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Identification of Pseudomonas syringae pv. phaseolicola by a DNA Hybridization Probe. N. W. Schaad, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83843, Present address: Harris Moran Seed Co., 100 Breen Rd., San Juan Bautista, CA 95045; H. Azad(2), R. C. Peet(3), and N. J. Panopoulos(4). (2)Department of Plant Pathology, University of California, Berkeley 94720, Present address: Department of Plant Pathology, University of California, Riverside 92521; (3)Department of Plant Pathology, University of California, Berkeley 94720, Present address: Zoecon Research Institute, 975 California Ave., Palo Alto, CA 94304; (4)Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 79:903-907. Accepted for publication 30 January 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-903.

A ³²P-labeled DNA probe carrying a gene(s) involved in phaseolotoxin production by Pseudomonas syringae pv. phaseolicola was used to detect and identify P. s. phaseolicola in pure or mixed cultures, seed-soak liquids, and diseased specimens collected in the field. The probe hybridized with all 34 strains of P. s. phaseolicola tested. All interspecific (pathovar) or intergeneric hybridizations were negative. Hybridization tests were highly reliable for pathogen detection and identification when individual colonies of P. s. phaseolicola could be picked individually from seed-soak liquid assay plates or when maceration fluids from disease lesions were assayed. Probings of maceration fluids from disease lesions also were highly reliable. In contrast, soak liquids from seeds contaminated with P. s. phaseolicola or washings of colonies from agar plates of such liquids gave variable results.