Genetics of leaf rust resistance in the soft red winter wheat cultivars Coker 9663 and Pioneer 26R61

Leaf rust, caused by the fungus Puccinia triticina, is an important disease of soft red winter wheat cultivars that are grown in the southern and eastern United States. The objectives of this study were to identify the leaf rust resistance genes in two soft red winter wheat cultivars, Coker 9663 and Pioneer 26R61, that have been widely grown and were initially highly resistant to leaf rust. Both cultivars were crossed with the leaf-rust-susceptible spring wheat cv. Thatcher and the F1 plants were crossed to Thatcher to obtain backcross (BC₁) F₂ families. In seedlings, the Thatcher/Coker 9663 BC₁F₂ families segregated for three independent seedling resistance genes when tested with different leaf rust isolates. The leaf rust infection types of selected BC₁F₃ lines, when tested with different leaf rust isolates, indicated that seedling resistance genes Lr9, Lr10, and Lr14a were present. In field plot tests, BC₁F₄ lines that were seedling susceptible had some adult plant resistance to leaf rust. Seedlings of the Thatcher/Pioneer 26R61 BC₁F₂ families segregated for two independent resistance genes. Infection types of selected BC₁F₃ lines indicated the presence of Lr14b and Lr26. The adult plant gene Lr13 was determined to be present in selected BC ₁F₄ lines that were tested with different leaf rust isolates in greenhouse tests.