DETECTION OF PSEUDOMONAS-SYRINGAE PV MORSPRUNORUM ON CHERRIES IN MICHIGAN WITH A DNA HYBRIDIZATION PROBE

A PST-DNA probe, developed for differentiating Pseudomonas syringae pv. tomato from P. s. pv. syringae, hybridized with DNA extracted from P. s. pv. morsprunorum but weakly or not at all with DNA extracted from P. s. syringae. Purified DNA and DNA from colony blots of 18 strains of P. s. morsprunorum, including strains from England, Poland, South Africa, and the United States, hybridized with the radiolabeled probe, whereas 19 of 20 strains of P. s. syringae isolated from deciduous tree fruit crops did not hybridize or weakly hybridized with the probe. The detection limit for bacteria from pure culture was approximately 2.2 X 10(4) colony-forming units (cfu) per milliliter. DNA from P. s. morsprunorum extracted from lesions on fruit was detected by the probe, but DNA from lesions on leaves was not detected. The number of bacteria was 100-fold lower in effluent from leaves than from fruit. With field samples, identifications made with the probe were in general agreement with those made by standard biochemical and physiological techniques. EcoRI fragments of P. s. morsprunorum DNA exhibited restriction fragment length polymorphism when Southern blots were probed with the PST-DNA probe. The PST-DNA probe should aid in the rapid detection of P. s. morsprunorum.