The objective of this study is to develop a molecular marker linked to the Co-1² gene, from the Andean anthracnose differential cultivar Kaboon and to characterize the anthracnose resistance in the Andean cultivar JaloEEP558. Amplified Fragment Length Polymorphism (AFLP), Simple Sequence Repeat (SSR) and Random Amplification of Polymorphic DNA (RAPD) markers were employed to find a marker linked to the Co-1² locus. The AFLP marker, E_ACTM_CCA-108/107, linked at 9.9 cm from the Co-1² gene was identified. To expedite the process of mapping, the Sequence Tagged Site (STS) marker, SE_ACTM_CCA, was derived from E_ACTM_CCA-108/107. The STS marker is not allele specific and both markers appear to be gene pool specific. We speculate that the low level of polymorphism observed near the Co-1 locus is due to its proximity to a block of highly conserved domestication genes. The anthracnose resistance in the Andean cultivar JaloEEP558 was characterized using a combination of traditional and molecular techniques. Inoculation with various races of Colletotrichum lindemuthianum revealed that JaloEEP558 carried an allele of the Co-1 locus, most likely the same allele as that carried by Michigan Dark Red Kidney (MDRK carries Co-1). Inoculation of the F₂ population derived from EEP558/ Perry Marrow (Co-1³ ), with race 357, revealed that resistance to race 357 in JaloEEP558 is conditioned either by a single dominant gene or two epistatic genes, one dominant and one recessive. Lack of segregation for resistance in the allelism tests conducted in the JaloEEP558/MDRK F₂ population inoculated with race 73 suggests that resistance is conditioned by an allele of the Co-1 locus.

Anthracnose, caused by the hemibiotrophic fungus Colletotrichum lindemuthianum, is considered the most economically important disease of common bean worldwide. This is due, in part, to the seed-borne nature and pathogenic variability of C. lindemuthianum. Genetic resistance is the best form of control, especially in areas of subsistence farming where commercial seed production and the certified seed industry are absent. Pyramiding of anthracnose resistance genes of Andean and middle American origin has been proposed as a strategy for broad-based durable resistance breeding (Young and Kelly, 1996a and1996b). Many middle American anthracnose resistance genes have been characterized, Co-2 through Co-11, (Kelly and Vallejo, 2004; and Gonçalves-Vidigal et al., 2007). However, very few Andean anthracnose resistance genes have been identified. New sources of resistance, therefore, are always being sought (Pathania et al., 2006) to provide the bean breeders with novel genetic resources for anthracnose resistance breeding.

The Co-1 locus is complex with five characterized alleles (Kelly and Vallejo, 2004; Gonçalves-Vidigal and Kelly, 2006), each conferring resistance to a different range of C. lindemuthianum races. Among the Andean cultivars, Kaboon was shown to be highly resistant to anthracnose, defeated by only two of the 40 races tested (Balardin et al., 1997). The major dominant gene conditioning resistance in Kaboon is reported to be Co-12, an allele of the Co-1 gene (Melotto and Kelly, 2000). The Andean bean cultivar, JaloEEP558, used as a parent in the mapping population of the bean integrated map also displays resistance to anthracnose (Freyre et al., 1998) and may provide a new source of resistance in the Andean gene pool. To facilitate genetic mapping and resistance breeding, markers tightly linked to the major resistance genes such as, Co-1 are needed.

Molecular markers linked to the Co-1 locus have been previously identified (Random Amplification of Polymorphic DNA(RAPD): Young and Kelly, 1997; and AFLP: Mendoza et al., 2001). Yet, these markers are linked in the repulsion phase and lack reproducibility between laboratories. Mendez de Vigo (2001) used the same repulsion marker F10530 to map the Co-1 locus to bean linkage group B1. Recently, Geffroy et al. (2008) mapped the Co-x gene from JaloEEP558 to the distal end of B1, using the PROE8b marker linked at 12.4 cm. Since different strains of anthracnose and markers were used to map the Co-x, and Co-1 genes to B1 we cannot assume that the genes are the same or are allelic. We can only concur with the author that the genes are tightly linked. The availability of other more reproducible markers linked in the coupling phase would greatly facilitate mapping and the introgression of the Co-1 gene into gene pyramids for anthracnose resistance using the Marker-Assisted Selection (MAS).

Molecular Tagging, Anthracnose Resistance Locus, Hemibiotrophic fungus, Colletotrichum lindemuthianum, Amplified Fragment Length Polymorphism, AFLP, Random Amplification of Polymorphic DNA, RAPD, Phaseolus vulgaris, Marker-assisted selection, MAS, Michigan Dark Red Kidney, MDRK, Potato Dextrose Agar, PDA, DNA polymerase, QTL Analysis .