Abstract Clavibacter michiganensis subsp. michiganensis (Cmm), which is a Gram positive bacterium, causes the bacterial canker of tomato disease. The purpose of the study was to evaluate the antibacterial activity of Polygonum orientale extracts against Cmm. In this study, firstly, effects of three extracting parameters (extractive time, extractive temperature, and solid to liquid ratio) of orthogonal experiment design L27 (313) were conducted. Secondly, survival rate was determined and inhibition zone of Cmm rescued post-stress was monitored. Finally, extracellular OD260nm value, extracellular protein content, conformational structure of membrane protein, extracellular alkaline phosphatase (AKP) activity, and ATPase activity were measured to investigate the antibacterial mechanism. Results of orthogonal experiment revealed that extractive time and extractive temperature had highly significant (P<0.01) effects on the antibacterial activity of P. orientale extracts.

The optimum conditions were as follows:

10h of extractive time, 60°C of extractive temperature, and 1:20 (g:mL) of solid to liquid ratio. This study also demonstrated that the living cells of each sample from survival rate test had almost no resistance or adaptability, and rescued Cmm cells were much easier to be inhibited by P. orientale extracts. The results of antibacterial mechanism indicated that cell membrane and cell wall of Cmm were seriously damaged by P. orientale extracts, and P. orientale extracts reduced the intracellular ATPase activity dramatically. All these findings suggested that P. orientale extracts had a strong antibacterial activity to inhibit Cmm, and could be used for the ecological management of the bacterial canker of tomato disease.