Reproduction of Deuteromycetes

Fungi that reproduce asexually (anamorphic fungi) are either yeasts or Deu-teromycetes. The term "yeast" is descriptive and stands for any fungus that reproduces by budding.

Deuteromycetes (Fungi imperfecti, colloquially: molds) is an artificial as-semblage of fungi that reproduce asexually by conidia (conidiospores), either as the only form for propagation (imperfect fungi) or additionally (anamorph) to a sexual reproduction (teleomorph). When both the anamorph and the teleo-morph are known, the fungus is called a holomorph (the whole fungus).

The teleomorph may have one (mono-anamorphic) or many (pleo-anamorphic) asexual stages. In other words: Deuteromycetes are the conidia-producing forms of a fungus and may or may not be associated with a teleomorph. Many Deuteromycetes are supposed to have a teleomorph in the Ascomycetes, but they may also have basidiomycetous affinity. Also in the wood-inhabiting Deuteromycetes, the teleomorph often is of ascomycetous affinity as in the blue stain and soft-rot fungi, but some are anamorphs of Basidiomycetes like in the Root-rot fungus, Heterobasidion annosum [anamorph: Spiniger meineckellus (A.J. Olson) Stalp.; e.g., Holdenrieder 19891. In the absence of a teleomorph, taxonomic affinity can be detected by the ultrastructure of the cell wall: Ascomycetes have two-layered walls, while the walls of Basid-iomycetes are multilamellar. In terms of strict nomenclature, the teleomorph name takes precedence over the anamorph but in practice, a species is of-ten identified according to the form in which it was found (Eaton and Hale 1993), like in the case of the wood-inhabiting molds Aspergillus and Penicillium.

The Deuteromycetes are usually divided in Coelomycetes and Hyphomy-cetes. Coelomycetes develop conidiophores within fruit bodies (conidiomata). In Hyphomycetes (or Moniliales), conidia develop on simple or aggregated hyphae. Conidium formation and conidiophore morphology are criteria to classify Deuteromycetes . A simplified differentiation for wood-inhabiting Deuteromycetes distinguishes between conidiospore (free cell fragmentation at the hyphal tip or a branch) and sporangiospore (development in a sporangium).

Conidia of wood-inhabiting Deuteromycetes can be defined as mitotically developed (mitospores), immovable, mononuclear to more-nuclear, unicellu-lar to more-celled, pigmentless (hyaline) to white, yellow, orange, red, green, brown, blue, or black colored (depending on the species) spores of different development, size, shape and surface (Fig. 1.9; Reif 1997; Kiffer and Morelet 2000). The variety of the spore pigments causes that molded substrates may be colorful.

Fig. 1.8. Generalized view of conidia according to their development. C conidia, S sporan-o,iospores, A arthrospores, Ch chlamvdospores

Fig. 1.9. Conidia. Example of the manifold shapes and structures

Fig. 1.10. Developmental cycle of a deuteromycete. A conidium, B germ hypha, C development of conidiophore, D development of vesicle, E vesicle with conidia

The series of spore germination, hyphal growth, and conidia production rep-resents the asexual reproduction cycle of a deuteromycete fungus, illustrated in Fig. 1.10 by an Aspergillus species.

The biological advantage of the conidia production to the Deuteromycetes (and anamorphs of Asco and Basidiomycetes) is that these fungi can exit from an exploited substrate to arrive fresh nutrients by spores (mitospores) in huge numbers without the need of preceding sexuality. Distributed randomly by and through the air or by adhering to the surface of animals, spores are present everywhere. Disadvantageous is that without (para)sexuality clones of an original hypha are distributed. Conidia can develop independently from the karyotic stage of the hypha that is anamorphs can occur both on haploid and dikaryotic mycelium.

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