VIEW ARTICLE

Ecology and Epidemiology

Effect of Temperature and Relative Humidity on the Latent Period of Venturia inaequalis in Apple Leaves. J. R. Tomerlin, Research associate, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824, Present address of senior author: Field Crops Laboratory, Plant Genetics and Germplasm Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; A. L. Jones, professor, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. Phytopathology 73:51-54. Accepted for publication 20 May 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-51.

The latent period for Venturia inaequalis was longer in leaves of McIntosh apple seedlings kept at 10 C than at 15 or 20 C in growth chambers. Latent periods were similar on seedlings kept at 15 or 20 C. Latent periods on seedlings kept at 20 or 10 C for 5 days, then at 10 or 20 C, were the same as those on seedlings kept continuously at 20 C. Latent periods on seedlings kept at low relative humidity (RH) (<70%) up to 6 days then at high RH (>70%), were similar to those for seedlings kept continuously at high RH. Lesions failed to develop on inoculated seedlings kept at low RH for up to 30 days, or on those kept at low RH after 3 or 6 days at high RH. Lesions developed on seedlings transferred to high RH after being maintained at low RH for 10- 24 days, although latent periods were 4- 16 days longer than on seedlings kept continuously at high RH. Latent periods on inoculated trees in the field often were longer than those reported by W. D. Mills. Regression analysis indicated that the duration of the latent period was related to both temperature and RH.