Bc-1 and Bc-u—Two Loci Controlling Bean Common Mosaic Virus Resistance in Common Bean are Linked

Abstract

Resistance to bean common mosaic virus (BCMV) strain NY15 (Zaumeyer) and bean common mosaic necrosis virus (BCMNV) strain NL-3 (Drijfhout) was assessed in 98 F 5:6 recombinant inbred lines (RILs) derived from a cross between pinto bean ( Phaseolus vulgaris L.) cultivars `Olathe' and `Sierra'. `Olathe' has bc-u and bc-1 2 whereas `Sierra' has no known resistance genes. The differentiation of resistant and susceptible lines was based on visual symptoms, virus titer, and top dry weight. Forty-seven RILs were moderately resistant to NL-3, while 51 RILs were susceptible. This segregation fits a 1 susceptible: 1 resistant ratio characteristic of a single gene. Sixty-nine RILs were susceptible to NY15, while 29 RILs were resistant, which fits a 3 susceptible: 1 resistant ratio characteristic of a two-gene model. Moderate resistance to NL-3 was conferred by bc-1 2 with or without bc-u present. Bulked segregant and two point linkage analysis identified randomly amplified polymorphic DNA (RAPD) markers linked in coupling to the Bc-1 and Bc-u alleles. The OH14 1100 RAPD marker was 4.5 cM from the Bc-1 locus. The OC16 1000 RAPD marker was linked at a distance of 10.9 cM from the Bc-u locus. Multipoint analysis, using segregation data for bc-1 2 , bc-u , and the two markers, estimated the distance between the Bc-1 and Bc-u loci as 22.8 cM.