SURVIVAL OF XANTHOMONAS-FRAGARIAE ON STRAWBERRY IN SUMMER NURSERIES IN FLORIDA DETECTED BY SPECIFIC PRIMERS AND NESTED POLYMERASE CHAIN-REACTION

Genomic DNA from strain XF1425 of Xanthomonas fragariae was amplified with primers RST2 and RST3 from the hrp-gene region of Xanthomonas cam pestris pv. vesicatoria. The polymerase chain reaction (PCR) product w as sequenced. Four primers were selected at sites unique to X. fragari ae, which were identified by comparison with the sequences of PCR prod ucts amplified by the same primers from DNA of three strains of X. cam pestris pv. vesicatoria. Three primers were specific for amplification of DNA from X. fragariae but not from strains of 16 pathovars of X. c ampestris or nonpathogenic xanthomonads from strawberry. Bacteria were detected at approximately 10(4) to 10(5) CFU/ml by a single round of PCR. A nested PCR technique enabled detection to approximately 18 cell s. Restriction endonuclease digestion patterns of the PCR product were unique to X. fragariae and confirmed amplification of DNA from the ta rget organism. Bacteria were detected from symptomatic and asymptomati c plant tissue by the nested technique. From strawberry plants inocula ted with a rifampicin-resistant strain of X. fragariae and planted in the field in Florida, bacteria were detected by nested PCR and by reco very onto media at 2-week intervals for 92 days after planting. Daught er plants of the inoculated plants were positive for X. fragariae by n ested PCR amplification, indicating that X. fragariae survived on plan ts in summer nurseries in Florida and was disseminated to daughter pla nts.