DETECTION OF GENES FOR RESISTANCE TO COMMON BACTERIAL-BLIGHT OF BEANS

One of the most important diseases of common bean (Phaseolus vulgaris L,) in tropical and sub-tropical regions is common bacterial blight (C BB), which is caused by Xanthomonas axonopodis pv, phaseoli (= X. camp estris pv, phaseoli). Useful sources of resistance to CBB have been fo und in the related species P. coccineus Lam, and P, acutifolius A. Gra y. Despite the complexity of their inheritance, these resistances have been introgressed into bean breeding lines, 'XR-235-1-1' is a Mesoame rican bean breeding line that carries P. coccineus-derived oligogenic resistance to CBB, We have analyzed the linkage relationships between 117 DNA marker loci and CBB resistance genes in a recombinant inbred f amily obtained between XR-235-1-1 and 'Calima', a susceptible Andean g enotype, Two genes for resistance to CBB from XR-235-1-1 were detected , one linked to Bng40 in Group A, and the other to Bng139 in Group F,S urprisingly, the effect of two Calima-derived resistance genes, linked to Bng25a and Bng154 in Group J, was also detected. Analysis of sever al models with these resistances pointed to the most efficient model t hat explained at least 40% of the variation for resistance to CBE and included the two XR-derived resistances and the Bng154-linked Calima-d erived resistance. Marker assisted selection is proposed for introgres sion of resistance genes into susceptible backgrounds.