"Laboratoires Goemar" have identified, isolated and industrially extracted from a brown alga a natural mol., a β-1-3-glucan (GL32) which stimulates plant defense reactions and induces resistance to diseases.GL32 consists of several units of D-glucopyranosides linked by 1-3 bonds and branches linked by 1-6 bonds.GL32 is harmless to humans and the environment.Treatment of tobacco, tomato and wheat cell cultures as well as wheat seedlings with GL32 induced metabolic changes typical of defense responses: early events (such as ionic fluxes, phosphorylations, oxidative burst), stimulation of the phenylpropanoid and lipid-derived pathways (leading to the signals salicylic acid and jasmonates, resp.), and production of PR-proteins (known for their high antimicrobial potential).While GL32 had no direct antifungal activity, spraying with GL32 at low concentrations (20 to 50 g ha-1) protected wheat seedlings against infection by Septoria tritici and Erysiphe graminis.When combined with synthetic fungicides, GL32 increased their efficacy at low concentrationsThe origin of GL32, its protection potential against important diseases and its mode of action (stimulation of the plant's natural defense responses) open a new path to plant protection for farming procedures that respect the environment.