VIEW ARTICLE

Ecology and Epidemiology

Effects of Relative Humidity on Bacterial Scab Caused by Xanthomonas campestris pv. vesicatoria on Pepper. S. Diab, Research assistant, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76 100, Israel; Y. Bashan(2), Y. Okon(3), and Y. Henis(4). (2)(3)(4)Instructor, senior lecturer and professor, respectively, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76 100, Israel; (2)Present address: Division of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. Phytopathology 72:1257-1260. Accepted for publication 25 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1257.

Differences in relative humidity (RH) significantly affected bacterial scab (leaf spot) development in pepper plants. High RH with free moisture on the leaves for long periods favored infection. However, Xanthomonas campestris pv. vesicatoria had modest requirements for high RH in order to cause disease. When inoculated plants were exposed to high RH (>85%) for a few hours during 1 or 2 days, the pathogen could cause disease symptoms. Short periods of unfavorably low RH after inoculation with the pathogen temporarily prevented disease development, but it continued later when high RH conditions were provided. Long periods at low RH irreversibly prevented the pathogen from initiating disease, even if high RH was provided later.