Jean-Marc Olivier

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

Trichoderma harzianum biotype Th2, re- sponsible 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 per- formed in conventional compost to further our un- derstanding of how Trichoderma Th2 establishes and competes with the button mushroom. Spore germi- nation of Th2 isolates was little affected by A. bisporus mycelium while that of other species was strongly in- hibited. Th2 mycelium flourished in compost unin- oculated or inoculated with A. bisporus, but myceli- um 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. bis- porus was dramatically reduced and typical green

Selfreproduction induced variability in agronomic traits for a wild Agaricus bisporus

Consequences of selfreproduction (in- tramictic reproduction) were studied on a wild Agar- icus bisporus var. bisporus strain. Individual variations were observed on several agronomic traits, natural cap color, susceptibility to bacterial blotch, mycelial growth and yield, for each of the two studied intra- mictic generations. RAPD markers showed a high lev- el of recombination between intramictic generations. With all traits, the same level of transgression was ob- tained at each generation, with the exception of my- celial growth which dramatically increased in the first generation. Bacterial blotch susceptibility decreased, reaching a threshold, therefore resistance was not reached. Variability induced by intramictic reproduc- tion in A. bisporus could be integrated favorably in breeding programs.

Receptivity of cloned hazels to artificial ectomycorrhizal infection by Tuber melanosporum and symbiotic competitors

Abstract The cultivation of the black truffle, Tuber melanosporum (Vitt.), is based upon plantation of seedlings artificially infected with Tuber. At the present time, neither the host-plant nor the fungal material used for planting truffle orchards are genetically well defined. Cloning the host-plant was performed as a first step in improvement. A clone of hazel (Corylus avellana L.) was artificially infected with T. melanosporum. The heterogeneity of the root volume was not completely suppressed by cloning but very extensive growth unfavorable to Tuber colonization rarely occurred. The root system was highly receptive to ectomycorrhizal fungi. The percentage of roots infected by T. melanosporum reached a higher level on cloned hazels than uncloned seedlings. The relation between Tuber and other symbionts appeared to depend on the morphology of the root system. T. melanosporum spread more easily on medium-sized root systems whereas the other symbionts (Scleroderma sp., Cenococcum sp., Pulvinula globifera) developed in parallel to the root volume. The practical potential of this system is discussed.

Compétitions entre symbiotes sur jeunes noisetiers truffiers

Summary One-year-old hazel seedlings, infected with Tuber melanosporum, were transfered from a nursery substrate to pots filled with disinfected truffle-orchard soil in order to observe the development of T. melanosporum and other symbionts. The overall infection and the colonization by each type of symbionts were related to the development of the roots. Hazel seedlings with very extensive root systems were more affected by competitive symbionts than less developed plants. Colonization by some symbionts induced the exclusion of T. melanosporum.