Interactions between QTL SAP6 and SU91 on resistance to common bacterial blight in red kidney bean and pinto bean populations

Abstract

Breeding efforts to improve resistance in dry bean to common bacterial blight (CBB) have focused on applying marker assisted selection strategies. We examined the interaction between two independent QTL (quantitative trait loci), SAP6 and SU91, on the expression of resistance to CBB in a pinto bean F2 population and dark red kidney bean F2 population. The disease reaction for each F2 population was scored at several time points after inoculation. The dominant SCAR markers SAP6 and SU91 were simultaneously genotyped as codominant markers using a multiplex real-time PCR assay. For both populations, at each time point plants having genotypes of (su91 su91//SAP6 SAP6); (su91 su91//SAP6 sap6), and (su91 su91//sap6 sap6) were significantly more susceptible to CBB than plants with any of the six other possible genotypes (SU91 _//_ _). Only two examples were observed across both populations and all time points in which mean disease reactions were significantly different between any of the six (SU91 _//_ _) genotypes. No significant differences were observed between SU91 SU91 and SU91 su91 genotypes at any time point for either F2 population. Similarly, no significant differences in CBB reaction were observed among the three SAP6 genotypes for plants that had the su 91/su91 genotype. The results indicate CBB resistance in these two populations is primarily conditioned by the presence of at least a single copy of the SU91 QTL. The effects of pathogen isolate and population on discerning the influence of QTL on CBB resistance are discussed.