VIEW ARTICLE

Physiology and Biochemistry

The Significance of Tomatine in the Host Response of Susceptible and Resistant Tomato Isolines Infected with Two Races of Fusarium oxysporum f. sp. lycopersici. C. A. Smith, Graduate research assistant, Department of Botany and Plant Pathology, University of New Hampshire, Durham 03824, Present address of senior author: Department of Plant Pathology, University of Kentucky, Lexington 40546; W. E. MacHardy, associate professor, Department of Botany and Plant Pathology, University of New Hampshire, Durham 03824. Phytopathology 72:415-419. Accepted for publication 29 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-415.

Tomatine concentrations in the xylem fluid of Improved Pearson (IP) and Pearson VF-11 (VF) near-isolines of tomato were compared following wounding or wounding and inoculating with Fusarium oxysporum f. sp. lycopersici race 1 or race 2. VF is resistant to race 1 but susceptible to race 2; IP is susceptible to both races. Tomatine levels were similar in both isolines prior to treatment. Tomatine remained at the pretreatment level (3 × 10^–4 M) in the IP plants regardless of treatment, but increased to fungitoxic levels (10^–3 M) 2 days after wounding or inoculation in both the resistant VF/race 1 and susceptible VF/race 2 combinations. Tomatine in vitro was inhibitory to the vegetative growth of both races. Tomatine stimulated spore production of both races. The data suggest that tomatine is not a primary determinant of resistance to F. oxysporum f. sp. lycopersici. The possible role of tomatine in a sequential resistance process involving physical localization responses is discussed.