Efficacy of different copper compounds in the control of Xanthomonas citri subsp. citri pathotypes A and A*

Citrus canker disease is one of the most devastating diseases that attacks citrus, especially limes in the Southern parts of Iran, and is caused by Xanthomonas citri subsp. citri (Xcc). The efficacy of several formulations of copper compounds including Bordeaux mixture, copper oxychloride and copper sulphate in controlling Xcc in Key lime was estimated in vitro and in planta using artificial inoculation. Specific primers were used to detect copper-resistant genes copA, copB and copL in 30 isolates of Xcc. The copA and copL genes were present in all isolates, and copB was detected only in 6 strains. In this study, we observed a very good in vitro growth inhibition activity of copper compounds against Xcc pathotype A. S14 strain (pathotype A^*) was the sole isolate that grew on media amended with 2/4 mM of Bordeaux mixture, copper oxychloride and copper sulphate. All other strains (pathotype A) failed to grow on media amended with this concentration. Bordeaux mixture exhibited high efficacy in controlling Xcc in both conditions. However, there were no significant differences in the efficacy of copper oxychloride and copper sulphate at 1.2 mM concentration in planta. A significantly minimum canker necrotic spot and highest disease control was achieved with Bordeaux mixture and copper oxychloride. There was a significant difference in disease severity of the type strain LMG9322 (pathotype A) and Xcc strain S14 (pathotype A^*). Our experiments showed that Bordeaux mixture exhibited satisfactory efficacy in controlling the causal agent of citrus canker.