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Effect of Ethanol on the Accumulation of Antifungal Compounds and Resistance of Tomato to Fusarium oxysporum f. sp. lycopersici. Stephen J. Danko, Graduate teaching assistant, Oregon State University, Corvallis 97330, Present address of senior author: Department of Agricultural Biochemistry, University of Nebraska, Lincoln 68583; Malcolm E. Corden, professor, Oregon State University, Corvallis 97330. Phytopathology 74:1475-1479. Accepted for publication 7 August 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1475.

The application of 1.0% ethanol to the roots of wilt resistant tomato plants (cultivar Jefferson) negated the effect of the I-gene for resistance to race 1 of Fusarium oxysporum f. sp. lycopersici. Vascular discoloration and foliar symptoms developed in ethanol-treated, inoculated plants just as in a wilt-susceptible cultivar (Bonny Best). The pathogen population in the xylem of the Jefferson plants increased rapidly when ethanol was applied, but remained low in inoculated, untreated plants. The antifungal activity of acetone extracts from the xylem of inoculated, ethanol-treated Jefferson plants remained low as it did in tomato plants of the same cultivar inoculated with race 2 of the pathogen, a race to which Jefferson plants are susceptible. By day 5 after inoculation, the fungitoxicity of xylem extracts was low in ethanol-treated plants inoculated with race 1 of the pathogen and in untreated plants inoculated with race 2, but was high in untreated, Jefferson plants inoculated with race 1. In vitro, ethanol neither stimulated nor acted as a substrate for ethylene biosynthesis by the pathogen, indicating that ethanol probably does not negate resistance through increased ethylene production by the pathogen. The fact that ethanol treatments that negate the resistance conferred by the I-gene also prevent the increase in antifungal compounds in the xylem supports the hypothesis that these antifungal compounds contribute to wilt disease resistance in tomato.

Additional keywords: Lycopersicon esculentum, phytoalexin theory.