ETD

• bacteriophages
• biocontrol
• Dickeya oryzae
• foot rot
• genotypic characterization
• phage therapy
• phenotypic characterization
• rice

Dickeya oryzae is the causal agent of rice root rot, an emerging threat to rice food production, causing severe yield losses across Asian countries and in Italy. Management of bacterial plant diseases largely relies on standard agricultural practices and broad-spectrum antimicrobials, which can negatively affect non-target microorganisms and promote resistance, requiring alternative approaches. Phage therapy has gained renewed interest primarily for the treatment of bacterial infections in clinical and veterinary settings, while it is also increasingly studied as a biocontrol approach in agriculture. This study aimed to isolate and characterize bacteriophages targeting D. oryzae and explore their biocontrol potential through in vitro and in planta studies. Three novel bacteriophages were isolated from rice paddy field samples. Genome sequencing revealed that phages 2VC and 6RO are jumbo phages, representing a novel species and a novel genus, respectively. Subsequently, the host range of the phages was tested. All three phages exhibited species-specific host ranges, with phage 1RO infecting 16 of the 20 strains tested, while phages 2VC and 6RO showed narrower specificity. The lytic activity of phages, evaluated in 24-hour kinetic assays against planktonic D. oryzae DZ2Q, was strongly enhanced when combined into a phage cocktail. The cocktail’s biocontrol potential was assessed in a rice germination assay, demonstrating improved germination compared to untreated controls. Finally, the preliminary screening for phage resistance of a transposon mutant library suggests that phages 2VC and 6RO may exploit motility-associated structures as receptors, although further experimental validation is required. Collectively, these findings support the potential of bacteriophages as biocontrol agents for managing D. oryzae in agriculture.