Isolation and characterization of bacteriophages infecting Pseudomonas syringae pv. syringae, and evaluating their biological control efficiency

Bacterial canker is one of the most devastating diseases on the stone fruit trees. This disease is caused by a gram-negative bacterium called Pseudomonas syringae pv. syringae. Consecutive use of antibiotics and copper compounds has caused the emergence of new resistance races. One of the most promising replacement compounds is the use of bacteriophages. In this research, 56 soil samples were collected from the suspected trees of having bacterial canker from northwestern of Iran. In order to check the presence of phage particles, double-layer soft-agar technique was used to purify individual phage plaques. A total of 75 phage isolates, all of which had clear plaques, were isolated from the samples, among them, five phages with the highest lysing capability were selected for electron microscopy and greenhouse studies. Among the selected phages, three phages showed morphological similarity to Myoviridae, Tectividae and Microviridae families. Although all five phages were effective in reducing the growth of bacterial population in liquid culture medium, significant differences were observed between them. The cocktail prepared from the mixture of five phages showed a much stronger effect than the individual phages. The results of the greenhouse tests showed that these phages effectively reduce the development of the pathogen inside the bean and can reduce the bacterial symptoms in the treated plant by 90%. The five isolated phages in this research showed acceptable results in the control of the agent of bacterial canker of the stone fruit trees in the laboratory and in greenhouse experiments, and their actual formulation is recommended at the regional level.