Abstract Background The control of Clavibacter michiganensis , the causal agent of bacterial canker in tomato, remains a significant challenge for crop cultivation. While copper‐based products are the most commonly used bactericides, their efficacy against this pathogen is often inefficient. Therefore, the objective of this study was to determine the copper susceptibility of five Chilean Clavibacter michiganensis strains and to characterize their associated copper resistance gene repertoire. Results Chilean strains VQ28, VQ143, and VL527 showed moderate copper resistance, being able to grow at a concentration ≤ 0.32 m m of copper in CYEG medium. In contrast, strains OP3 and MSF322 showed higher copper resistance, growing at a copper‐concentration ≤ 0.4 m m . The search for genes associated with copper resistance revealed the presence of the copA, copC, copD, copZ, ycnI and ycnJ genes and the csoR1 regulator gene in the chromosomes of all the strains analyzed. The presence and location of the csoR2 and csoR3 regulators genes varied among the strains. Strains MSF322 and OP3, shown to be more tolerant to copper, possess a copB gene located in a plasmid which was not found in other Chilean strains. Notably, strain OP3, isolated in 2015 – years after the other strains – harbors copper resistance genes on plasmids highly similar to those in other Chilean strains, suggesting recent horizontal gene transfer. Conclusion Chilean strains of Clavibacter michiganensis exhibit moderate tolerance to copper, and the acquisition of new genes through horizontal gene transfer could play a crucial role in Clavibacter michiganensis copper resistance. © 2026 Society of Chemical Industry.
Valenzuela et al. (Sat,) studied this question.