Direct and Marker‐Assisted Selection for Resistance to Common Bacterial Blight in Common Bean

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ABSTRACTCommon bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans is a seed‐borne disease that can significantly reduce yield and seed quality of common bean (Phaseolus vulgaris L.). Disease resistance is the most effective management strategy, but most common bean cultivars have no CBB resistance. Marker‐assisted selection (MAS) shows promise as a method to facilitate pyramiding CBB resistance between common bean gene pools. This study compared the efficiency of direct disease resistance selection (DDS) and MAS for the pyramiding and transfer of CBB resistance into dark red kidney bean. Direct disease resistance selection and MAS were applied independently, from the F1 through the F5, in an inter‐gene pool double‐cross population, Wilkinson 2/dark red kidney (DRK) 2//DRK 1/VAX 3. Replicated trials were performed in the greenhouse and field in 2006 and 2007 to assess levels of CBB resistance in 15 breeding lines independently developed with each method. Under high disease pressure, in two greenhouse environments, 12 resistant breeding lines were obtained with DDS compared with six using MAS, and the overall CBB mean disease severity index was 3.3 for DDS and 4.2 for MAS. Under moderate disease pressure in the field, there was no significant difference (p > 0.05) between the responses of breeding lines developed by the two selection methods. The cost of DDS was US$1.55 per plant compared to $2.03 for MAS.