL were also validated on Pv02 and Pv04. The two pinto bean RIL populations were genotyped with SSR, InDel and SNP markers resulting in two linkage maps of 1183 and 953 cM and a total of fifty QTL were identified in different years for eight traits (white mold disease incidence, seed yield, days to flowering, days to maturity, 100 seed weight, canopy height, lodging and the straw test). These QTL were located across all 11 chromosomes with LOD scores ranged from the threshold of 2.5 to 10.5. Six new QTL for yield were identified on Pv01, Pv02, Pv03, Pv05 and Pv09. Seven new QTL for white mold were identified on Pv01, Pv04, Pv07 and Pv08 and two were validated on Pv02 and Pv03.Analysis of defense genes in response to white mold infection showed variable temporal transcription suggesting that the resistance reported in different bean genotypes to white mold could be due to different defense pathways. The induction of defense genes at different time points in the contrasting genotypes confirm the quantitative nature of the observed resistance to white mold in common bean.
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