FUNGI IMPERFECTI or DEUTEROMYCETES

The form-division Fungi imperfecti or Deuteromycota is an artificial category. Members of this group were originally combined into a single group because they apparently lacked a sexual stage. However, it is generally believed that the majority of fungi imperfecti represent the nonsexual stages (anamorphs) of sexually reproducing fungi that belong to the Ascomycetes or Basidiomycetes, with the majority from the former, (Moore-Landecker, 1996). Fungi imperfecti are divided into form-classes based upon morphological similarities. The criteria that are typically used are colour, shape, size and septation of the conidia (whether the spores are unicellular, or made up of multiple cells). The effect of this is that unrelated fungi have been 'lumped' together while possibly related fungi have been classified into different form-classes because of differences in the visual appearance of the spores. For example, many fungi have been placed in the genus Helminthosporium because they form dark, ellipsoid conidia with three or more cells on a dark mycelium. When the sexual teleomorph stage was discovered for some species of Helminthosporium they belonged to two separate genera of Ascomycete: Trichometasphaeria and Cochliobolus. In addition, the teleomorph stage of one species of Curvularia also belongs to the ascomycete genus Cochliobolus. The assumption made by Moore-Landecker (1996) is that the teleomorph stage may be a more reliable index of natural relationships than visual appearance. The difficulty is that for the majority of fungi placed within the Fungi imperfecti form-division only the asexual anamorph stage has been positively identified.

An important fungi imperfecti group is the form-class hyphomycetes.
Hyphomycetes are those fungi imperfecti which form a mycelium but lack a sporocarp. The spores are borne on conidiophores. Hyphomycetes are also called moulds and a culture of hyphomycete can be recognized by the powdery or fluffy appearance of the colony. Examples of hyphomycetes include Penicillium, Epicoccum and Aspergillus.

Many of the spores of the Fungi imperfecti have morphologically distinct features so that the spores from this group are some of the most easily identified. Many are also easily cultured so that more research has been conducted upon this group of fungi than for many other. Alternaria, Cladosporium, Curvularia, Drechslera (including Helminthosporium), Epicoccum, Fusarium, Nigrospora and Stemphylium were listed by Kendrick (1990) as the 'Big Eight' because of their allergenicity and frequency in the air. In addition, Aspergillus and Penicillium are abundant Fungi Imperfecti.

Go forward to Images and Descriptions of some airborne fungi imperfecti spores.

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ASCOMYCOTA

Fungi within the Ascomycota division bear their sexual spores within the ascus. In most cases the asci are borne in or upon a sporocarp, the ascoma. Usually, eight ascosportes are produced in one ascus. There are over 30,000 described species of Ascomycota and the majority are ascomycetes. Ascomycetes include a wide range of diverse organisms such as the yeasts, powdery mildews, cup fungi and the edible morels and truffles. In addition, plant diseases such as blackspot on roses and Dutch elm disease are caused by ascomycetes, (Moore-Landecker, 1996). So although some ascomycetes produce noticable fruiting bodies, the truffles for example, the majority of ascomycetes live and produce spores in structures which are barely visible to the naked eye. Often the whole fungus is contained within the leaf of a plant. Spores from the Ascomycetes division found in the air are numerous and many are known to produce positive reactions in skin-prick test trials, (Kendrick, 1990). Leptosphaeria is the most abundant ascospore during rainy weather. The role of many ascospores in allergy is, as yet, unclear.

Go forward to Images and Descriptions of some airborne ascospores.

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BASIDIOMYCOTA

Basidiomycota is the most morphologically complex fungal division, numbering approximately 25,000 species, (Davis et al., 1988). The spores of this Basidiomycota division are borne on basidia and can be divided into three classes, the Urediniomycetes (Rusts), Ustomycetes (Smuts) and Basidiomycetes (jelly fungi, rusts, smuts, bracket fungi, mushrooms and puffballs). As with spores from the Ascomycota division, far less is known regarding the role of Basidiomycota spores in allergy than for Fungi imperfecti, although research has demonstrated that many are potential allergens, (Burge, 1986, Butcher et al., 1987, Davis et al., 1988, Hasnain et al., 1985, Lehrer et al., 1986, Santilli et al., 1985). Common basidiospores include Ganoderma, Agrocybe, Coprinus and Agaricus (the common mushroom), and those from crop pathogens such as the Rusts and Smuts.

Go forward to Images and Descriptions of some airborne basidiospores.

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SITE INDEX

Home
Introduction
Fungi Imperfecti/Deuteromycota
Ascomycota
Basidiomycota
Fungal Spores and Allergy
Assessing the Effects
Sampling Spores
Culturing
Visual Identification
Details and Images of some common spore types

References
Links