Combining ability of Phaseolus vulgaris L. for resistance to common bacterial blight

Many diseases limit dry bean and snap bean yields. Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv phaseoli, is one of the most ser ious bacterial diseases in dry bean and snap bean that cause crop losses. S ince there is no satisfactory chemical control, the use of resistant cultiv ars is an important control measure, Genetic studies of resistance are impo rtant for choosing appropriate breeding methods. Combining ability was dete rmined for disease resistance in three snap bean genotypes (Alessa, Hab 52 and Hab 198) and two dry bean genotypes (Bac-6 and A-794). Plants were inoc ulated with highly pathogenic isolate CNF 15, using a razor blade procedure in leaves and needle punctures in pods. They were evaluated 7 days after i noculation. Leaves were evaluated on a 1 to 5 scale and pods by lesion diam eter. Diallel analysis was conducted using Griffing's model. General combin ing ability (GCA) was significant for both leaf and pod infection, whereas specific combining ability (SCA) was significant for disease reaction in po ds. Bac-6 and A-794 were considered superior genotypes for leaf resistance. Nonadditive effects were predominant in pod reactions. and Alessa x Bac-6, Alessa x A-794 and Hab 52 x Bac-6 were the best combinations.