Interactions between the Pathogen Trichoderma harzianum Th2 and Agaricus bisporus in Mushroom Compost

Trichoderma harzianum biotype Th2, responsible for green mold disease, appeared in the North of France by the end of 1997. Cocultures of Agaricus bisporus with four French Th2 isolates and three less aggressive Trichoderma species were performed in conventional compost to further our understanding of how Trichoderma Th2 establishes and competes with the button mushroom. Spore germination of Th2 isolates was little affected by A. bisporus mycelium while that of other species was strongly inhibited. Th2 mycelium flourished in compost uninoculated or inoculated with A. bisporus, but mycelium of the button mushroom is required for intensive sporulation. No fungistatic effect of the mycelium of Trichoderma on A. bisporus was observed in compost, but when Th2 produced spores, toxicity toward A. bisporus was detected. A simultaneous growth of A. bisporus and Th2 was observed before the mycelium of Agaricus stimulated the Th2 sporulation. As soon as sporulation occurred the mycelial growth of A. bisporus was dramatically reduced and typical green mold rapidly developed.