Induction of defence-related enzymes and resistance by the plant activator acibenzolar-S-methyl in tomato seedlings against bacterial canker caused by Clavibacter michiganensis ssp michiganensis

Using tomato seedlings, the plant defence activator acibenzolar-S-methyl (benzo-[1,2,3]-thiadiazole-7-carbothioic acid-S-methyl ester, ASM; Bion 50 WG) was assayed for its ability to induce resistance against Clavibacter michiganensis ssp. michiganensis, the causal agent of bacterial canker of tomato. In ASM-pretreated plants, reduction in disease severity (up to 76.3%) was correlated with lower bacterial growth (up to 68.2% lower) during the time course of infection. To understand the possible mechanism of action of ASM, alterations in the activities of peroxidase (POX) and chitinase were assessed as markers of resistance. The enhanced resistance of ASM-treated plants was associated with significant increases in the activities of POX and chitinase.