Duality of acibenzolar-S-methyl in the inhibition of pathogen growth and induction of resistance during the interaction tomato/vertcillium dahliae

The plant defense activator, acibenzolar-S-methyl (ASM) was tested for its ability to protect tomato seedlings against verticillium wilt caused by Verticillium dahliae. ASM exhibited in vitro an antifungal activity in dose-dependent manner against three strains of the pathogen with the less virulent strain SH being the most inhibited. This inhibition of mycelial growth reached 75 % when ASM was applied at concentrations higher than 50 mu g ml(-1). ASM also induced an elevated protection against the strain SH in the greenhouse when it was applied twice as foliar sprays at 100 mu g ml(-1) before root inoculation. It reduced leaf alteration index by 67 %, vessel browning index and growth alteration by 80 %. The plant defense activator markedly enhanced accumulation of H2O2. Furthermore, ASM primed tomato seedlings for enhanced activity of peroxidase and polyphenol oxidase. These results suggest that ASM protects tomato from V. dahlia directly by inhibiting the growth of pathogen and indirectly by activating plant defenses responses.