Acibenzolar-S-methyl induces the accumulation of defense-related enzymes in apple and protects from fire blight.
Acibenzolar-S-methyl is a chemical inducer of systemic acquired resistance in several annual plants. The ability of this novel chemical to induce resistance was studied in a perennial plant (apple) affected by fire blight caused by Erwinia amylovora. Acibenzolar-S-methyl (100 and 200 mg/l active ingredient) protected Golden Delicious seedlings, scions and trees from artificial infection when applied before inoculation. The protection of apple seedlings was similar to the protection obtained with the standard for fire blight control, plantomycin (100 mg/l streptomycin sulfate), applied immediately before inoculation. The mean levels of control in scions in the greenhouse and in trees in orchards in France, were approximately 69% and 50%, respectively. The protection of apple seedlings was constantly associated with the activation of two families of defence-related enzymes, peroxidases and β-1,3-glucanases. Accumulation of both enzymes was induced locally in treated leaves and systematically, especially for β-1,3-glucanases, in upper untreated leaves, and was sustained for at least 17 days. These results suggest that acibenzolar-S-methyl promotes induced systemic resistance in apple by increasing defence-related compounds. This chemical could provide a new approach of control of fire blight but its practical use needs further investigation.