Pine root exudate stimulates the synthesis of antifungal compounds by the ectomycorrhizal fungus Paxillus involutus

SUMMARY The ectomycorrhizal fungus Paxillus involutus Fr. was grown in the presence of root exudate of Pinus resinosa Ait, for two weeks. The effect of root exudate on the synthesis of ethanol‐soluble antifungal compounds by P. involutus was determined by a bioassay based on microconidial germination of Fusarium oxysporum Schlecht emend, Sny. & Hans f. sp. pini. Cultivation of P. involutus on root exudate led to a greater than two‐fold increase in fungitoxic activity when compared to cultivation on modified Melin Norkrans medium in Petri dishes. Inoculation of P. resinosa root exudate with both P. involutus and a spore suspension of F. oxysporum led to an 80 % suppression of the sporulation of F. oxysporum when compared to controls lacking P. involutus. The increased resistance of P. resinosa P. involutus associations to Fusarium root rot may, therefore, be the result of biosynthesis of antifungal compounds by P. involutus which is stimulated by P. resinosa root exudate.