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Ecology and Epidemiology

Development of an Infection Model for Cercospora carotae on Carrot Based on Temperature and Leaf Wetness Duration. O. Carisse, Graduate student, Department of Plant Science, Macdonald College of McGill University, 21111 Lakeshore Road Ste-Anne-de-Bellevue, Quebec, Canada, H9X 1C0; A. C. Kushalappa, associate professor, Department of Plant Science, Macdonald College of McGill University, 21111 Lakeshore Road Ste-Anne-de-Bellevue, Quebec, Canada, H9X 1C0. Phytopathology 80:1233-1238. Accepted for publication 25 June 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1233.

Leaves of carrot (Daucus carota L. var. Sativa DC.), cv. Dagger, were inoculated with a conidial suspension (10⁴ conidia/ml) of Cercospora carotae and incubated at various combinations of temperatures (16?32 C) and leaf wetness durations (12?96 hr). Infection was quantified by counting the number of lesions per inoculated leaf. In general, the lesion number increased with an increase in temperature and wetness duration, except at 32 C, where the lesion number decreased with an increase in wetness duration. Plants incubated at 16 and 32 C developed only 8% of the total number of lesions (all temperatures and wetness durations). A polynomial model (using arcsin ?Y transformation) and the Richards function were evaluated for reliability in describing infection as a function of temperature and leaf wetness duration. The Richards model fit the data better and was more relevant biologically.