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Inheritance of Anthracnose Resistance in Common Bean Differential Cultivar AB 136

Inheritance of anthracnose resistance of the common bean (Phaseolus vulgaris L.) differential cultivar AB 136 to races 89, 64, and 73 (binary system designation) was studied in crosses with the susceptible differential cultivars Michelite (race 89), Mexico 222 (race 64), and Cornell 49-242 (race 73). In each cross two progenitors, the F₁, F₂, and backcross-derived plants were inoculated with the respective race under environmentally controlled greenhouse conditions. The results indicate that single dominant gene(s) control resistance to races 89 and 64, giving a segregation ratio of 3:1 in the F₂, 1:0 in the backcrosses to AB 136, and 1:1 in the backcross to Michelite (race 89), and to Mexico 222 (race 64). For race 73, the following segregation ratios between resistant and susceptible plants were observed: 13:3 in the F₂, 1:0 in the backcross to AB 136, and 1:1 in the backcross to Cornell 49-242. Such results suggest that two independent genes may determine resistance of AB 136 to race 73, one dominant (Co-6) and one recessive that is proposed to be assigned co-8. Genotypes Co-6_ or co-8 co-8 would condition resistance, whereas susceptibility would be present in genotypes co-6 co-6 Co-8_. Given the dominant nature of anthracnose resistance genes present in line AB 136 and its resistance to 25 races of Colletotrichum lindemuthianum identified in Brazil by other researchers, we included this cultivar as one of the donor parents in our molecular marker-assisted backcross breeding program, to develop common bean cultivars resistant to anthracnose and adapted to Central Brazil.