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Ecology and Epidemiology

Effects of Temperature and Leaf Wetness Duration on the Infection of Celery by Septoria apiicola. D. Mathieu, Graduate student, Department of Plant Science, Macdonald Campus of McGill University, 21, 111 Lakeshore Road, Ste-Anne-de-Bellevue, Québec, Canada H9X 3V9; A. C. Kushalappa, associate professor, Department of Plant Science, Macdonald Campus of McGill University, 21, 111 Lakeshore Road, Ste-Anne-de-Bellevue, Québec, Canada H9X 3V9. Phytopathology 83:1036-1040. Accepted for publication 24 May 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1036.

The effect of temperature during various leaf wetness periods on the infection of celery (Apium graveolens) by Septoria apiicola was studied by inoculating plants with a suspension of 20,000 conidia per milliliter and incubating at five temperatures (10, 15, 20, 25, and 30 C) and for five wetness periods (12, 24, 48, 72, and 96 h). The number of lesions increased with temperature up to 25 C and then diminished. At each temperature, lesions increased in number with increasing leaf wetness duration, except at 25 and 30 C at which fewer lesions appeared after 72 and 48 h of wetness, respectively. The highest number of lesions was recorded at 25 C for 72 h and the lowest at 10 and 30 C. The angular transformation of the proportion of the maximum number of lesions for each repetition was related to centered temperature and leaf wetness duration by a weighted least squares polynomial regression, (R²-adj. [adjusted] = 74.8%). Cluster analysis was used to divide the response surface into four disease-severity values. The shortest time interval from inoculation to the appearance of first lesions occurred under optimal conditions of temperature and leaf wetness duration.