Effects of Relative Humidity on Bacterial Scab Caused byXanthomonas campestrispv.vesicatoriaon Pepper

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Abstract
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, X. 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.