Inheritance of Partial Resistance to White Mold in Inbred Populations of Dry Bean

Abstract

Improving partial resistance to the fungus Sclerotinia sclerotiorum (Lib.) de Bary, the causal organism of white mold disease, is a major goal of many dry bean (Phaseolus vulgaris L.) breeding programs. Our objective was to determine if selection for partial physiological resistance (PPR) or partial field resistance (PFR) among inbred lines would have potential for increasing resistance in dry bean. Three populations of F2:4 lines that originated from two hybridizations of snap and pinto bean, NY 5262 ✕ ‘Topaz’ and NY 5262 ✕ CO81‐12034, and one between navy bean, ‘Bunsi’ ✕ D76125, were tested across two greenhouse and field environments for inheritance of PPR and PFR, respectively, to white mold disease. Each population consisted of ⊄50 F2:4 lines. The PPR trait was indicated by lesion length (LL) measured on inoculated excised stems obtained from 28‐d‐old plants (28‐d assay), and PFR was evaluated in field trials with a disease incidence index (DII). Means for LL and DII, combined across 28‐d assays and field environments, were normally distributed (P > 0.01), indicating that no discrete segregation classes occurred. Transgressive segregation was observed for both LL and DII for each population. Estimates of genetic variance (σ2g) for LL in two populations and DII in each population were significant (>2 SE). Heritability estimates for LL (0.27, 0.38, and 0.66) were lower than DII (0.77, 0.58, and 0.70) for each population. Low genetic correlations between LL and DII (0.37**, 0.16, and 0.05) for each population suggested that selection for both traits is warranted. The significant estimate for σ2g, and high estimates for heritability and expected genetic gain for reduced LL and DII, indicated that progress from selection among inbred lines of dry bean for improved partial resistance to white mold could be made.