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Sensitization of Leaves and Pathogens to Cold. C. E. Yarwood, Professor Emeritus of Plant Pathology, University of California, Berkeley, CA 94720; Phytopathology 67:855-858. Accepted for publication 20 January 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-855.

When healthy or diseased leaves were exposed to 0 C for 1 sec after a sublethal dosage of heat, the injury or therapy was usually greater than when the tissue was not chilled. Cold alone was not injurious or therapeutic at the dosages used. The sensitization of bean, corn, cowpea, cucumber, and thistle to cold was greater if the plants were held in darkness or grown at high temperature before the heat and cold treatment. The greatest sensitization to cold was with infections of Puccinia pelargoni-zonale in Pelargonium hortorum for which the dosage of heat for therapy was 12 times as great for heat alone (72 sec at 45 C) as for heat followed by cold (6 sec at 45 C). Sensitization to cold also was demonstrated for Puccinia antirrhini in snapdragon, Uromyces fabae in broad bean, Uromyces phaseoli in French bean, Pseudoperonospora cubensis in cucumber, and tobacco necrosis virus infection in cucumber and cowpea. No sensitization to cold was detected with two viruses, three powdery mildews, two aphids, or one mite. With Thielaviopsis basicola in carrot slices, chilling of tissues after heating reduced the therapeutic effect.

Additional keywords: Puccinia pelargonia-zonale, heat injury, heat therapy, cold therapy.