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Tolerance of Verticillium malthousei to Benomyl. Paul J. Wuest, Associate Professor, Plant Pathology Extension, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Herbert Cole, Jr.(2), and Patricia L. Sanders(3). (2)(3)Professor, and Research Aide, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 64:331-334. Accepted for publication 4 September 1973. DOI: 10.1094/Phyto-64-331.

Three isolates of Verticillium malthousei, ML2, ML4, BC69, were evaluated for benomyl sensitivity. Isolate response in the presence of benomyl measured by linear growth, sporulation, and germinability of spores harvested from benomyl-amended plates of potato-dextrose agar was consistent. Isolate ML2 was benomyl-tolerant, whereas ML4 and BC69 were benomyl-sensitive. When Agaricus bisporus sporocarps were dipped into benomyl and inoculated with the isolates, results coincided with the three in vitro tests. However, ML2 was neither an aggressive nor virulent pathogen which suggests that this benomyl-tolerant isolate has little epidemiological significance. The 1958 collection date of ML2 is significant since it antecedes the introduction and use of benomyl. Since one isolate from the natural V. malthousei population was benomyl-tolerant, other benomyl tolerant isolates may be a threat to mushroom farms where Verticillium is controlled with benomyl.