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Genetic Analysis of Exserohilum turcicum Lesion Expansion on Corn. Kristen M. Sigulas, Graduate student, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; R. R. Hill, Jr., and J. E. Ayers. Research agronomist, Regional Pasture Research Laboratory, USDA, ARS, and Professor, Department of Plant Pathology, respectively, The Pennsylvania State University, University Park 16802. Phytopathology 78:149-153. Accepted for publication 23 July 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-149.

All possible crosses between four corn inbred lines known to differ in reaction to Exserohilum turcicum were made in order to study the genetics of polygenic resistance to the fungus. Inbreds and single crosses were inoculated in the field, at two locations, with a conidial suspension of the pathogen. Lesion measurement commenced 3 wk after inoculation and continued every other day for a total of five measurements. Polynomial curve fitting of the lesion expansion data was used to estimate genetic effects. Lesion area, lesion expansion rate, and the shape of the lesion area expansion curve appeared to be under host genotype control. By means of regression techniques, the data were fitted to four genetic models. All the models had significant deviations from regression; the mean squares for deviations were smallest for the model that assumed additive and unequal genetic effects. Diallel analysis showed that general combining ability effects were much larger than specific combining ability effects. The results indicate that genetic analyses of lesion expansion curves would provide more information than analyses at a given time.

Additional keywords: Helminthosporium turcicum, horizontal resistance, maize, northern leaf blight, quantitative inheritance, Zea mays.