Caracterização polifásica e descrição de novas hospedeiras de isolados de Xanthomonas citri subsp. citri do Nordeste do Brasil

Abstract

Citrus canker is one of the main threats to citrus culture in Brazil. This disease is caused by the bacterium Xanthomonas citri subsp. citri, classified as a quarantine organism. In the Northeast this bacterium is little studied, increasing the concern due to its destructive potential. Therefore, this study aimed: (i) to assemble a collection of X. citri subsp. citri strains from Northeast Brazil; (ii) to investigate and report the existence of citrus canker in the state of Rio Grande do Norte; (iii) to characterize the genetic variability of X. citri subsp. citri strains obtained from Northeast Brazil through rep-PCR genotyping; (iv) to perform the molecular identification of these strains through multilocus sequence analysis (MLSA); (v) to characterize the strains using biochemical tests, using the Biolog® system; (vi) to carry out the pathological characterization using different citrus cultivars; (vii) to characterize the sensitivity of isolates of X. citri subsp. citri to copper-based bactericides and investigating the genes involved in resistance; (viii) to test the ability of plants not belonging to the Rutaceae family to serve as hosts for X. citri subsp. citri. A total of 143 strains were obtained from different areas and states of the Brazilian Northeast. Through MLSA analyses, was carried the first report of citrus canker in the state of Rio Grande do Norte. The combination of rep-PCR (REP, ERIC, and BOX), MLSA and Biolog confirms that the population of strains obtained has low genetic and biochemical variability, suggesting a genetic homogeneity among the strains present in the Northeast region. In addition, we confirmed the occurrence of citrus canker in the states of Ceará and Piauí. The Pathological characterization on different citrus cultivars indicate that all strains in our collection belong to pathotype A and, apparently, there are no subtypes of X. citri subsp. citri. Representative strains used in the in vitro sensitivity test show similar results in terms of sensitivity to copper hydroxide and copper oxychloride. Furthermore, CopA and CopB genes are not present in these strains, which apparently indicates the absence of copper-resistant strains. However, the copL gene was detected in all tested strains, but alone it does not confer copper resistance. Finally, was performed the first report of infection in Anacardium occidentale, Schinus terebinthifolia and Mangifera indica by X. citri subsp. citri, through artificial inoculation, suggesting that these plants can serve as alternative hosts for X. citri subsp. citri.