Bacteriophage Cocktail Comprising Fifi044 and Fifi318 for Biocontrol of Erwinia amylovora

Erwinia amylovora is a plant pathogen that causes fire blight on apples and pears. Bacteriophages, which are viruses that selectively infect specific species of bacteria and are harmless to animal cells, have been considered as biological control agents for the prevention of bacterial pathogens. In this study, we aimed to use bacteriophages that infect E. amylovora as biocontrol agents against fire blight. We isolated bacteriophages Fifi044 and Fifi318 infecting E. amylovora, and characterized their morphology, plaque form, and genetic diversity to use as cocktails for disease control. The stabilities of the two phages were investigated at various temperatures and pH values and under sunlight, and long-term storage experiment was conducted for a year. To evaluate whether the two phages were suitable for use in cocktail form, growth curves of E. amylovora were prepared after treating the bacterial cells with single phages and a phage cocktail. In addition, a disease control test was conducted using immature apples and in vitro cultured apple plantlets to determine the biocontrol effects of the phage cocktail. The two phages were morphologically and genetically different, and highly stable up to 50°C and pH value from 4 to 10. The phages showed synergistic effect when used as a cocktail in the inhibition of host bacterial growth and the disease control. This study demonstrated that the potential of the phage cocktail as a biocontrol agent for commercial use.