A genomically unique lytic bacteriophage infecting Pseudomonas syringae pv. actinidiae

Bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) continues to be a major threat to kiwifruit production worldwide. Current control methods, focused on chemical treatments and orchard hygiene strategies have low efficacy and pose several limitations, necessitating novel sustainable alternatives. In this study, a new lytic Myovirus bacteriophage, Qdp_Psa3, was isolated and characterized from Psa infected kiwifruit orchard soil. The bacteriophage displayed a narrow host range across Psa biovars (1, 2, and 3), strong pH stability and moderate thermal stability being inhibited at temperatures above 25 °C. Genomic sequencing revealed a 115 kb dsDNA genome lacking antibiotic resistance, tRNA, or virulence genes, and the analysis of the DNA packaging cassette suggested an uncharacterized mechanism. Phylogenetic and comparative genomic analyses support its designation as a novel species within the Caudoviricetes class, with proteomic profiling identified 62 virion-associated proteins, 71% of which remains hypothetical. Qdp_Psa3 demonstrated potential as a biocontrol agent, representing a promising candidate for inclusion as a complementary bacteriophage in a phage cocktail. Its discovery provides valuable insights into the hidden viral diversity of kiwifruit soils and expands our understanding of bacteriophage-Psa interactions.