The host specificity of plant pathogenic bacterial strains is generally high and well characterised, and numerous pathovars have been defined in many species of these pathogens.
A pathovar is a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at the sub-specific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one or more plant hosts.
The Xanthomonas genus contains about 30 species pathogenic to over 400 different plants including many crops.