Open Collections

Abstract

Highbush blueberry production in Canada is impacted by bacterial blight caused by Pseudomonas syringae complex. The major disease symptoms include black lesions and blight on floral buds and stems, resulting in diminished new growth and reduced berry yield. Pseudomonas can survive on healthy and symptomatic plant tissues before entering the plant’s apoplast leading to infection. Copper-based chemical sprays are the main prevention methods for bacterial blight. However, chemical methods are detrimental to the environment and are becoming less effective due to bacterial adaptation. Bacteriophages (phages) pose a promising alternative treatment for managing bacterial blight in blueberry plants compared to traditional chemical-based methods. Phages are viruses that replicate within specific bacteria to initiate cell lysis. Phage application is promising due to the high specificity, self-limiting properties, and environmental safety. The objectives of this research were to: (1) isolate lytic phages from natural sources which have the ability to lyse stains of P. syringae; (2) characterize the isolated phages in response to their host range and environmental stability; (3) compile a phage cocktail that can effectively reduce the concentration of bacterial blight in detached leaves of blueberry plants. Sixty-one phages were isolated from the environment, with the vast majority isolated from sewage influents. Preliminary host range assessments against 20 virulent strains of P. syringae complex identified 13 promising phages. Subsequent evaluation showed an average latent period of 40 minutes with a burst size between 8 and 341 phages per bacterial cell. Ideal storage conditions were 4ºC and pH 8, with all phages showing deterioration when exposed to UV light. Cocktails composed of 5 phages were evaluated against virulent strains of P. syringae complex to determine effectiveness in supressing bacterial growth. Phage cocktails were applied to blueberry leaves inoculated with strains of P. syringae complex and observed over 15 days at 10ºC. The resulting bacterial concentrations were reduced in treatment groups after 12 hours until 15 days. The results of this study show bacteriophages can act as a promising biocontrol for preventing bacterial blight. Further in planta assays are required for the efficacy of these phages to suppress the bacteria on highbush blueberries.