The role of RAPD markers in breeding for disease resistance in common bean

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Diseases are regarded as the leading constraint to increased common bean (Phaseolus vulgaris L.) production worldwide. The range in variability and complexity among bean pathogens can be controlled with different single gene and quantitative resistance sources. Combining these resistance sources into commercial cultivars is a major challenge for bean breeders. To assist breeders, a major effort to identify RAPD markers tightly linked to different genes was undertaken. To date, 23 RAPD and five SCAR markers linked to 15 different resistance genes have been identified, in addition to QTL conditioning resistance to seven major 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 genes to improve their longevity and retain valuable hypostatic genes is discussed. The role of markers linked to the QTL controlling complex resistance and the potential to combine resistance sources using marker based selection is reviewed. Improving levels of selection efficiency using flanking markers, repulsion-phase linkages, co-dominant marker pairs, recombination-facilitated MAS and SCAR markers is demonstrated. Marker-assisted selection for disease resistance in common bean provides opportunities to breeders that were not feasible with traditional breeding methods.