Influence of amylovoran production on virulence of Erwinia amylovora and adifferent amylovoran structure in E-amylovora isolates from Rubus

The amylovoran structures of five Erwinia amylovora isolates from Malaceae sp. and four isolates from Rubus sp. host plants were fully established, ma inly by NMR. The structural data on one E. amylovora isolate from a Malacea e sp. host, which had been previously suggested by mass and NMR (Nimtz et a l., 1996), were completed. E. amylovora strains infective on Malaceae sp. h ost plants had an amylovoran composed of pentasaccharide and 30-40% hexasac charide repeating-substructures, whereas amylovoran from E. amylovora isola tes from Rubus sp. host plants had only the pentasaccharide substructures. On the other hand, the exopolysaccharide (EPS) production differed in wild- type E. amylovora strains. Data on in vitro amylovoran production per cell could account for the differences in aggressiveness found in E. amylovora s trains, as deduced from a pilot test with highly, moderately, and weakly ag gressive strains. This correlation was confirmed with several other wild-ty pe E. amylovora strains from different origin.