Xanthomonas axonopodis pv. dieffenbachiae strains represent three phylogenetic groups of uncertain phytopathological relevance

Xanthomonas axonopodis pv. dieffenbachia is the causal agent of Anthurium bacterial blight and an A2 quarantine organism in the EU. Based on partial sequences of housekeeping genes, Xanthomonas axonopodis pv. dieffenbachiae strains consist of three different groups that correlate with grouping according to their original host (Anthurium, Philodendron and Dieffenbachia). This reveals that the quarantine pathovar does not reflect a distinct genetic entity, and which can have consequences for the phytosanitary regulation. To further examine the phytopathological meaning of the three phylogenetic groups, representative isolates of each group were characterized on the basis of pathogenicity on four Araceae species (Anthurium, Philodendron, Dieffenbachia and Alocasia), and of Type Three Effector (T3E) gene content and sequences. Complex variations were found not only between but also within the three groups and probably Xanthomonas axonopodis pathogens on Araceae result from a coevolution of bacteria from three different phylogenetic backgrounds.
Key words: Xanthomonas, Araceae, T3E, phylogeny, pathogenicity.