PRODUCTION OF ANTIFUNGAL METABOLITES BY THE ECTOMYCORRHIZAL FUNGUS PISOLITHUS-TINCTORIUS STRAIN SMF

An ectomycorrhizal fungus, Pisolithus tinctorius strain SMF, isolated from a basidiocarp removed from the roots of a recently fallen old growth fir in the Smoky Mountains of Tennessee, was characterized for its in vitro production of antifungal metabolites. On solid medium P. tinctorius SMF strongly inhibited growth of strains of Fusarium solani, Geotrichum candidum, Phanerochaete chrysosporium, and Verticillium dahliae, all species known to be plant pathogens. Evidence from paired colony growth inhibition studies on agar plates indicated that production of antifungal agents by P. tinctorius SMF may be enhanced by close physical contact with other fungi. The antifungal activity of P. tinctorius SMF was much greater than that of several culture collection strains of P. tinctorius. The culture collection strains either showed no or very limited activity. The antifungal activity was associated with an apparently inducible metabolism of P. tinctorius SMF and with the production of darkly colored water soluble phenolic metabolites. Small scale fermentation studies showed that the phenolics are readily producible by submerged culture fermentation. This is the first report of submerged culture production of antifungal metabolites by an ectomycorrhizal fungus.