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Resistance

Fungitoxicity of Xylem Extracts From Tomato Plants Resistant or Susceptible to Fusarium Wilt. Erik L. Stromberg, Graduate Teaching Assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; Malcolm E. Corden, Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331. Phytopathology 67:693-697. Accepted for publication 3 December 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-693.

Acetone extracts of xylem vessels in the stems of wilt-resistant (Jefferson) and -susceptible (Bonny Best) tomato cultivars contained fungitoxic materials at concentrations that suppressed the growth of Fusarium oxysporum f. sp. lycopersici race 1 in vivo. Following inoculations in which spores of the pathogen were distributed throughout the major vessels of the stem, the population of viable fungal cells in both tomato cultivars rapidly decreased. In the susceptible cultivar, about 3 days after inoculation, the fungal population began to increase, while the fungitoxicity of the xylem extract decreased. In the resistant cultivar during this period, the Fusarium population remained low and the xylem extracts became highly fungitoxic. The fungitoxic material persisted in the resistant cultivar at a level that suppressed the growth of the pathogen; it may, in part, have been responsible for containment of the pathogen and thereby contributed to wilt resistance in tomato. In stems of noninoculated control plants, a high bacterial population developed that can confound many experiments with this disease.