THE ROLE OF RAPD MARKERS IN BREEDING FOR DISEASE RESISTANCE IN COMMONBEAN

Diseases are regarded as the leading constraint to increased common be an (Phaseolus vulgaris L.) production worldwide. The range in variabil ity and complexity among bean pathogens can be controlled with differe nt single gene and quantitative resistance sources. Combining these re sistance sources into commercial cultivars is a major challenge for be an breeders. To assist breeders, a major effort to identify RAPD marke rs tightly linked to different genes was undertaken. To date, 23 RAPD and five SCAR markers linked to 15 different resistance genes have bee n identified, in addition to QTL conditioning resistance to seven majo r pathogens of common bean. We review the feasibility of using marker- assisted selection (MAS) to incorporate disease resistance into common bean. Indirect selection of single resistance genes in the absence of the pathogen and the opportunity afforded breeders to pyramid these g enes to improve their longevity and retain valuable hypostatic genes i s discussed. The role of markers linked to the QTL controlling complex resistance and the potential to combine resistance sources using mark er based selection is reviewed. Improving levels of selection efficien cy using flanking markers, repulsion-phase linkages, co-dominant marke r pairs, recombination-facilitated MAS and SCAR markers is demonstrate d. Marker-assisted selection for disease resistance in common bean pro vides opportunities to breeders that were not feasible with traditiona l breeding methods.