RAPD markers linked to three major anthracnose resistance genes in common bean

Durability of the resistance to anthracnose, caused by Colletotrichum lindemuthianum (Sacc. & Magnus) Lambs.-Scrib., could be increased if more than one resistance gene were incorporated into current bean (Phaseolus vulgaris L.) cultivars. The objective of this study was to identify random amplified polymorphic DNA (RAPD) markers linked to three independent resistance loci to facilitate gene pyramiding in common bean. Markers were identified by means of bulked segregant analysis and heterogeneous inbred populations. RAPD marker OF10(530) cosegregated in repulsion-phase (1.9 +/- 1.4 cM) with the Co-1 (A) allele. A survey of diverse bean genotypes showed that the OF10(530) RAPD band could facilitate introgression of the Co-1 gene across the Andean and Middle American Phaseolus gene pools. RAPD marker OAB3(450) was linked in coupling-phase (5.9 +/- 1.7 cM) to the Co-5 (Mexique 3) allele. A coupling-phase (OAH1(780)) and a repulsion-phase (OAK20(890)) RAPD marker were linked to the Co-6 locus. These markers flanked the Co-6 locus and mapped at 12.3 +/- 1.9 from the Co-6 allele and at 7.3 +/- 1.5 cM from the co-6 allele, respectively. Coupling and repulsion-phase RAPD markers used as a codominant pair showed a higher selection efficiency (95%), for the identification of homozygous (Co-6 Co-6) F-2 individuals, than individual selection either for a coupling-phase (33%) or against a repulsion-phase (92%) RAPD phenotype. Durability of resistance to anthracnose could be improved if (i) two major resistance genes were pyramided by marker assisted selection, (ii) different genes were deployed in different regions, and (iii) resistance genes from different gene pools were combined.