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., CuSO4) 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 f20-Xaj, f29-Xaj, and f30-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 f20-Xaj and f30-Xaj indicates that these phages belong to the Pradovirus genus. In the field, the cocktail of these bacteriophages showed similar effectivity to CuSO4 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 CuSO4 treatment. These results show that the use of bacteriophages can be an alternative to combat the symptoms of walnut blight caused by X. juglandis.

Draft Genome Sequence of Xanthomonas arboricola pv. juglandis J303, Isolated from Infected Walnut Trees in Southern Chile.

Here, we report the draft genome sequence of Xanthomonas arboricola pv. juglandis J303, isolated from infected walnut trees in southern Chile. The size of the genome is 5,066,424 bp with a G+C content of 65.4%. X. arboricola pv. juglandis J303 has several genes related to virulence, antibiotic resistance, and copper resistance.

Complete Genome Sequences of Lytic Bacteriophages of Xanthomonas arboricola pv. juglandis.

Three bacteriophages, f20-Xaj, f29-Xaj, and f30-Xaj, with lytic activity against Xanthomonas arboricola pv. juglandis were isolated from walnut trees (VIII Bío Bío Region, Chile). These lytic bacteriophages have double-stranded DNA (dsDNA) genomes of 43,851 bp, 41,865 bp, and 44,262 bp, respectively. These are the first described bacteriophages with lytic activity against X. arboricola pv. juglandis that can be utilized as biocontrol agents.