Fruit body initiation and development that occurs usually outside of the sub-strate are affected by various exogenous factors: humidity, temperature, light, nutrition, force of gravity, composition of air, and interactions with other organisms (Schwantes 1996). Endogenous factors cover the participation of phenol oxidases and other enzymes, cyclic adenosine monophosphate (AMP) and genes.
Fruit body formation is often promoted by conditions, e.g., warmth in S. lacrymans, which are unfavorable for the vegetative development. In fungi that are not tolerant to dryness, like Pholiota and Pleurotus species, the fruit bodies frequently have a fleshy consistency and lose when drying their function irreversibly, so that in the northern hemisphere many forest fungi with annual fruit bodies preferentially fructify in damp-cool weather in the autumn. Dry-tolerant fruit bodies, like in Schizophyllum commune, continue spore production under humid conditions after dryness for many years. Others reduce the evaporation by hairy or "varnished" surfaces, like Inonotus and Ganoderma species.
The concentric zonation of the pileus surface (rough and smooth in the change) of Trametes versicolor is influenced by humidity variation and the different colors of the individual zones by light and dark phases (Williams et al. 1981). In Coprinus comatus, fruit body primordia primordia do not develop further without light (Jennings and Lysek 1999). Short-wave light (UV, blue) may influence fruit body development (Schwantes 1996). The Oyster fungus, Pleurotus ostreatus, only fruits below 16 °C , and the less tasty subspecies P. ostreatus ssp.florida at a higher temperature. Fruit bodies of the Winter fungus, Flammulina velutipes, appear also after snowfall. Serpula lacrymans fruits in the laboratory after a stimulating pretreatment of the mycelium for 3 -4 weeks at the submaximal temperature of 25 °C .
Lentinula edodes is stimulated during its cultivation on wood in Asia by a cooling treatment. Schizophyllum commune fruits already on simple nutrient agar at room temperature. Gloeophyllum trabeum (Groan and Highley 1992a) and L. edodes (Leatham 1983) fructified on defined growth media. AMP was suitable for a Coprinus species (Una and Ishikawa 1973).
Yeast extract, vitamin B1, traumatic influences through physical distortions to the mycelium, and the presence of another fungus or its mycelial extract or culture filtrate may be favorable (Stahl and Esser 1976; Leslie and Leonard 1979; Matsuo et al. 1992; Kawchuk et al. 1993). In S. commune, the development of a fruit-body-inducing substance (FIS) is genetically controlled (Leslie and Leonard 1979).
In a Polyporus species, there are fi+ genes (fruiting initiation) (Stahl and Esser 1976; Esser 1989). The force of gravity determines that the yearly hymenial layers in the bracket-like, perennial fruit bodies of Fomes fomentarius also point to the earth center if the host tree is lying on the ground .
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