Fruiting in the Higher Fungi

Abstract

Publisher Summary Large elaborate fruit bodies of higher fungi called mushrooms (brackets or toadstools), have attracted attention and are the objects of taxonomic and morphological studies. In the fruit bodies, specialized cells are generated that have genetically different haploid nuclei fuse to form diploid nuclei. The diploid cells do not propagate but undergo meiosis to form haploid spores. The vegetative mycelium colonizes the substrate, and its growth depends on regularly branching hyphae. In the heterothallic basidiomycetes, fruiting is observed regularly or exclusively in the heterokaryon, also called the secondary mycelium, that arises from a mating between two compatible homokaryons. It ensures that diploid cells (basidia) that are formed in fruit bodies produce recombinant meiotic progeny (basidiospores). Haploid fruiting may occur spontaneously, only under stress conditions such as transfer to nutritionally deficient media or injury, or only after applying fruit-body formation-inducing substances. The chapter describes molecular and biochemical indices of fruiting. Environmental conditions such as light, temperature and ambient carbon dioxide concentrations, affect the initiation and further development of fruit bodies in basidiomycetes. Formation of large fruit bodies in basidiomycetes and some members of the ascomycetes can be considered as a special case of emergent growth in fungi. The commercially most valuable mushrooms—those mostly appreciated for their taste—are borne on mycelia that live in mutual symbiosis with the roots of trees.