ABSTRACT
Among the basidiomycetes, the mushroom-forming fungi are of commercial value and thus the production of fruiting bodies has been studied in detail. Mushroom growers are interested in the basic mechanisms underlying fruit body formation in order to improve the yield and to find stable conditions under which high crop yields can be obtained on a regular basis. The induction of fruit body development under defined and sterile conditions, which is prerequisite to study the molecular clues for mushroom formation, is dependent on the growth conditions and therefore easiest with saprophytic fungi. A wide range of basidiomycetes, however, are able to fructificate only in association with a host plant because they live in close association with the plant either in a mutualistic symbiosis or as phytopathogens. These fungi include many edible fungi like the ectomycorrhizal boletes, the wood-rotting, parasitic honey agaric Armillaria, and other valuable edible species. The fungi living in close contact to a host plant, e.g., ectomycorrhizal species [this volume, Chapter 12 by Duplessis et al.], are not able to form fruit bodies without the signals from their host tree. Only in very rare instances have we been able to identify such host signals.
