Molecular markers and allelic relationships of anthracnose resistance gene cluster B4 in common bean

Allelism tests and molecular marker analyses were combined to characterize the genes that, proceeding from the germplasm lines ‘A493’ and ‘A321’, confer resistance to bean anthracnose in the new breeding lines ‘A1220’ and ‘A1231’, respectively, developed through backcross breeding, using the dry bean landrace ‘Andecha’ as the recurrent parent. Allelism tests indicate that resistance to race 38 of anthracnose in genotypes ‘A1220’, ‘A1231’, and ‘BAT 93’ and in the differential cultivars ‘PI 207262’ and ‘Mexico 222’ is determined by different dominant alleles at the same locus. Therefore, the results obtained suggest that the so far considered as different genes Co-3 (described as present in ‘Mexico 222’) and Co-9 (described as present in ‘BAT 93’) are alleles of the same gene. RAPD markers OB12350, OAH181100, and OY171100 and SCAR markers SI19 and SW12 were found to be linked to the resistance gene. Data indicate that the resistance genes to race 38 present in these materials are alleles of the same R gene cluster located in linkage group B4, because markers OY171100, SI19 and SW12 were previously linked to this cluster. The SCAR markers SB12 and SAH18 were developed from RAPDs OB12350 and OAH181100, respectively, and a genetic map including the resistance gene and markers SB12, OY171100, SAH18, SW12 and SI19 was made using a F2 segregating population of 72 individuals derived from the cross ‘Andecha’ × ‘A493’.