RAPD MARKERS LINKED TO 3 MAJOR ANTHRACNOSE RESISTANCE GENES IN COMMONBEAN

Durability of the resistance to anthracnose, caused by Colletotrichum lindemuthianum (Sacc. & Magnus) Lambs.-Scrib., could be increased if m ore than one resistance gene were incorporated into current bean (Phas eolus vulgaris L.) cultivars. The objective of this study was to ident ify random amplified polymorphic DNA (RAPD) markers linked to three in dependent resistance loci to facilitate gene pyramiding in common bean . Markers were identified by means of bulked segregant analysis and he terogeneous 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 faci litate introgression of the Co-1 gene across the Andean and Middle Ame rican Phaseolus gene pools. RAPD marker OAB3(450) was linked in coupli ng-phase (5.9 +/- 1.7 cM) to the Co-5 (Mexique 3) allele. A coupling-p hase (OAH1(780)) and a repulsion-phase (OAK20(890)) RAPD marker were l inked to the Co-6 locus. These markers flanked the Co-6 locus and mapp ed 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 r epulsion-phase (92%) RAPD phenotype. Durability of resistance to anthr acnose could be improved if (i) two major resistance genes were pyrami ded by marker assisted selection, (ii) different genes were deployed i n different regions, and (iii) resistance genes from different gene po ols were combined.