Abstract:
Forty-four bacteriophage isolates of Erwinia amy/ovora, the causal agent of fire
blight, were collected from sites in and around the Niagara Region of Southern Ontario
in the summer of 1998. Phages were isolated only from sites where fire blight was
present. Thirty-seven of these phages were isolated from the soil surrounding infected
trees, with the remainder isolated from aerial plant tissue samples. A mixture of six E.
amy/ovora bacterial host strains was used to enrich field samples in order to avoid the
selection bias of a single-host system. Molecular characterization of the phages with a
combination of peR and restriction endonuclease digestions showed that six distinct
phage types were isolated. Ten phage isolates related to the previously characterized
E. amy/ovora phage PEa1 were isolated, with some divergence of molecular markers
between phages isolated from different sites. The host ranges of the phages revealed
that certain types were unable to efficiently lyse some E. amy/ovora strains, and that
some types were able to lyse the epiphytic bacterium Pantoea agg/omerans. Biological
control of E. amy/ovora by the bacteriophages was assessed in a bioassay using discs
of immature pear fruit. Twenty-three phage isolates were able to significantly suppress
the incidence of bacterial exudate on the pear disc surface. Quantification of the
bacterial population remaining on the disc surface indicated that population reductions
of up to 97% were obtainable by phage treatment, but that elimination of bacteria from
the surface was not possible with this model system.
