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Disease Control and Pest Management

Acid Production, a Possible Basis for Benomyl Tolerance in Verticillium malthousei. D. H. Lambert, Graduate Assistant, Department of Plant Pathology, 211 Buckhout Laboratory, The Pennsylvania State University, University Park 16802; P. J. Wuest, Professor, Department of Plant Pathology, 211 Buckhout Laboratory, The Pennsylvania State University, University Park 16802. Phytopathology 66:1144-1147. Accepted for publication 23 January 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1144.

Benomyl tolerance for 12 strains of Verticillium malthousei was associated closely with ability to produce acid; e.g., for supplemented Czapek Dox broths, the pH’s of culture filtrates of tolerant strains ranged from 3.5 to 5.4 vs. 6.2 to 7.4 for culture filtrates of sensitive strains. Benomyl effectiveness also was altered by buffering of media to differing pH. These results suggest that for this species, benomyl tolerance is not related directly to the fungicide’s mode of action, but may result partially or entirely from an alteration in fungal metabolism that conditions decreased sensitivity to benomyl, possibly by a pH-regulated reduction in uptake or binding.