No abstract

Bacteriophages are viruses that specifically infect target bacteria. Recently, bacteriophages have been considered potential biological control agents for bacterial pathogens due to their host specificity. Pseudomonas syringae pv. actinidiae (Psa) is a reemerging pathogen that causes bacterial canker of kiwifruit (Actinidia sp.). The economic impact of this pest and the development of resistance to antibiotics and copper sprays in Psa and other pathovars have led to investigation of alternative management strategies. Phage therapy may be a useful alternative to conventional treatments for controlling Psa infections. Although the efficacy of bacteriophage φ6 was evaluated for the control of Psa, the characteristics of other DNA bacteriophages infecting Psa remain unclear. In this study, the PHB09 lytic bacteriophage specific to Psa was isolated from kiwifruit orchard soil. Extensive host range testing using Psa isolated from kiwifruit orchards and other Pseudomonas strains showed PHB09 has a narrow host range. It remained stable over a wide range of temperatures (4–50 °C) and pH values (pH 3–11) and maintained stability for 50 min under ultraviolet irradiation. Complete genome sequence analysis indicated PHB09 might belong to a new myovirus genus in Caudoviricetes. Its genome contains a total of 94,844 bp and 186 predicted genes associated with phage structure, packaging, host lysis, DNA manipulation, transcription, and additional functions. The isolation and identification of PHB09 enrich the research on Pseudomonas phages and provide a promising biocontrol agent against kiwifruit bacterial canker.

Bacterial leaf blight (BLB) and bacterial leaf streak (BLS)—caused by Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), respectively—are two major bacterial diseases that threaten the safe production of rice, one of the most important food crops. Bacteriophages are considered potential biocontrol agents against rice bacterial pathogens, due to their host specificity and environmental safety. It is common for BLB and BLS to occur together in fields, which highlights the need for broad‐spectrum phages capable of infecting both Xoo and Xoc. In this study, two lytic broad‐spectrum phages (pXoo2106 and pXoo2107) that can infect various strains of Xoo and Xoc were assessed. Both phages belong to the class Caudoviricetes and one of them to the family Autographiviridae, while the other belongs to an unclassified family. Two phages alone or combined in a phage cocktail could effectively inhibit Xoo and Xoc growth in vitro. In an in vivo biocontrol experiment, the phage cocktail reduced the total CFU and significantly eased the symptoms caused by Xoo or Xoc. Our results suggest that pXoo2106 and pXoo2107 have a broad‐spectrum host range targeting different X. oryzae strains, and have strong biocontrol potential in field applications against both BLB and BLS.