Inheritance of resistance to the widely distributed race 6 of Pseudomonas syringae pv. phaseolicola in common bean pinto US14HBR6

Halo blight disease of common bean (Phaseolus vulgaris L.) is caused by Pseudomonas syringae pv. phaseolicola (Psp) and is found worldwide in bean growing regions with temperate climates, such as the Midwestern United States. In situations where high levels of primary inoculum are present (e.g., in seed) and the climate is favorable, yield losses as high as 45% have been reported for susceptible cultivars. Disease resistance is the most desirable management strategy, and resistant cultivars and germplasm to some Psp races are available. However, high levels of resistance to Psp race 6, one of the most prevalent and economically important races, are not present in available cultivars. Here, we report the inheritance of a newly described source of resistance to Psp race 6 in the recently registered common bean pinto US14HBR6. The inheritance of resistance in US14HBR6 was investigated by making crosses between resistant (R) US14HBR6 and the susceptible (S) breeding line 92BG-7 and inoculating the parents, F-1, F-2, F-3, and the respective backcrosses to either parent with Psp race 6. All 159 F-1 plants were susceptible, the F-2 segregated into 237S:16R and the F-3 segregated into 309S:26R. The US14HBR6*2 x 92BG-7 F-1 segregated into 83S:41R, and the US14HBR6 x 92BG-7*2 F-1 segregated into 116S:0R. Together, these results suggest that the resistance to Psp race 6 in US14HBR6 is controlled by two independently inherited recessive genes. Evidence is also presented that dominant alleles of these resistance genes, at one or both loci, contribute to dosage-dependent susceptibility to halo blight. These halo blight resistance genes can be used in the development of common bean germplasm and cultivars with high levels of resistance to Psp race 6. In combination with other race-specific and non-race specific resistance genes from diverse Phaseolus germplasm, these genes could also be used to generate germplasm lines and cultivars with resistance to all known races of Psp.