Synthesis and in planta antibacterial activity of head-to-head bis-benzimidazole and bis-benzoxazole derivatives

A series of head-to-head bis-benzimidazole and bis-benzoxazole derivatives was synthetized. Their antibacterial activity was examined in planta against Pseudomonas syringae pv. tabaci, the causal agent of wild fire in tobacco and in vitro against Pseudomonas syringae pv. tabaci and Pseudomonas syringae pv. tabaci. All synthetized compounds did not inhibit bacterial growth in vitro. However, they protected Nicotiana benthamiana against P. syringae pv. tabaci in the greenhouse. Only one foliar application at 50 mu g ml(-1) reduced diameter of leaf lesion by 25 to 52% as well as bacterial population in planta by 0.4 to 0.9 logarithmic units. This protection was associated with the inhibition of the accumulation of H2O2 in planta and enhancement of the activity of catalase, ascorbate peroxidase and guaiacol peroxidase. These results suggest that the bis-benzoimidazole and bis-benzoxazole derivatives act as antioxidants and may be used to protect plants against bacterial diseases.