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Control of Leaf Spot Diseases of Alfalfa and Tomato with Applications of the Bacterial Predator Pseudomonas Strain 679-2. L. E. Casida, Jr., Professor, Department of Molecular and Cell Biology, The Pennsylvania State University, University Park 16802. F. L. Lukezic, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 76:1217-1220. Accepted for publication 27 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1217.

Pseudomonas strain 679-2 is a unique, highly competitive, nonobligate bacterial predator originally isolated from soil. Application of its cells to tomato and alfalfa provided a reduction in the severity of the leaf spot diseases caused by Alternaria solani, Pseudopeziza medicaginis, Phoma medicaginis, and Stemphylium botryosum. The treatment produced no adverse effects on the plants. Strain 679-2 produces a water-soluble compound that inhibited these fungi, but the role of the compound in the interaction was not determined. Application of a copper fungicide to the leaves with the bacteria did not interfere with activity of strain 679-2. Although strain 679-2 survived well on the leaves and in soil, it could be programmed by culture techniques for early mortality in order to reduce unwanted environmental exposure.