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Genetics

Resistance to Benomyl Conferred by Mutations in Codon 198 or 200 of the Beta-Tubulin Gene of Neurospora crassa and Sensitivity to Diethofencarb Conferred by Codon 198. Harrie Koenraadt, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824-1312; A. L. Jones, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824-1312. Phytopathology 83:850-854. Accepted for publication 18 March 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-850.

In previous work, we established that point mutations in codon 200 (200^{Phe to Tyr}) or 198 (198^{Glu to Ala}) of the beta-tubulin gene were associated with medium and very high resistance to benomyl in field strains of several plant-pathogenic fungi. Site-directed mutagenesis was performed to introduce identical mutations in codon 198 or 200 of a beta-tubulin gene from Neurospora crassa. At position 198 a codon for glutamic acid was altered to a codon for alanine. Alternatively, at position 200 a codon for phenylalanine was altered to a codon for tyrosine. Transformants were obtained that exhibited resistance to benomyl after transformation with plasmid constructs. Southern analysis confirmed that additional copies of beta-tubulin DNA were present in the transformants. Transformants with beta-tubulin DNA that were integrated with the codon for alanine also exhibited sensitivity to diethofencarb. Therefore, we conclude that mutations in codon 198 or 200 of the beta-tubulin gene confer resistance to benomyl in several benomyl-resistant plant-pathogenic fungi, as demonstrated in this study for N. crassa, and that an alanine codon at position 198 is associated with sensitivity to diethofencarb.