Basidiomycetes

The life cycle of a typical basidiomycete is schematically represented in The haploid basidiospore or conidium (A) germinates to the n-mycelium (B, monokaryon, primary mycelium).

There are also asexual anamorphs in Basidiomycetes. According to Muller and Loeffler (1992), asexual anamorphs are supposed to occur almost just as frequently as in Ascomycetes: "they are named however only rarely with an own name, therefore hardly considered in the system of the Deuteromycetes and would be more frequent in the dikaryotic phase". A known example among the wood-decay Basidiomycetes is Heteroba-sidion annosum with its anamorph Spiniger rneineckellus.

In the laboratory, monokaryons are capable of indefinite growth if they are regularly subcultured on fresh medium. In nature, characteristically the dikaryon or secondary mycelium develops. Basidiomycetes do not form sexual organs for plasmogamy, but monokaryotic hyphae come into contact one with another and fuse by somatogamy (C).

If the nuclei are compatible, the dikaryon develops (I)). This long-lived mycelium (Schwantes 1996) represents the essential asidiomycete that penetrates the substratum and absorbs nourishment, in the case of wood fungi with wood-decay function (D-G). In about half of the Basidiomycetes, the dikaryon grows by clamp connections (clamp mycelium)

Generalized life cycle of a homobasidiomycete. A hasitliospores or B monokaryons after germination, C somatogamy, D dikaryon, E-G clamp formation, H-K basidium devepment, I karyogamy, J meiosis, K basidium with lour basidiospores located in sterigmata

A short branch arises on the side of the apical hypha and bends over. After synchronous ("conjugate") division of the two nuclei (E), two daughter nuclei remain in the apical cell, one nucleus migrates into the branch (F), the branch end fuses with the subapical cell, and by septum formation, two dikaryotic hyphae have developed (G). Repeated conjugate divisions accompanied by septum formation result in an extensive dikaryotic mycelium (Jennings and Lysek 1999).

Sometimes there are double or multiple (whorl) clamps (maxi-mally eight) around one septum, e.g., in Coniophora puteana (four clamps). In a second method of dikaryotization, there is a division of the nuclei in the bi-nucleate hypha followed by a migration of the daughter nuclei into the primary mycelium of the opposite mating type. The foreign nucleus in each mycelium divides and its progeny migrate from hypha to hypha through the septal pores until both parent mycelia have been dikaryotized (Alexopolus and Mims 1979). Depending on external factors, like season (temperature, air humidity), nu-trients and light, large fruit bodies (tertiary mycelium, basidiocarp, basidioma) develop on the secondary mycelium . In the fruit body of the hymenomycetes, the hymenium (fertile layer) develops in which the formation of basidia occurs .

Life cycle of a wood-decay basidiomycete. A haploid spores, hyphae, somatogamy and dikaryotic growth in the soil, B infection of the tree through a wound, C tree deterio-ration by the dikaryon, D fruit body formation (bracket); in the hymenium: E karyogamy, F, G meiosis, H mature basidium with four basidiospores

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Ecosia ; Ecology Search

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