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Characterization of the Genetic Resistance to Colletotrichum lindemuthianum in Common Bean Differential Cultivars. Roberto A. Young, Research Associate, Department of Horticulture, Michigan State University, East Lansing 48824. James D. Kelly, Professor, Department of Crop and Soil Sciences, Michigan State University, East Lansing 48824. Plant Dis. 80:650. Accepted for publication 13 March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0650.

The inheritance of genetic resistance to bean anthracnose in genotypes Catrachila and SEL 1360 derived from two anthracnose differential cultivars, AB 136 and G 2333, respectively, is described. Segregation data from three different F2 populations and their respective F2:3 families indicated that a single dominant gene is responsible for the anthracnose resistance in Catrachita. In the lest for allelism, chi-square lest confirmed that the single dominant resistance gene in Catrachita was situated at a different locus from previously characterized resistance genes A, Are, Mexique I, Mexique 2, and Mexique 3. It is proposed that the single dominant resistance gene present in Catrachita be assigned the genetic symbol Co-6, Co for Colletotrichum and 6 because it is the sixth major anthracnose resistance gene characterized and reported in the literature. Segregation in the three F2 populations where SEL 1360 was used as the resistant parent fitted a 3:1 (R-:rr) ratio and a 1:2:1 (RR:Rr:rr) ratio in the F2:3 families. Segregation data suggested that a single dominant gene was conditioning resistance to anthracnose in SEL 1360. The test for allelism involving SEL 1360 indicated that Ihe single dominant gene in SEL 1360 is independent from A (Co-1), Are (Co-2), Mexique I (Co-3), and Mexique 2 (Co-4) genes. However, the dominant gene in SEL 1360 did not segregate independently from the resistance gene Mexique 3 in the differential cultivar TU, demonstrating that both dominant alleles are located at the same locus. Deployment of major genes of Middle American origin, such as Co-6 and Mexique 3 (Co-5), in different combinations with other characterized genes of Andean origin is possible and should contribute to more durable anthracnose resistance in common bean.