Polyphasic characterization of Xanthomonas strains isolated from hazelnut symptomatic plants

The Xanthomonas arboricola (Xa) species has a high genetic variability and, among the 9 pathovars, pv. corylina causes the bacterial blight of hazelnut which is one of the main bacterial diseases present in all areas where hazelnut is cultivated. In this study, 19 Xa and 21 X. arboricola pv. corylina (Xac) strains isolated in Chile from European hazelnut symptomatic plants, were characterised through Rep-PCR analysis, where 13 X. arboricola reference strains belonging to the pathovars celebensis, pruni, juglandis and populi were used as controls, while DISTAL 9081 strain of X. axonopodis pv. vitians as outgroup; then, Biolog analysis, bioassays (hypersensitive response) and pathogenicity tests were carried out. The UPGMA cluster analysis of Rep-PCR fingerprints discriminated the 51 X. arboricola strains into 5 statistically significant groups corresponding to the relative pathovars: pruni, corylina, juglandis, celebensis and populi. The X. arboricola pv. corylina strains showed a high genetic variability (approx. 45%); similarly, the Rep-PCR fingerprints of the X. arboricola strains isolated from symptomatic hazelnut shoots and leaves gave similar results with a similarity value of approx. 50% among strains which were included in the corylina pathovar. The hypersensitive response on French bean resulted positive for all Xa/Xac strains, and the selected Xa/Xac strains resulted pathogenic on hazelnut plants confirming the Koch postulates. At last, most of metabolic activity data obtained with Biolog GenIIITM analysis confirmed the molecular characterization of Xac strains, pooled in the same group. Furthermore, the Xa isolates were here combined in a sub-group of the Xac cluster.