Identification of Xanthomonas fragariae field isolates by rep-PCR genomic fingerprinting
Xanthomonas fragariae, the causal organism of angular leaf spot on cultivated strawberry (Fragaria x 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 ii-om 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 oi 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.