Interactions between the pathogen Trichoderma harzianum Th2 and Agaricus bisporus in mushroom compost

Trichoderma harzianum biotype Th2, responsible for green mold disease, appe ared in the North of France by the end of 1997. Cocultures of Agaricus bisp orus with four French Th2 isolates and three less aggressive Trichoderma sp ecies were performed in conventional compost to further our understanding o f how Trichoderma Th2 establishes and competes with the button mushroom. Sp ore germination of Th2 isolates was little affected by A. bisporus mycelium while that of other species was strongly inhibited. Th2 mycelium flourishe d in compost uninoculated or inoculated with A. bisporus, but mycelium of t he button mushroom is required for intensive sporulation. No fungistatic ef fect 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 occurre d the mycelial growth of A. bisporus was dramatically reduced and typical g reen mold rapidly developed.