The role of multifaceted characterization of Chilean Xanthomonas arboricola strains in the management of the hazelnut bacterial blight

The Xanthomonas arboricola (Xa) species has a high genetic variability and the pv. corylina (Xac) is the etiological agent of the bacterial blight of hazelnut which is one of the main bacterial diseases in areas where hazelnut is cultivated. In this study, 19 Xa and 19 Xac strains isolated in Chile from hazelnut symptomatic plants, were characterised through Rep-PCR analysis. Several Xa pathovar reference strains (e.g. celebensis, pruni and juglandis) were used as controls, while DISTAL 9081 strain of X. axonopodis pv. vitians were used as outgroup. Then, multiplex end-point PCR on T3SS/T3Es/T3SPs genes, Biolog GenIIITM analysis, hypersensitivity and pathogenicity tests were carried out. The UPGMA analysis of Rep-PCR data discriminated the 38 Xa strains in statistically significant groups corresponding to the relative pathovars: pruni, corylina, juglandis and celebensis. The Xac strains showed a high genetic variability (approx. 45%). Similarly, the Rep-PCR data of the Xa strains from symptomatic shoots, leaves, buds and fruits gave results with a similarity of 50% among strains included in the corylina pathovar. As for virulence genes, the presence of hpaA, hrpD5, hrpF and xopAQ was confirmed in all strains, while xopZ was absent. The HR on French bean resulted positive for all strains, and the selected Xa/Xac strains resulted pathogenic on hazelnut plants. Finally, most of metabolic activity confirmed the molecular characterization of Xac/Xa strains, pooled in the same group. Moreover, the Xa strains were here combined in a sub-group of the Xac cluster. The epidemiological role of multiple characterization of Xa strains is discussed