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 bacte¬rial diseases in areas where hazelnut is cultivated. In this study, 19 Xa and 19 Xac strains isolated in Chile from hazelnut symp¬tomatic plants, were characterised through Rep-PCR analysis. Several Xa pathovar reference strains (e.g. celebensis, pruni, and juglandis) were used as controls, while X. axonopodis pv. vitians DISTAL 9081 was 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 correspond¬ing 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 cory¬lina 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 patho¬genic 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 epidemiolog¬ical role of multiple characterization of Xa strains is discussed.
This work was partially supported by the National Agency for Research and Development (ANID)/FONDECYT Posdoctorado/3180629 and by University of Bologna RFO funds, DISTAL.