Twenty-two species of thermophilic fungi were isolated from mushroom compost. Scytalidium thermophilum was present in the compost ingredients, fresh straw, horse droppings, and drainage from compost and dominated the fungal biota of compost after preparation. Of 34 species of thermophilic fungi tested, 9 promoted mycelial growth of Agaricus bisporus on sterilized compost: Chaetomium thermophilum, an unidentified Chaetomium sp., Malbranchea sulfurea, Myriococcum thermophilum, S. thermophilum, Stilbella thermophila, Thielavia terrestris, and two unidentified basidiomycetes. These species will be considered for future experiments on inoculation and more controlled preparation of compost.

Agaricus bisporus mushrooms are cultivated on straw compost prepared in the sequence phase I and phase 11. Phase I is a process at 70-80°C for several days up to 2 weeks. Phase I1 is a controlled process at 45°C for 6 days. In phase I1 the thermophilic fungus Scytalidium thermophilum becomes abundant. Its density in finished compost is correlated with the yield of mushrooms. It stimulates the growth rate of mushroom mycelium. Scytalidium thermophilum was inoculated in batches of 1 tonne of pasteurized compost for experimental phase 11. Mushroom yields on these composts were twice those of controls (pasteurized, not inoculated). This indicated that S. thermophilum is important for the conversion of straw to compost. The essential actions for mushroom crop productivity of high temperatures during phase I and of S. thermophilum during phase I1 are unclear.RCsumC : Le champignon Agaricus bisporus est cultivC sur un compost de paille prepart en deux phases ~Cquentielles, phase I et phase 11. La phase I est conduite de 70 i 80°C pendant plusieurs jours, jusqu'i 2 semaines. La phase I1 est un processus contr816, effectuC i 45°C pendant 6 jours. Au cours de la phase I1 le champignon thermophile Scytalidium themophilum devient abondant. Sa densit6 dans le compost fini, est corrtlee avec le rendement en champignons. I1 stimule le taux de croissance du mycClium du champignon. Sur une base experimentale, les auteurs ont inoculC le S. thermophilum dans des brassCes d'une tonne de compost pasteurisC, en phase 11. Les rendements sur ces composts ont Ct C le double de ceux obtenus avec les brassees tCmoins (pasteurisCes et non-inoculCes). Ceci indique que le S. thermophilum est important pour la conversion de la paille en compost. Les r8les essentiels, pour la productivitC en champignons, de la haute tempirature en phase I et du S. themophilum en phase 11, ne sont pas Cvidents.

Scytalidium thermophilum isolates in culture, as well as the endogenous strain(s) in mushroom compost, were inactivated at 70°C. This temperature was used to pasteurize composts for experiments. Of nine thermophilic fungal species, only S. thermophilum and Myriococcum thermophilum grew well on pasteurized compost in test tubes. The effect of both species on the crop yield of Agaricus bisporus mushrooms was studied. In solid-state fermentation rooms called tunnels, compost was pasteurized and inoculated. After incubation, the inoculated organisms were reisolated and counted, showing their successful colonization. The yield of mushrooms on inoculated composts was almost twice that on the pasteurized control. This result demonstrates the effectiveness of S. thermophilum in compost preparation. Inoculation is not necessary for traditional compost preparation. Naturally occurring strains of S. thermophilum, present in ingredients, readily colonize compost during preparation. Inoculation may be vital if compost is pretreated at a high temperature in tunnels. This finding is of relevance for the environmentally controlled production of high-yielding compost.