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Biotic and Environmental Factors Affecting Infection of Sweet Corn with Exserohilum turcicum. Yehouda Levy, Lecturer, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 100, Israel; Yigal Cohen, professor, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 100, Israel. Phytopathology 73:722-725. Accepted for publication 20 December 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-722.

Optimal temperatures for conidial germination and appressorial formation of Exserohilum turcicum on leaves of the susceptible corn cultivar Jubilee were 25 and 15 C, respectively, whereas that for infection peg formation on corn leaf impressions was 20 C. The minimal dew period required for these processes at the corresponding optimal temperatures was 1, 3, and 4 hr, respectively. Conidial germination and infection peg formation were not affected by leaf and plant age, but under laboratory conditions, appressorial formation was favored in younger plants that were also more susceptible to the blight incited by the fungus. Infection occurred at 15- 30 C with an optimum at 20 C. A 5-hr dew period at 20 C was required for lesion formation. The number of lesions increased with lengthening dew period and increasing inoculum concentration, but under all combinations of dew period and inoculum concentration, the number of lesions was largest at 20 C. Our results indicate that environmental conditions in Israel during the growing season (May- October) are favorable for infection. Epidemic outbreaks of the blight do not occur until late August when dew periods are long enough for fungal sporulation.

Additional keywords: epidemiology, northern corn leaf blight.