Plant extracts comprising at least a phenolic compound, for inducing the natural defense of a plant against a pathogen, such as Phytophthora infestans

A sugar beet extract (SBE) induced defense in potato plants under green-house conditions and in field trial, without apparent toxicity for the plant. Treatment with SBE resulted in significant reduction of the size of Phytophthora infestans infection lesions and lower sporangia production. SBE had no apparent toxic effect, neither on the hyphal growth of the pathogennor on the germination of sporangia. SBE triggered PR-1 protein induction which suggests that the defense mechanism conferred by SBE could be via direct induced resistance. An array of phenolic metabolites and minerals was found in the SBE and constitutes potential inducers of the defense.