Influence of amylovoran production on virulence of Erwinia amylovora and a different 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, mainly by NMR. The structural data on one E. amylovora isolate from a Malaceae sp. host, which had been previously suggested by mass and NMR (Nimtz et al., 1996), were completed. E. amylovora strains infective on Malaceae sp. host plants had an amylovoran composed of pentasaccharide and 30–40% hexasaccharide repeating-substructures, whereas amylovoran from E. amylovora isolates 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 strains, as deduced from a pilot test with highly, moderately, and weakly aggressive strains. This correlation was confirmed with several other wild-type E. amylovora strains from different origin.