Molecular marker-assisted selection of two bean rust resistance genes with phenotypic masking effects
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abstract
Resistance to rust, caused by Uromyces appendiculatus in dry beans has been shown to originate in germplasm from both Andean (A) and Middle American (MA) regions of Phaseolus vulgaris subdomestication. Two genes, Ur-6 (A) and Ur-7 (MA), cannot be discriminated in MA bean germplasm having the Ur-6 gene. Ur-6 is resistant to more U. appendiculatus races than Ur-7, and thus, the MA gene is masked in the presence of the A gene in MA cultivars and breeding lines with both genes. We previously reported coupling-phase RAPD OBC06.300 and SCAR SOBC06.308 markers tightly linked to Ur-6 present in Olathe, and coupling-phase RAPD OAD12.550 and SCAR SOAD12.537 markers linked (no recombination) to Ur-7 present in Great Northern (GN) 1140. These linked markers to the two genes were used to identify bean lines with both genes. In 90 bean genotypes, linked RAPD and SCAR markers identified MA pinto beans Olathe, Bill Z, Apache, BelDak-RR-1 and 2, and CO 12783 that have Ur-6 and also have Ur-7 due to presence of the two couplingphase markers OAD12.550 and SOAD12.537 for Ur-7. Other pinto lines with Ur-6 such as Burke, Kodiak, Topaz, Golden Gate Wax, BelDakMi lines, and other Colorado breeding lines lack Ur-7 because of absence of the RAPD and SCAR markers for the MA gene. GN1140 as well as pintos US-5 and US-14 are three MA beans that have Ur-7 but not Ur-6 due to absence of the two coupling-phase markers OBC06.300 and SOBC06.308 for Ur-6.
