Identification of Quantitative Trait Loci Conditioning Resistance to Fusarium Root Rot in Common Bean

Abstract

Fusarium root rot [caused by the soil borne pathogenFusarium solani(Mart.) Appel & Wr. f. sp.phaseoli(Burk.) Snyd. & Hans.] is a major constraint to common bean (Phaseolus vulgarisL.) production worldwide. The objectives of this study were to transfer Fusarium root rot resistance from small‐seeded Middle American black bean into highly susceptible large‐seeded Andean kidney and cranberry bean genotypes and identify quantitative trait loci (QTL) associated with Fusarium root rot resistance in common bean. Two inbred backcross line (IBL) populations, developed from crosses between small‐seeded resistant and large‐seeded genotypes, were evaluated for reaction to root rot during 2 yr in field and greenhouse experiments. Significant genetic variation that displayed continuous transgressive segregation toward root rot susceptibility confirmed the quantitative nature of resistance. Highly significant treatment‐by‐environmental effects were observed. Narrow‐sense heritabilityh2Nestimates for resistance ranged from 0.10 to 0.51 for the kidney and from 0.20 to 0.82 for the cranberry IBL populations. Nine QTL significantly associated with Fusarium root rot resistance in the field and greenhouse, explained from 5 to 53% of the total phenotypic variability. The QTL associated with root rot resistance were located on linkage groups (LGs) B2 and B5 of the integrated bean map close to previously identified QTL for resistance on B2. On the basis of a linear regression model, a combination of five markers associated with QTL on two different LGs accounted for 73% of the phenotypic variation for root rot resistance. Data from the current study provides breeders the opportunity to combine, through marker‐assisted backcrossing, large‐effect QTL identified on different LGs to enhance root rot resistance in Andean germplasm of common bean.