Zohreh Ebrahimi

As a consequence of the abundant use of copper bactericides, some species of plant pathogenic bacteria, including Xanthomonas citri pv. citri (Xcc), have developed resistance to copper. This study evaluates pathological phenotypes and in vitro efficiency of prevalent copper compounds in inhibiting Xcc. Sampling was conducted across citrus orchards during 2021-2022. One hundred and seventeen citrus orchards were surveyed and 132 strains identified as Xanthomonas citri pv. citri based on phenotypic and genotypic characteristics. Different pathogenic phenotypes were observed by inoculating the representative strains on different cultivars of lime, orange, citrumelo and grapefruit, but tangerine cultivars did not show disease symptoms. All the strains showed an intermediate level of sensitivity and grew in the medium containing 100 and 150 mg/l of copper sulfate. In addition higher concentrations (250, 300, 350 and 400 mg/liter) showed inhibition rate more than 90%. Copper carboxylate at the concentration of 0.75 g/liter prevented the growth of more than 85% of the strains. Also, Copper oxychloride showed the best inhibition rate in concentrations higher than 3 g/liter. 1.5 ml/liter of Bordeaux mixture controlled more than 80% of the strains. None of copper resistance gene clusters copLAB and copABCD were detected in tested Xanthomonas citri strains. The proper characterization of pathological phenotypes and sensitivity to copper leads more confident decisions in citrus canker disease management.