Identification of Bacteriophages for Biocontrol of the Kiwifruit Canker Phytopathogen Pseudomonas syringae pv. actinidiae

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:named-content content-type="genus-species">Pseudomonas syringae</jats:named-content> pv. actinidiae is a reemerging pathogen which causes bacterial canker of kiwifruit ( <jats:named-content content-type="genus-species">Actinidia</jats:named-content> sp.). Since 2008, a global outbreak of <jats:named-content content-type="genus-species">P. syringae</jats:named-content> pv. actinidiae has occurred, and in 2010 this pathogen was detected in New Zealand. The economic impact and the development of resistance in <jats:named-content content-type="genus-species">P. syringae</jats:named-content> pv. actinidiae and other pathovars against antibiotics and copper sprays have led to a search for alternative management strategies. We isolated 275 phages, 258 of which were active against <jats:named-content content-type="genus-species">P. syringae</jats:named-content> pv. actinidiae. Extensive host range testing on <jats:named-content content-type="genus-species">P. syringae</jats:named-content> pv. actinidiae, other pseudomonads, and bacteria isolated from kiwifruit orchards showed that most phages have a narrow host range. Twenty-four were analyzed by electron microscopy, pulse-field gel electrophoresis, and restriction digestion. Their suitability for biocontrol was tested by assessing stability and the absence of lysogeny and transduction. A detailed host range was performed, phage-resistant bacteria were isolated, and resistance to other phages was examined. The phages belonged to the <jats:named-content content-type="genus-species">Caudovirales</jats:named-content> and were analyzed based on morphology and genome size, which showed them to be representatives of <jats:named-content content-type="genus-species">Myoviridae</jats:named-content> , <jats:named-content content-type="genus-species">Podoviridae</jats:named-content> , and <jats:named-content content-type="genus-species">Siphoviridae</jats:named-content> . Twenty-one <jats:named-content content-type="genus-species">Myoviridae</jats:named-content> members have similar morphologies and genome sizes yet differ in restriction patterns, host range, and resistance, indicating a closely related group. Nine of these <jats:named-content content-type="genus-species">Myoviridae</jats:named-content> members were sequenced, and each was unique. The most closely related sequenced phages were a group infecting <jats:named-content content-type="genus-species">Pseudomonas aeruginosa</jats:named-content> and characterized by phages JG004 and PAK_P1. In summary, this study reports the isolation and characterization of <jats:named-content content-type="genus-species">P. syringae</jats:named-content> pv. actinidiae phages and provides a framework for the intelligent formulation of phage biocontrol agents against kiwifruit bacterial canker. </jats:p>