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Interaction of Pseudomonas syringae and Freezing in Bacterial Canker on Excised Peach Twigs. D. J. Weaver, Research Plant Pathologist, Federal Research, Science and Education Administration, U. S. Department of Agriculture, Southeastern Fruit and Tree Nut Laboratory, P.O. Box 87, Byron, GA 31008; Phytopathology 68:1460-1463. Accepted for publication 2 May 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1460.

A test tube incubation technique was used to study the effect of freezing on the development of bacterial canker symptoms in excised peach twigs. Bark cankers with a characteristic water-soaked appearance and “sour-sap” odor developed only on twigs that were frozen at –10 C after inoculation with Pseudomonas syringae and then incubated at 15 C; neither freezing nor inoculation alone produced cankers. A brown discoloration noted in the xylem of twigs after inoculation was not correlated with development of bark cankers. Twigs of eight peach cultivars were compared for susceptibility to bacterial canker, and significant differences were found among the cultivars. Longer cankers developed on twigs collected when trees were dormant rather than on twigs collected when the chilling requirement had been satisfied. These results confirm field observations that bacterial canker on peach twigs results from an interaction between infection by P. syringae and freeze injury.

Additional keywords: Peach tree short life, Prunus persica.