Genetics of leaf rust resistance in spring wheat cultivars alsen and norm

Alsen is a recently released spring wheat cultivar that has been widely grown in the United States because it has resistance to Fusarium head blight and leaf rust caused by Puccinia triticina. Norm is a high yielding wheat cultivar that has been very resistant to leaf rust since it was released. Alsen and Norm were genetically examined to determine the number and identity of the leaf rust resistance genes present in both wheats. The two cultivars were crossed with leaf rust susceptible cv. Thatcher and F₁ plants were backcrossed to Thatcher. Eighty one and seventy three BCF₁ of Thatcher x Alsen and Thatcher x Norm respectively, were selfed to obtain BCF₂ families. The BCF₂ families were tested as seedlings with different isolates of P. triticina that differed for virulence to specific leaf rust resistance genes. The BCF₂ families that lacked seedling resistance were also tested as adult plants in greenhouse tests and in a field rust nursery plot. Segregation of BCF₂ families indicated that Alsen had seedling genes Lr2a, Lr10, and Lr23 and adult plant genes Lr13 and Lr34. Norm was determined to have seedling genes Lr1, Lr10, Lr16, and Lr23 and adult plant genes Lr13 and Lr34. The characterization of Lr23 in the segregating populations was complicated by the presence of a suppressor gene in Thatcher and the high temperature sensitivity of resistance expression for this gene. The effective leaf rust resistance in Alsen is due to the interaction of Lr13 and Lr23, with Lr34; and the effective leaf rust resistance in Norm is due to the interaction of Lr13, Lr16, and Lr23, with Lr34.