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Disease Development and Yield Losses Associated with Northern Leaf Blight on Corn. J. M. Perkins, Assistant Plant Pathologist, Department of Plant Pathology, University of Illinois, Urbana 61801. W. L. Pedersen, Assistant Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Plant Dis. 71:940-943. Accepted for publication 4 June 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0940.

Three single-cross corn (Zea mays) hybrids, with and without the Ht resistance gene, were inoculated with conidial suspensions of Exserohilum turcicum race 1 at one of five growth stages in 19791982. Greater initial lesion numbers were observed on the Ht versions of the three hybrids than on the ht versions. Area under the disease progress curve (AUDPC) was greater for the ht versions of the hybrids than for the Ht versions. A619 A632 had the highest AUDPC values, a result of low polygenic resistance. Significant reductions in grain yields and 500-kernel weights were observed only for A619 A632, and yield reductions ranged from 0 to 18%. Critical-point (CP) and AUDPC models were evaluated using untransformed and transformed data. The best model was obtained using AUDPC (Y = 92.97 0.12 (AUDPC), r2 = 0.68). CP models using percent leaf area infected at 3, 5, and 6 wk after midsilk also gave relatively good fit (r2 = 0.66).