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Benzimidazole-Resistant Mutant Derived from a Single Ascospore Culture of Botryotinia fuckeliana. F. J. Polach, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; W. T. Molin, Research Assistant, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 65:902-904. Accepted for publication 18 March 1975. DOI: 10.1094/Phyto-65-902.

A benomyl-resistant mutant of Botrytis cinerea was obtained by plating conidia derived from single ascospore isolates of Botryotinia fuckeliana on PDA plates supplemented with 10 µg/ml benomyl. Fifty percent reduction in linear mycelial growth of the wild-type and benomyl-resistant isolates occurred at 0.05 to 0.10 and 350 µg/ml benomyl, respectively. Some growth and limited sporulation of the resistant isolate occurred even at 1,000 µg/ml benomyl, the highest level tested. The resistant isolate produced conidia at all levels of benomyl tested and consistently sporulated more profusely than the sensitive isolate. Germination of conidia produced on 1,000 µg/ml benomyl was almost 100% on water agar, and 98% of these conidia formed colonies and subsequently sporulated when transferred from water agar to 500 µg/ml benomyl. The resistant isolate was also resistant to other benzimidazole fungicides tested, whereas both benomyl-resistant and benomyl-sensitive isolates were sensitive to dichloran. Both resistant and sensitive isolates were pathogenic on bean leaves and pods, although the sensitive isolate was slightly more aggressive.