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Resistance

Differences in Resistance Between Maize Hybrids With or Without the Ht₁ Gene When Infected With Exserohilum turcicum Race 2. S. Leath, Department of Plant Pathology, University of Illinois, Urbana 61801; W. L. Pedersen, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 76:257-260. Accepted for publication 28 August 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-257.

There are three known races of Exserohilum turcicum, causal organism of northern leaf blight of maize (NLB); races 1 and 3 are avirulent and race 2 is virulent on maize with the Ht₁ gene. Field studies were conducted in 1982 and 1983 to determine the effectiveness of the Ht₁ gene in conditioning resistance to races 1 and 2 of E. turcicum. Lesion expansion rates were significantly smaller for hybrids with the Ht₁ gene than for hybrids made from their recurrent parents without the Ht₁ gene when inoculated with race 1. With E. turcicum race 2, lesion length, area, and expansion rate and area under the disease progress curve were significantly lower for the hybrid A632Ht₁ x A619Ht₁ than for its near-isogenic counterpart A632 x A619, which is susceptible to E. turcicum. Significant differences in quantitative resistance between hybrid sets also were detected. In greenhouse studies, similar results were obtained for lesion length and disease efficiency. Significant yield differences were detected between A632Ht₁ x A619 and A632 x A619 when inoculated with E. turcicum race 2.