RECOMBINATION-FACILITATED RAPD MARKER-ASSISTED SELECTION FOR DISEASE RESISTANCE IN COMMON BEAN

The use of RAPDs (random amplified polymorphic DNA) for indirect selec tion of disease resistance in common bean (Phaseolus vulgaris L.) is o ften limited by the amplification in susceptible germplasm of Dlr;A fr agments equal in size to the resistance-linked markers. We investigate d whether a recombinant individual, with recessive resistance (bc-3bc- 3) to bean common mosaic virus, but lacking the RAPD OAD19(690) origin ally 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), or iginally linked in coupling but now in repulsion with bc-3, was invest igated. Each marker segregated in reverse orientation with bc-3 in a s ingle population as the resistant parent was recombinant for both RAPD s. In the resulting F-2 population of 81 individuals, OAD19(690), orig inally in repulsion, now cosegregated in coupling with the bc-3 allele , and could be used to obtain resistant progeny by selecting against i t. Conversely, OS13(660), originally in coupling, now cosegregated in repulsion. The strategy of recombination-facilitated marker-assisted s election has the potential to: (i) overcome limited use of dominant RA PD markers by broadening their range of application across all suscept ible genotypes, (ii) change linkage orientation of a dominant RAPD mar ker to that with the greatest selection efficiency for a particular br eeding program, and (iii) indicate whether a RAPD marker and same-size d fragment assort independently or are amplified from the same or near by genomic region.