Pathogenic and molecular diversity of Ralstonia solanacearum isolates from the Brazilian Amazon.
The diversity among 70 isolates of Ralstonia solanacearum collected from tomato and other hosts in the Brazilian Amazon was evaluated. Firstly, the isolates were identified at the biovar level and their virulence assessed by inoculating seedlings of tomato, sweet pepper and Amazon chicory (Eryngium foetidum). Fifty-three isolates were identified as biovar 1, four as biovar N2 and 13 as biovar 3, therefore confirming the prevalence of biovar 1 associated with tomato in the North Region of Brazil. Cluster analysis of the isolates allowed their separation into different virulence classes. On tomato, 44.3% of them were highly virulent, 37.1% were moderately virulent and 18.6% were weakly virulent. On peppers, 20% of the isolates were highly virulent, 27.1% moderately virulent and 52.9% were weakly virulent. When inoculated on Amazon chicory, only the chicory isolate caused wilt, thus revealing an uncommon specificity for R. solanacearum. Forty-six isolates from tomato and 18 from ten other hosts, collected in flooded and non-flooded areas, were then compared by BOX-PCR. Genomic fingerprints were highly polymorphic. Five groups were identified, without any clear-cut correlations among them with host of origin, biovar, ecosystem or geographic origin. The isolate obtained from Eryngium foetidum was the most divergent, with only 6.4% similarity to the other isolates. The tomato isolates were separated into three groups. All four biovar N2 isolates were grouped together and separated from the isolates representing the other biovars present in the Amazon region.