Copper is widely used for control of plant pathogenic bacteria including Pseudomonas syringae pv actinidiae (Psa), the causal agent of bacterial canker of kiwifruit. The main risk associated with the use of copper is that the pathogen becomes resistant to it. Copper-resistant strains are usually identified by their ability to grow on agar plates supplemented with different concentrations of copper. However, the ability to grow on a medium supplemented with copper and the concentration of copper to which bacterial strains are resistant depends on the composition of the medium used for the test. In addition, resistance to copper in the laboratory does not always correlate with a loss of control of that same pathogen in the field. To establish a correlation between ability to grow on plant treated with copper and ability to grow in presence of copper in the laboratory, different growing agar media have been modified and the growth of Psa on kiwifruit leaves treated with different level of copper has been followed. Strains of Psa which can grow in presence of copper concentrations which would otherwise be lethal have been isolated. The genetic basis for this ability has been found to be similar to that found in other bacteria (presence of genes from the pco and cus operons). Psa most probably acquired them by horizontal gene transfer from bacteria of the kiwifruit phylloplane. Some of these bacteria might also affect the ability of Psa to cause disease by interfering with bacterial communication. To understand better how copper influence those two mechanisms (acquisition of copper resistance genes and increased or decreased virulence), the effect of copper on the epiphytic microbiome of the kiwifruit leaf is being investigated. The effect of copper is being assessed using Illumina Miseq Sequencing using the V5V6 region of the ribosomal DNA as barcode.