Recombination-facilitated RAPD marker-assisted selection for disease resistance in common bean

The use of RAPDs (random amplified polymorphic DNA) for indirect selection of disease resistance in common bean (Phaseolus vulgaris L.) is often limited by the amplification in susceptible germplasm of Dlr;A fragments equal in size to the resistance-linked markers. We investigated whether a recombinant individual, with recessive resistance (bc-3bc-3) to bean common mosaic virus, but lacking the RAPD OAD19(690) originally linked in repulsion, would enable indirect selection when crossed to a susceptible cv. C-20 with an amplified fragment equal in size to OAD19(690). Similar use of a recombinant for the marker OS13(660), originally linked in coupling but now in repulsion with bc-3, was investigated. Each marker segregated in reverse orientation with bc-3 in a single population as the resistant parent was recombinant for both RAPDs. In the resulting F-2 population of 81 individuals, OAD19(690), originally in repulsion, now cosegregated in coupling with the bc-3 allele, and could be used to obtain resistant progeny by selecting against it. Conversely, OS13(660), originally in coupling, now cosegregated in repulsion. The strategy of recombination-facilitated marker-assisted selection has the potential to: (i) overcome limited use of dominant RAPD markers by broadening their range of application across all susceptible genotypes, (ii) change linkage orientation of a dominant RAPD marker to that with the greatest selection efficiency for a particular breeding program, and (iii) indicate whether a RAPD marker and same-sized fragment assort independently or are amplified from the same or nearby genomic region.