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Molecular Plant Pathology

Mutations Leading to Substitutions at Amino Acids 198 and 200 of Beta-Tubulin that Correlate with Benomyl-Resistance Phenotypes of Field Strains of Botrytis cinerea. Oded Yarden, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100; Talma Katan, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. Phytopathology 83:1478-1483. Accepted for publication 7 September 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1478.

Three phenotypes were identified among benomyl-resistant strains of Botrytis cinerea in Israel when tested for sensitivity to carbendazim (MBC) and diethofencarb (NPC): Ben^HRNPC^S = highly resistant to MBC (50% effective concentration [EC₅₀] > 50 µg/ml) and sensitive to 0.5 µg/ml NPC; Ben^MRNPC^R = moderately resistant to MBC (10 ? EC₅₀ < 20 μg/ml) and resistant to 10 µg/ml NPC; and Ben^HRNPC^R = highly resistant to MBC and resistant to NPC. A 1-kb fragment of the wild-type gene encoding for beta-tubulin (designated benA) in B. cinerea was cloned and sequenced. The deduced partial amino acid sequence of the B. cinerea beta-tubulin showed a high degree of similarity to beta-tubulins of other filamentous fungi. A polymerase chain reaction approach was used to amplify and sequence 992-bp benA fragments from strains representing the three phenotypes. In the eight Ben^R strains analyzed, three single base-pair mutations were identified and found to correlate with the different phenotypes: codon 198, encoding glutamic acid in the wild type, was changed to an alanine codon in the Ben^HRNPC^S phenotype or to a lysine codon in the Ben^HPNPC^R phenotype; codon 200, encoding phenylalanine, was changed to a tyrosine codon in the Ben^MRNPC^R phenotype. These mutations were similar to those identified in benomyl-resistant field strains of other phytopathogenic fungi.

Additional keywords: Botryotinia fuckeliana, fungicide resistance, gray mold, negative cross-resistance, N-phenylcarbamate.