Description of copper tolerantXanthomonas citrisubsp.citriand genotypic comparison with sensitive and resistant strains

Abstract

The copper‐based products widely used for control of citrus canker may lead to the development ofXanthomonas citrisubsp.citri(X. citri) resistant to copper (CuR). However, the study of copper sensitivity ofX. citristrains from Paraná state, Brazil, did not reveal the existence of CuR, but copper tolerant (CuT) strains. The aim of this study was to describe for the first time the existence of CuTX. citriand compare the genetic determinants that differentiate the CuTstrains from the sensitive (CuS) and CuRstrains. CuTstrains supported intermediate concentrations of copper in comparison to CuSand CuR. CuTstrains lack the gene clusterscopLABorcopABCDresponsible for copper resistance in CuRstrains and the large plasmids (c. ≥200 kb) that normally carry these genes. The nucleotide sequences of chromosomal homologous genescohLAB, involved in copper homeostasis, were 100% similar in strains of all phenotypes. CuTstrains differed from CuSstrains by the higher expression of the homologous chromosomal genescohAandcohBin the presence of copper. CuTX. citristrains are not precursors of CuRstrains and do not pose a threat to the efficient use of copper‐based bactericides for management of citrus canker in citrus orchards. Copper resistance and tolerance are distinct phenotypes and should not be used as synonyms. The proper characterization of the sensitivity to copper leads to a more confident monitoring of the distribution of copper resistant populations ofX. citriand adoption of containment measures only when necessary.