ARE CLASSIFICATION AND PHYTOPATHOLOGICAL DIVERSITY COMPATIBLE IN XANTHOMONAS

The genus Xanthomonas is characterized by its phytopathogenic diversit y and the host specificity of its members. In the past, the classifica tion of the members of this genus has been based primarily on the crit erion of host specificity. This has led to a classification system whi ch focused only on naming phytopathogenic variants on different hosts. Extensive taxonomic examination of Xanthomonas has shown that the phy topathogenic specialization of the bacteria is not correlated with the actual relationships within the genus. Based upon total genomic DNA h omology, the genus has been reclassified into 20 species. At present, non-pathogenic xanthomonads are frequently isolated from plant materia l. As these strains often cannot be classified to existing species, it becomes clear that the diversity of the genus is much greater than ex pected from the phytopathogenic subpopulation, which has been the prim ary subject in the past. The example of Xanthomonas also illustrates t hat attempts to divide bacterial populations into discrete taxa confli ct with the actual continuous nature of biodiversity.