Characterization of Xanthomonas citri sbsp. citri Strains, the Causal Agent of Citrus Canker

Abstract

Xanthomonas citri sbsp. citri (Xcc) is the bacterium that causes citrus canker, a disease restrictive for the international fresh fruit trade. In order to know its diversity, twenty Xcc isolates from Uruguay and the region, responsible for the most severe form of citrus canker, were studied for phenotypic and genotypic characterization. Its identity was confirmed by specific antibodies, PCR and inoculation. The virulence in grapefruit plants and the sensitivity to antibiotics were evaluated. At a genotypic level, the strains were characterized according to the plasmid profile and the repeated ERIC sequences. All the strains were resistant to streptomycin and ampicillin, strain 89.5ex was an exception, being resistant to ampicillin. The analysis of virulence, expressed by the number of induced pustules/cm2 of vegetal tissue, showed differences among the strains. However, it is not possible to group the isolates by the degree of similarity of the virulence. The 138.2 isolate stands out for the development of a greater number of pustules in all the assays. Three plasmid profiles were detected; the profile formed by two plasmids represented the majority, being present in 65% of the strains. The «fingerprint» obtained by ERIC is the same in 18 of the analysed isolates, even though two of them showed a differential band of 1992 bp. In spite of the differences mentioned, a high level of homogeneity was found in the population studied, a characteristic already described for Xcc. Interestingly, the most virulent isolate was the only one in which three plasmids were found.