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A Comparison of Monogenic and Polygenic Resistance to Helminthosporium turcicum in Corn. A. J. Ullstrup, Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907. Phytopathology 60:1597-1599. Accepted for publication 2 June 1970. DOI: 10.1094/Phyto-60-1597.

Both monogenic and polygenic resistance to infection by Helminthosporium turcicum are present in corn germplasm. Monogenic resistance is characterized by small necrotic lesions surrounded by distinct and extensive chlorotic halos. Little, if any, sporulation occurs in the necrotic lesions. Polygenic resistance is expressed as a reduction in numbers of lesions without marked diminution in size over those developed on susceptible genotypes. In comparative yield trials conducted for 3 years, single crosses possessing polygenic resistance averaged, respectively, 57.1, 27.3, and 58.0 bushels/acre more than the average yields of fully susceptible single crosses in the presence of epiphytotics of northern corn leaf blight. The corresponding average yield increases of single crosses bearing monogenic resistance, over the average yield of the susceptibles, were 38.0, 20.9, and 37.6 bushels/acre. The extensive chlorosis accompanying infection of genotypes carrying monogenic resistance may have a debilitating effect which is reflected in lower grain yield. Severity of leaf blight was positively associated with yield reduction.

Additional keywords: northern corn leaf blight, disease resistance.