IDENTIFICATION OF XANTHOMONAS-FRAGARIAE FIELD ISOLATES BY REP-PCR GENOMIC FINGERPRINTING

Xanthomonas fragariae, the causal organism of angular leaf spot on cul tivated strawberry (Fragaria x ananassa), is an economically important pathogen of nursery stock in California. The ability to reliably dete ct this pathogen in a timely manner is crucial for the production and timely distribution of disease-free nursery stock. Pathogenicity testi ng for this disease requires excessive time, and the bacterium grows s lowly on standard culture medium. A medium, similar to that used for c ulturing Xylella fastidiosa, allowed more consistent recovery of X. fr agariae ii-om infected strawberry plants. Using the polymerase chain r eaction (PCR) with primers that anneal to dispersed repetitive bacteri al sequences (rep-PCR), we generated genomic fingerprints of reference strains oi X. fragariae (ATCC 33239 and 33240). These fingerprints we re used, in turn, to accurately identify X. fragariae field isolates c ollected over the last 5 years from nurseries in California. The rep-P CR fingerprint results agree with pathogenicity test results, require much less time than the pathogenicity test, and have greater specifici ty 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. fragari ae and it constitutes a useful tool for the production of disease-free strawberry nursery stocks.