Characterization of Xanthomonas arboricola pv. juglandis Bacteriophages against Bacterial Walnut Blight and Field Evaluation.

Xanthomonas arboricola pv. juglandis (hereafter X. juglandis ) is the etiological agent of walnut blight, the most important bacterial disease affecting walnut production worldwide. Currently, the disease is treated mainly with copper-derived compounds (e.g., CuSO 4 ) despite the evidence of genetic resistance in these strains. Regarding the effectiveness and sustainability, the use of a bacteriophage appears to be a biocontrol alternative to reduce X. juglandis load and symptomatology of walnut blight. Here, the phages f 20-Xaj, f 29-Xaj, and f 30-Xaj were characterized, and their effectiveness in walnut orchards against walnut blight was determined. These bacteriophages showed a specific lytic infection in X. juglandis strains isolated from Chile and France. Phylogenetic analysis of the complete genome of f 20-Xaj and f 30-Xaj indicates that these phages belong to the Pradovirus genus. In the field, the cocktail of these bacteriophages showed similar effectivity to CuSO 4 in the reduction of incidence and severity in walnut tissue. Moreover, the bacterial load of X. juglandis was significantly reduced in the presence of bacteriophages in contrast to a CuSO 4 treatment. These results show that the use of bacteriophages can be an alternative to combat the symptoms of walnut blight caused by X. juglandis .