Induction of defense-related enzymes in tomato (Solanum lycopersicum) plants treatedwith Bacillus subtilis CBR05 against Xanthomonas campestris pv. vesicatoria Running Head: B. subtilis CBR05 induced defense-related enzymes in tomato ABSTRACT Bacterial spot disease, caused by Xanthomonas campestris pv. vesicatoria is one of the most important destructive diseases of tomato in many parts of the agricultural world. Bacillus sp.has been reported to be significantly reducing the incidence of disease in the diversity of hosts. The present study aims to determine the effects of Bacillus subtilis CBR05 inoculation on bacterial spot disease severity and the induction of defense-related enzymes response in tomato. Tomato leaves were evaluated to determine the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO)) and the content of malondialdehyde (MDA). A reduction in bacterial spot severity was observed in plants inoculated with B. subtilis, compared those of uninoculated controls. A significant increase in SOD, CAT, POD, and PPO activities was observed in plants treated with B. subtilis after 24 h inoculation compared with non-inoculated pathogen control and mock-inoculated controls. During 72 h after inoculation, B. subtilis inoculated plants resulted in significant increase of SOD, POD and PPO activities comparing to non-inoculated pathogen control. We also observed that low levels of natural SOD, CAT, POD, and PPO activities in the mock-inoculated control. Moreover, MDA content was induced by pathogen infection, and its amount in B. subtilis inoculated plants was significantly lower than in pathogen control. Our results suggest that early increases in antioxidant enzymes and the reduction in MDA content with B. subtilis inoculation may play a pivotal role in mitigating oxidative stress thereby induced systemic resistance against bacterial spot disease in tomato.