Molecular mapping and intra-cluster recombination between anthracnose race-specific resistance genes in the common bean differential cultivars Mexico 222 and Widusa

Resistance to races 19, 31, 38, 65, 73, 102, and 449, of the pathogenic fungus Colletotrichum lindemuthianum (anthracnose) was evaluated in F3 families derived from the cross between the anthracnose diVerential bean cultivars Mexico 222 (resistant to races 19, 31, and 38) and Widusa (resistant to races 38, 65, 73, 102, and 449). Molecular marker analyses were carried out in the corresponding F2 individuals in order to identify the genes for anthracnose resistance present in these two diVerential cultivars. The results of the combined segregation indicate that the resistance to anthracnose races 19, 31, and 38, present in Mexico 222, is conferred by single dominant race-speciWc genes organized in a cluster located in B4 linkage group, corresponding to the previously described Co-3/Co-9 locus. The resistance to anthracnose races 65, 73, 102, and 449, present in Widusa, is conferred by a dominant gene (or genes) representing a diVerent haplotype of the same Co-3/Co-9 cluster. A single dominant gene located in a position independent from cluster Co-3/Co-9 (probably at the Co-1 locus) confers speciWc resistance to race 38 in Widusa. Recombinants for closely linked resistance speciWcities belonging to the Co-3/Co-9 cluster have been detected. The possibility of pyramiding race-speciWc resistance genes bymeans of intra-cluster recombination, and its potential use in plant breeding, is indicated