Markers linked to the bc-3 gene conditioning resistance to bean common mosaic potyviruses in common bean

Necrotic strains of bean common mosaic potyviruses are becoming increasingly problematic in bean growing areas of Africa and Europe. Pyramiding epistatic resistance genes provides the most effective long-term strategy for disease control against all known strains of the virus. Indirect selection using tightly linked markers should facilitate the breeding of desired epistatic resistance gene combinations. In common bean, the most effective strategy for broad spectrum control of the bean common mosaic potyviruses is to combine I and bc-3 genes. We describe the use of near-isogenic lines and segregating populations from different gene pools combined with bulked segregant analysis to identify markers tightly linked with the recessive bc-3 gene that conditions resistance to all strains of bean common mosaic necrosis virus. We identified a RAPD marker, OG6595, linked at 3.7 cM from the bc-3, and the marker was used to confirm the location of bc-3 gene on bean linkage group B6. A codominant AFLP marker, EACAMCGG-169/172was identified and linked at 3.5 cM from the bc-3 and the AFLP and OG6595 markers flanked the bc-3 gene. The AFLP marker was converted to the STS marker SEACAMCGG-134/137 which showed co-segregation with the original AFLP marker. The 134 bp fragment associated with resistance was linked with the bc-3 gene present in a diverse group of bean genotypes except in two kidney bean lines. The OG6595 marker mapped on B6 supported independence of bc-3 from the I gene located on B2, which provides the opportunity to readily combine both genes in a single bean cultivar for broad spectrum resistance to bean common mosaic potyviruses