The invention is a composition for agricultural use that comprises a biotic compound derived from microalgae, said compound being capable of causing the induction of resistance in plants. The microalgae may be diatoms and/or cyanobacteria. In particular, they may comprise an algal strain selected from the group comprising Phaeodactylum tricornutum, Arthrospira platensis (Spirulina), Euglena gracilis and Porphyridium cruentum.
