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Identification and Application of a Random Amplified Polymorphic DNA Marker for the I Gene (Potyvirus Resistance) in Common Bean. Scott D. Haley, Department of Crop and Soil Sciences, Michigan State University, East Lansing 48824, Permanent address: Plant Science Department, South Dakota State University, Brookings 57007; Lucia Afanador, and James D. Kelly. Department of Crop and Soil Sciences, Michigan State University, East Lansing 48824. Phytopathology 84:157-160. Accepted for publication 2 November 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-157.

The dominant inhibitor I gene has recently become a liability for common bean (Phaseolus vulgaris) cultivars infected with temperature-insensitive, necrosis-inducing strains of bean common mosaic virus (BCMV). Although cultivars with the I gene can be protected from hypersensitive lethality by recessive resistance genes, the most broadly effective resistance gene combination (I and bc-3 genes) is difficult to identify due to epistasis (dominance with epistasis of bc-3/bc-3 over I/; hypostasis). Our objectives were to identify a molecular marker linked to the I gene and to evaluate indirect selection with the marker to facilitate pyramiding of the I and bc-3 resistance genes. Pairs of near-isogenic lines with and without the I gene were screened with random decamer primers in the polymerase chain reaction to identify linked random amplified polymorphic DNA (RAPD) markers. A single RAPD marker was identified (OW13690, generated by a 5-CACAGCGACA-3 decamer) and found to be tightly linked in coupling with the I gene in five segregating populations (recombination from 1.3 0.8 to 5.0 2.2 centimorgans). Selections from complex backcross populations, made for the presence of bc-3/bc-3 genotypes, were also assayed for OW13690 to identify selections carrying the hypostatic I gene. Our results demonstrate the utility of RAPD markers when used as indirect selection criteria for pyramiding epistatic BCMV resistance genes.