Postulation of leaf rust resistance genes in selected soft red winter wheats

Leaf rust, caused by the fungus Puccinia triticina Eriks., is a major disease nearly wherever wheat (Triticum spp.) is grown in the USA. Soft red winter wheat (T. aestivum L.) cultivars with varying degrees of leaf rust resistance are grown in the southern USA. The objective of this study was to characterize the seedling leaf rust resistance present in a group of 35 soft red winter wheat cultivars and 17 breeding lines. Leaf rust infection types (ITs) produced on the cultivars and lines by 16 P. triticina isolates were compared with the ITs produced on a standard set of 'Thatcher' near-isogenic lines that differed for single leaf rust resistance genes. Seedling resistance genes Lr1, Lr2a, Lr9, Lr10, Lr11, Lr18, and Lr26 were postulated to be present in the soft red winter wheat cultivars and lines. Adult plant leaf rust resistance for the cultivars and lines was assessed in field plots at two locations in North Carolina in 2000. Wheat cultivars postulated or genetically determined to have the adult plant resistance genes Lr12 and Lr34 had effective leaf rust resistance in the field plots. The soft red winter wheat cultivars and lines that had seedling resistance genes Lr2a, Lr9, and Lr26 combined with adult plant resistance were highly resistant to leaf rust. Cultivars and breeding lines that had seedling resistance genes Lr1, Lr10, Lr11, and Lr18 combined with adult plant resistance had moderate to low levels of leaf rust resistance.