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Effects of Temperature and Light on Virulence of Exserohilum turcicum on Corn. R. P. Thakur, Plant pathologist, Cereals Program, International Crops Research Institute for the Semi-Arid Tropics, Patancheru P.O., Andhra Pradesh 502324, India; K. J. Leonard(2), and S. Leath(3). Research plant pathologists, Department of Plant Pathology, Agricultural Research Service, U.S. Department of Agriculture, Box 7616, North Carolina State University, Raleigh 27695-7616, (2)Present address: Cereal Rust Laboratory, University of Minnesota, St. Paul 55108. Phytopathology 79:631-635. Accepted for publication 16 December 1988. 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, 1989. DOI: 10.1094/Phyto-79-631.

Isolates of races 1, 2, and 4 of Exserohilum turcicum were tested for virulence at day/night temperatures of 22/18 or 26/22 C on seedlings of corn inbreds H4460 and B37 and their backcross lines with the Ht1 gene for resistance. Race 2 was virulent on B37Ht1 at both 22/18 and 26/22 C but avirulent on H4460Ht1 at 26/22 C. Race 2 induced normal susceptible-type lesions on inbreds B37 and H4460 at both 22/18 and 26/22 C, and the number of lesions per plant was greater at reduced light intensities. Seedlings of H4460Ht1 grown at 22/18 C before inoculation became resistant to race 2 if they were transferred to 26/22 C within the first 3 days after inoculation. Conversely, if they were grown at 26/22 C and transferred to 22/18 C within 3 days after inoculation with race 2, they developed normal susceptible-type lesions; if they were transferred later, they developed intermediate- and susceptible-type lesions. If H4460 seedlings were grown at 22/18 C before inoculation, the lengths of lesions induced by races 2 and 4 were significantly correlated with the number of days they remained at 22/18 C before transfer to 26/22 C, but if they were grown at 26/22 C and transferred to 22/18 C, the lesion lengths were not significantly affected by the number of days at 26/22 C after inoculation.

Additional keywords: northern corn leaf blight, Setosphaeria turcica, Zea mays.