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Effects of Temperature, Dew Period, and Light on the Growth and Development of Alternaria helianthi. S. J. Allen, Junior research fellow, Department of Botany, University of New England, Armidale, N.S.W. 2351, Australia; J. F. Brown(2), and J. K. Kochman(3). (2)Associate professor, Department of Botany, University of New England, Armidale, N.S.W. 2351, Australia; (3)Senior plant pathologist, Queensland Department of Primary Industries, Toowoomba, Queensland, 4350, Australia. Phytopathology 73:893-896. Accepted for publication 29 November 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-893.

Alternaria blight is a serious disease of sunflower (Helianthus annuus) in northeastern Australia, particularly during summer. The germination of conidia of Alternaria helianthi was favored by temperatures between 25 and 28 C and by the presence of free water on the leaf surface. Colony growth of A. helianthi on PDA was greatest at 25 C. A 12-hr period of leaf wetness was required to give the maximum infection (lesions per square centimeter) at 25 and 28 C. Repeated periods of dew and high relative humidity promoted the expansion of lesions. The generation time for A. helianthi on sunflower leaf disks was less than 2 days at 22 and 25 C. Artificial light had no significant effect on percent germination of conidia, but increased the number of germ tubes produced by each conidium and the growth of mycelium on PDA. The environmental conditions that favor A. helianthi occur in northeastern Australia during the summer, when mean daily temperatures are 25- 30 C and extended periods of wet weather associated with rainbearing cyclonic depressions are common. A method of reducing losses caused by A. helianthi, based on time of sowing, is suggested.