Biological and Genetic Characterizations of a Novel Lytic Phi Fifi106 against Indigenous Erwinia amylovora and Evaluation of the Control of Fire Blight in Apple Plants

Erwinia amylovora is a devastating phytobacterium causing fire blight in the Rosaceae family. In this study, Phi Fifi106, isolated from pear orchard soil, was further purified and characterized, and its efficacy for the control of fire blight in apple plants was evaluated. Its genomic analysis revealed that it consisted of 84,405 bp and forty-six functional ORFs, without any genes encoding antibiotic resistance, virulence, and lysogenicity. The phage was classified into the genus Kolesnikvirus of the subfamily Ounavirinae. Phi Fifi106 specifically infected indigenous E. amylovora and E. pyrifoliae. The lytic activity of Phi Fifi106 was stable under temperature and pH ranges of 4-50 degrees C and 4-10, as well as the exposure to ultraviolet irradiation for 6 h. Phi Fifi106 had a latent period of 20 min and a burst size of 310 +/- 30 PFU/infected cell. Phi Fifi106 efficiently inhibited E. amylovora YKB 14808 at a multiplicity of infection (MOI) of 0.1 for 16 h. Finally, the pretreatment of Phi Fifi106 at an MOI of 1000 efficiently reduced disease incidence to 37.0% and disease severity to 0.4 in M9 apple plants. This study addressed the use of Phi Fifi106 as a novel, safe, efficient, and effective alternative to control fire blight in apple plants.