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Ecology and Epidemiology

Influence of Temperature, Leaf Wetness, and High Relative Humidity Duration on Sporulation of Cercospora carotae on Carrot Leaves. O. Carisse,Research assistant, Department of Plant Science, Macdonald Campus of McGill University, 21 111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, Canada, H9X 1C0, Present address: Research Station, Agriculture Canada, 430 Gouin Boul., St-Jean-sur-Richelieu, Canada, J3B 3E6; A. C. Kushalappa(2), and D. C. Cloutier(3). (2)Associate professor, Department of Plant Science, Macdonald Campus of McGill University, 21 111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, Canada, H9X 1C0; (3)Research scientist, Research Station, Agriculture Canada, C.P.3398, L'Assomption, Canada, J0K 1G0. Phytopathology 83:338-343. Accepted for publication 30 November 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-338.

The influence of temperature (1632 C) and duration of moist period (696 h) on sporulation of Cercospora carotae was quantified on carrot plants under three types of moisture conditions (leaf wetness, 96% relative humidity [RH], and 96% RH with an initial 12 h of leaf wetness). Sporulation was quantified as the number of spores per lesion and then transformed to proportion of maximum number of spores (PMS). The highest PMS (1.78 103 spores/lesion) was obtained at 28 C after 96 h of leaf wetness. The effect of leaf wetness and 96% RH duration on sporulation was similar for most of the temperatures, except that no sporulation was observed at any time at 16 and 32 C for 96% RH. Under each moisture condition, PMS increased with increasing temperature up to the optimum (28 C) and then declined. The presence of an initial 12 h of leaf wetness enhanced sporulation and accelerated the beginning of sporulation as compared to continuous 96% RH. The PMS was modeled as a nonlinear logistic function of time for the leaf wetness (R2 = 0.98) and 96% RH moisture conditions (R2 = 0.97). A polynomial model was used to describe sporulation as a function of temperature and duration of 96% RH with initial 12 h of leaf wetness (R2 = 0.95).

Additional keywords: quantitative epidemiology.