Design of a Bacteriophage-Based Product for Biocontrol of Fire Blight and Black Rot.

Controlling phytopathogenic bacteria is essential for safeguarding crops and minimizing economic losses in agriculture. Although chemical pesticides are effective, they have adverse effects on ecosystems, beneficial organisms such as pollinators, and natural pathogen predators, creating a need for sustainable alternatives. Bacteriophages ɸEF1 and ɸEF2 (infecting Erwinia amylovora, the fire blight pathogen), and ɸXF1 (targeting Xanthomonas campestris, the black rot pathogen) have shown promise as biocontrol agents in vitro and in vivo. However, to be effective in the field these phages must maintain infectivity during storage and environmental exposure. We evaluated their stability under varying pH, temperature, UV and sunlight conditions and assessed various photoprotective additives. The phages remained infectious for up to 3 months at 4°C and 20°C and pH 7-9, but were inactivated at pH 3 and 37°C. UV rapidly inactivated the phages, but their stability was significantly enhanced by adding photoprotectants like Amino 22% or CaCO3, particularly CaCO3 at 24%, which preserved infectivity for over 8 h. These photoprotectants also improved phage recovery from plant surfaces. We conclude that effective biocontrol formulations should contain ≥ 106 pfu/mL, maintain neutral pH, include 24% CaCO3, and allow room temperature storage. This study is among the first to demonstrate the long-term stability of phage-based formulations at room temperature, together with improved field persistence, supporting their potential use as biopesticides.