Systematic analysis of xanthomonads (Xanthomonas spp.) associated with pepper and tomato lesions

The taxonomy and evolutionary relationships among members of the genus Xant homonas associated with tomato and pepper have been a matter of considerabl e controversy since their original description in 1921. These bacteria, whi ch are a major affliction of tomato and pepper craps in warm and humid regi ons, were originally described as ii single species, but subsequent researc h has shown the existence of at least two genetic groups differentiated by physiological, biochemical and pathological characteristics. This work synt hesizes the findings from several approaches, including pathogenicity tests , enzymic activity, restriction fragment analysis of the entire genome, DNA -DNA hybridization and RNA sequence comparisons based on a 2097 base sequen ce comprising the 16S rRNA gene, the intergenic spacer located between the 16S and 23S rRNA genes and a small region of the 23S rRNA gene. Within the group of xanthomonads pathogenic on pepper and tomato four distinct phenoty pic groups exist, of which three form distinct genomic species. These inclu de Xanthomonas axonopodis pv. vesicatoria (A and C group), Xanthomonas vesi catoria (B group) and Xanthomonas gardneri (D group). On the basis of pheno typic and genotypic differences between A- and C-group strains, the C strai ns should be considered as a subspecies within Xanthomonas axonopodis pv. v esicatoria.