Gliocladium virens has shown good antagonism against decay fungi in agar medium and in wood blocks. Gliotoxin produced by Gliocladium virens is associated with biocontrol of some plant diseases, but its importance to biocontrol of wood-attacking fungi is unknown. We investigated the ability of gliotoxin-producing (GLT+) isolates of Gliocladium virens and gliotoxin-deficient (GLT-) mutants of Gliocladium virens to inhibit growth of wood-attacking fungi in agar medium and to prevent decay in wood. The brown-rot fungi, Postia placenta and Neolentinus lepideus and the white-rot fungi, Trametes versicolor and Phlebia brevispora were completely inhibited by the GLT+ isolate and the GLT- mutants in agar medium. The GLT+ isolate also completely inhibited the growth of the brown-rot fungus, Gloeophyllum trabeum and the white-rot fungus, Irpex lacteus but the GLT- mutants caused lesser inhibition. The GLT+ isolate and GLT- mutants were ineffective in preventing growth of mold and stain fungi in dual agar culture. Pretreatment of wood blocks with a GLT+ isolate or GLT- mutant prevented decay by Postia placenta. Likewise, the GLT+ isolate prevented decay by Irpex lacteus but the GLT- mutants did not. Gliocladium virens (GL-21) was grown on a sulfur containing medium at pH 3.5 to enhance antibiotic production. However, inhibition of growth of decay fungi on agar medium containing culture filtrates was not enhanced. Decay was reduced in blocks treated with the culture filtrates but was not completely stopped. The filtrates were also ineffective in preventing growth of mold and stain fungi on wood.

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