RIBOTYPING OF ERWINIA-CHRYSANTHEMI STRAINS IN RELATION TO THEIR PATHOGENIC AND GEOGRAPHIC-DISTRIBUTION

16S and 23S rRNAs from Escherichia coli were used to study the relatio nship among a representative collection of strains of Erwinia chrysant hemi differing in their original host and geographical origin. Pheneti c analysis of restriction fragment length polymorphisms allowed the di stribution of the studied strains into seven clusters. These clusters were similar to those obtained by cladistic methods and appeared to co rrelate well with the established pathovars and biovars but to a lesse r extent with geographical distribution. Except for two groups of stra ins defined as tropical and temperate isolates (clusters 3 and 4, resp ectively), our clustering correlated well with botanical classificatio ns of host plants. However, the rRNA groupings were shown to be more d iscriminative than biovar analysis. To assess the relationship between rRNA clusters and pathogenicity, 12 representative strains from diffe rent clusters were tested for pathogenicity on different plants. The t wo typical symptoms, maceration and wilting, were observed for these s trains. The occurrence of the tobacco hypersensitivity reaction for a subset of these strains is discussed in light of recent results concer ning the presence of an hrp gene. Considering symptom expression only, rather than the capacity for plant infection, strains from the same c luster were shown to induce similar symptoms in test plants. Thus, sin ce host specificity is still quite controversial, rRNA patterns may co nstitute a useful tool in taxonomic and epidemiological studies of Erw inia chrysanthemi species.