Identification of Xanthomonas fragariae Field Isolates by rep-PCR Genomic Fingerprinting. D. C. Opgenorth, California Department of Food and Agriculture, Sacramento 95814. C. D. Smart, Department of Plant Pathology, University of California, Davis 95616; F. J. Louws, M.S.U.-D.O.E. Plant Research Laboratory and NSF Center for Microbial Ecology, Michigan State University, East Lansing 48824; F. J. de Bruijn, M.S.U.-D.O.E. Plant Research Laboratory, NSF Center for Microbial Ecology and Department of Microbiology, Michigan State University, East Lansing 48824; and B. C. Kirkpatrick, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 80:868-873. Accepted for publication 16 April 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0868.

Xanthomonas fragariae, the causal organism of angular leaf spot on cultivated strawberry (Fragaria ?ananassa), is an economically important pathogen of nursery stock in California. The ability to reliably detect this pathogen in a timely manner is crucial for the production and timely distribution of disease-free nursery stock. Pathogenicity testing for this disease requires excessive time, and the bacterium grows slowly on standard culture medium. A medium, similar to that used for culturing Xylella fastidiosa, allowed more consistent recovery of X. fragariae from infected strawberry plants. Using the polymerase chain reaction (PCR) with primers that anneal to dispersed repetitive bacterial sequences (rep-PCR), we generated genomic fingerprints of reference strains of X fragariae (ATCC 33239 and 33240). These fingerprints were used, in turn, to accurately identify X. fragariae field isolates collected over the last 5 years from nurseries in California. The rep-PCR fingerprint results agree with pathogenicity test results, require much less time than the pathogenicity test, and have greater specificity than indirect enzyme-linked immunosorbent assay for identifying X. fragariae from field plants. For these reasons, rep-PCR is the fastest and most accurate method for the current identification of X. fragariae and it constitutes a useful tool for the production of disease-free strawberry nursery stocks.