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Physiological Responses of Susceptible and Resistant Cucumber to Erwinia tracheiphila. Charles E. Main, Former Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27607; J. C. Walker, Professor Emeritus, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 61:518-522. Accepted for publication 25 November 1970. DOI: 10.1094/Phyto-61-518.

Bacteria multiplied rapidly in susceptible cucumber plants inoculated with Erwinia tracheiphila. Initial wilt of lower leaves occurred after 2 days. Histological examination showed that the bacteria migrated upward through the xylem of stem and petiole en masse, and plugging coincided with progressive wilt of adjacent leaves. Vascular deterioration was first seen 6 days after inoculation, by which time the plants were completely wilted. No wilt, plugging, or vascular deterioration were observed for resistant plants. Isolation assays demonstrated virulent bacteria in resistant plants for 10 days after inoculation, but the bacteria disappeared by the time the plants reached maturity. Transpiration decreased 1 day after initial wilt, and continued to decrease progressively as wilt developed. Respiration increased 2 days after wilt, and increased progressively for 10 days. Only slight and delayed transpiration and respiration responses occurred in resistant plants, which indicated limited multiplication. No evidence for pectolytic or cellulotytic enzyme production in vitro or in vivo was observed. Vascular plugging and wilt preceded physiological response and vascular deterioration; therefore, the primary wilting mechanism was considered to be bacterial plugging. Resistance was thought to involve a nutritional or bacterial inhibition principle that prevented continued multiplication and characteristic susceptible wilt symptoms.

Additional keywords: Cucumis sativus, bacterial wilt.