Xanthomonas arboricola pv. corylina, causal agent of hazelnut bacterial blight: phenotypic and genomic characteristics of Chilean strains

Nowadays, the worldwide most important disease affecting hazelnut trees is caused by the highly host specific Xanthomonas arboricola pv. corylina (Xac). In fact, bacterial blight of Corylus avellanae (BBCa) reduces the vigour mainly of young hazelnut plants with devastating damages and yield losses either in orchards or in nurseries where the negative consequences on production are even worse. Recently, first reports of BBCa in European countries are on the rise, and serious outbreaks have been detected in Serbia, Italy and Chile. The prevalence of BBCa in Chile and favourable environmental factors in commercial orchards and nurseries are only partially known. Since in Chile the knowledge on pathogenicity and epidemiology of Xac is poorly understood, Xac Chilean strains from European hazelnut symptomatic plants, either from both commercial orchards and nurseries, were characterized with polyphasic approach in order to develop an integrated Xac control strategy. As the Xac lies within the Xanthomonas arboricola (Xa) species, which has a high genetic variability and has been intensively studied because of its strain specialization and host range complexity, the metabolic activity of 21 Xac strains and 19 Xa was evaluated using a Biolog GenIIITM analysis. 13 out of 19 Xa 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. The phenotypic analysis confirmed the data obtained by Rep-PCR: a) Xac strains showed a high genetic variability (approx. 45%); b) the Rep-PCR fingerprints of the Xa 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. Bioassays (hypersensitive response) and pathogenicity tests were also carried out.