Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/19/2006
Publication Date: 6/1/2006
Citation: Smilanick, J.L., Schmidt, L., Ghosph, J., Margosan, D.A. 2003. Mutation at beta-tubulin gene codon 200 of penicillium digitatum conferred thiabendazole resistance. Plant Disease. 90: 765-770. Interpretive Summary: Green mold of citrus, which causes significant economic losses annually for the citrus industry, is controlled by the fungicide thiabendazole whose effectiveness has declined as resistance to this fungicide by the green mold pathogen has developed. We surveyed and collected resistant mold strains from around California and found, although they differed from each in other ways, those resistant to this fungicide had all developed thiabendazole resistance to the same level and by the same mechanism. Our identification of the single mechanism and gene involved with resistance is an important step in the understanding and management of this problem, and facilitates the development of tools such as molecular probes, that could rapidly detect resistant strains from among molds collected in groves or pacinghouses.
Technical Abstract: Penicillium digitatum, cause of citrus green mold, was isolated from infected lemons and oranges from many diverse locations in California. Those from groves, with no history of fungicide use, were sensitive to thiabendazole (TBZ), while those collected from ten citrus packinghouses were often TBZ resistant. RAPD analysis indicated both resistant and sensitive isolates collected were unique individuals. All twenty TBZ resistant isolates of P. digitatum characterized displayed a point mutation in the beta-tubulin gene sequence relating to amino acid codon position 200. Thymine was replaced by adenine (TTC to TAC), which changed the phenylalanine (F) to tyrosine (Y). In contrast, forty-nine TBZ sensitive isolates were sequenced and had no mutations at this or any other codon positions and their amino acid sequences were identical.