Molecular Characterization and Taxonomic Assignment of Three Phage Isolates from a Collection Infecting Pseudomonas syringae pv. actinidiae and P. syringae pv. phaseolicola from Northern Italy

Bacterial kiwifruit vine disease (Pseudomonas syringae pv. actinidiae, Psa) and halo blight of
bean (P. syringae pv. phaseolicola, Pph) are routinely treated with copper, leading to environmental
pollution and bacterial copper resistance. An alternative sustainable control method could be based
on bacteriophages, as phage biocontrol offers high specificity and does not result in the spread of
toxic residues into the environment or the food chain. In this research, specific phages suitable for
phage-based biocontrol strategies effective against Psa and Pph were isolated and characterized.
In total, sixteen lytic Pph phage isolates and seven lytic Psa phage isolates were isolated from soil in
Piedmont and Veneto in northern Italy. Genome characterization of fifteen selected phages revealed
that the isolated Pph phages were highly similar and could be considered as isolates of a novel species,
whereas the isolated Psa phages grouped into four distinct clades, two of which represent putative
novel species. No lysogeny-, virulence- or toxin-related genes were found in four phages, making
them suitable for potential biocontrol purposes. A partial biological characterization including a
host range analysis was performed on a representative subset of these isolates. This analysis was a
prerequisite to assess their efficacy in greenhouse and in field trials, using different delivery strategies.