Biodegradation of Juglone by <i>Xanthomonas arboricola</i> pv. <i>juglandis</i>, the Causal Agent of Walnut (<i>Juglans regia</i> L.) Bacterial Blight

Xanthomonas arboricola pv. juglandis is the causal agent of walnut blight, a disease affecting Juglans regia L. cultivations by causing severe economic losses worldwide. The content of phenolic compounds in J. regia cultivars plays an important role in determining the resistance or susceptibility to the infection. In this study, the assessment of antimicrobial activity against several phytopathogenic X. arboricola and Pseudomonas strains revealed that X. a. pv. juglandis was less susceptible to juglone at higher concentrations, suggesting a potential resistance mechanism. To explore the antibacterial results, the biodegradation of juglone in the presence of X. a. pvs. juglandis and pruni were assessed at three different collecting times by NMR. The NMR analysis clearly showed the ability of X. a pv. juglandis NCPPB1659 to degrade juglone. On the contrary, X. a. pv. pruni NCPPB2588 was ineffective. The seasonal variation of juglone collected in leaves and husks of walnuts was determined.