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