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Reaction of Maize Cultivars from Uganda to Exserohilum turcicum. E. Adipala,Former graduate student, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, 44691, Current address: Department of Crop Science, Makerere University, P.O. Box 7062, Kampala, Uganda; P. E. Lipps, and L. V. Madden. professors, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, 44691. Phytopathology 83:217-223. Accepted for publication 19 November 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-217.

Several disease variables were used to characterize the type and level of disease reactions of Ugandan maize cultivars to northern leaf blight, caused by Exserohilum turcicum, in 1989 seedling studies and in 1990 and 1991 field trials. Maize cultivars differed significantly (P ≤ 0.001) in susceptibility as determined by the rate of disease increase (r) for the logistic model, area under disease progress curves, final lesion numbers, and severity ratings. Estimates of r were similar in moderately resistant and susceptible inbreds, Mo17, B73Ht1, and B73 but were significantly (P ≤ 0.001) lower in the Ugandan cultivars Babungo 3, Kawanda composite A (KWCA), and Population 42, indicating that rate-reducing resistance characterized resistance. Similarly, epidemic onset (y*o), indicated by the intercept of the regression equation for logit in relation to time, differed among cultivars, but unlike r, differences were not always significant among susceptible and resistant cultivars. The high level of rate-reducing resistance in Babungo 3, Population 42, and KWCA was effective against both races 0 and 1, and was more effective than the Ht1 gene against race 0. In seedling studies, Babungo 3 delayed formation of necrotic lesions, had fewer and smaller lesions, supported low sporulation, and delayed sporulation by at least 3 days compared with susceptible cultivars. For most genotypes, results for seedling and adult plants were positively correlated. Regardless of assessment method, Babungo 3, Population 42, and KWCA were significantly (P ≤ 0.001) more resistant to E. turcicum than the susceptible check B73, resistant polygenic check Mo17, or monogenic resistant check B73Ht1.