The Xanthomonas genus has been subject of numerous taxonomic and phylogenetic studies and was first described as Bacterium vesicatorium as a pathogen of pepper and tomato in 1921.[1] Dowson [2] later reclassified the bacterium as Xanthomonas campestris and proposed the genus Xanthomonas.[3] Xanthomonas was first described as a monotypic genus and further research resulted in the division into two groups, A and B.[4][5] Later work using DNA:DNA hybridization has served as a framework for the general Xanthomonas species classification.[6][7] Other tools, including multilocus sequence analysis and amplified fragment-length polymorphism, have been used for classification within clades.[8][9] So while previous research has illustrated the complexity of the Xanthomonas genus, recent research appears to have resulted in a clearer picture. More recently, genome-wide analysis of multiple Xanthomonas strains mostly supports the previous phylogenies.[10]