DIVERSITY AMONG XANTHOMONADS PATHOGENIC ON PEPPER AND TOMATO

Xanthomonas campestris pv. vesicatoria, causal agent of bacterial spot of tomato and pepper, had been considered for nearly 70 years to be a relatively homogeneous organism. However, in the past decade this bac terium was determined to be composed of two genetically and phenotypic ally distinct groups. The two groups, designated A and B, were disting uished based on amylolytic activity, expression of unique protein band s, reaction on differential hosts (tomato races T1 and T2), reaction p atterns with monoclonal antibodies, DNA restriction profiles, and DNA: DNA hybridization. The A and B groups were placed into X. axonopodis p v. vesicatoria and X. vesicatoria, respectively. A third group, design ated C, was pathogenically (race T3) and serologically distinct from A and B strains, and formed unique DNA restriction profiles. DNA:DNA hy bridization data suggest that C is distinct but related to A strains a nd may represent a subspecies of A. A final group, designated D, consi sted of X. gardneri, an organism identified in Yugoslavia in 1957, and also found in Costa Rica. Group D was determined to be genetically di stinct from strains within the other two groups; it represents a third Xanthomonas species pathogenic on tomato and pepper.