SCREENING FOR ERWINIA BILLINGIAE AND E. TASMANIENSIS IN FIELD ISOLATES, DIFFERENTIATION BY SEQUENCE ANALYSIS AND EFFECTS AS ANTAGONISTS

Epiphytic bacterial strains were isolated from the apple and pear phyllosphere in Australia, South Africa, Germany, England and Poland. Some of these carry genes with high homology to the ams cluster of Erwinia amylovora. In the center of this region resides wbdN, encoding for a glycosyl transferase. The wbdN gene probably substitutes amsE and is related in the genomes of Erwinia billingiae and Erwinia tasmaniensis. By sequence analysis of the 16S rRNA and the wbdN gene, similar strains were identified from South Africa and Europe and classified into the species E. tasmaniensis. The 16S rRNA sequences were almost identical for several levan-producing strains from Australia, South Africa and Germany. Three strains from Poland were classified as E. billingiae by blast searches with 16S rRNA sequences. A part of the wbdN gene within the EPS-encoding region was used to confirm the Polish isolates as E. billingiae and the others as E. tasmaniensis. The DNA fragment was identical for strains from Australia and comprised small changes characteristic for strains from South Africa and from Germany. This nucleotide sequence can differentiate the strains by the regions of their isolation. It can be assumed that strains of the species E. billingiae and E. tasmaniensis occur in many places worldwide and may also interfere with colonization of flowers of fire blight host plants by E. amylovora. Several isolates were screened for their ability to suppress growth of E. amylovora on plant tissue such as apple flowers or pear slices.