The potential of bacteriophages to control Xanthomonas campestris pv. campestris at different stages of disease development. Issue 6 (27th January 2022) - Holtappels, Dominique
Summary: Xanthomonas campestris pv. campestris (Xcc) is a vascular pathogen that invades the xylem of Brassica crops. Current chemical and antibiotics‐based control measures for this bacterium are unsustainable and inefficient. After establishing a representative collection of Xcc strains, we isolated and characterized bacteriophages from two clades of phages to assess their potential in phage‐based biocontrol. The most promising phages, FoX2 and FoX6, specifically recognize (lipo) polysaccharides, associated with the wxc gene cluster, on the surface of the bacterial cell wall. Next, we determined and optimized the applicability of FoX2 and FoX6 in an array of complementary bioassays, ranging from seed decontamination to irrigation‐ and spray‐based applications. Here, an irrigation‐based application showed promising results. In a final proof‐of‐concept, a CaCl2 ‐formulated phage cocktail was shown to control the outbreak of Xcc in the open field. This comprehensive approach illustrates the potential of phage biocontrol of black rot disease in Brassica and serves as a reference for the broader implementation of phage biocontrol in integrated pest management strategies. Abstract : Xanthomonas is an important phytopathogenic bacterial species, causing losses in crop production. Controlling its infection is therefore essential for a sustainable agriculture. Here, we describe the in‐depth molecular characterization and implementation of bacteriophages within the framework of integrated pest management. We developed tailored bioassays and showed that our phages perform well during seed steeping and that they limit the effects of the bacterium on seedling germination significantly. In greenhouse conditions, one of our phages outperforms the other in an irrigation‐based bioassay, resulting in a full disease control. Additional spray applications also demonstrate the potential of our phage to be used in this setting. Finally, we could demonstrate that a formulation of two phages significantly impacts infection in field conditions.