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Hypomyces species, especially H. rosellus (Alb. & Schw.) Tul. (anamorph Cladobotryum dendroides (Bull.) W. Gams & Hoozemans) cause the economically significant cobweb disease of cultivated mushrooms, attacking Pleurotus as well as Agaricus culture (van de Geijn, 1982; Gray & Morgan-Jones, 1981). A useful review of the older literature is given by Arnold (1976), and modern taxonomic treatments are given by Gams & Hoozemans (1970) and de Hoog (1978).
Vegetative growth white or pale, with hyaline trailing hyphae or forming simple loose masses on the host, with whorls or dense clusters of conidiogenous cells forming balls of dry and powdery conidia.
Conidia produced singly and separately, from short globose or flask-shaped conidiogenous cells which have an apical denticulate rhachis with a distinctly zig-zag appearance. Conidia one-celled, hyaline, thin-walled, smooth, globose to ellipsoidal, sometimes with an apiculate base.
Beauveria species are ubiquitous and well-known as insect pathogens, but have been recorded from other sources, mostly of animal origin. They can also be isolated from the soil in which their hosts overwinter. No teleomorphs are known.
There is much early literature on the genus, but more recently it has been discussed by de Hoog (1972) and Samson & Evans (1982). The most up-to-date taxonomic treatment is by Mugnai et al. (1989), who recognized seven species, almost all from diseased arthropods. Brady (1979) has provided descriptions of two of the most important species. Their industrial interest lies in the field of biological control.
Beauveria bassiana (Bals.) Vuill. is the best-known species. It has closely clustered conidiogenous cells and globose to broadly ellipsoidal, occasionally apiculate conidia 2-3 x 2-2.5µm in size. B. bassiana was first recorded as the “white muscardine” disease of silk worms.
Beauveria brongniartii (Sacc.) Fetch is less common, is also referred to as “white muscardine” and is also used in biological control. It often has slightly less closely clustered conidiogenous cells, and conidia (2-) 2.5-4 (-6)µm in length which are always cylindrical or ellipsoidal rather than globose.
Stromata superficial, fleshy, usually brightly coloured, discoid or pulvinate (cushion-shaped). Ascomata globose to pyriform. Asci cylindrical, narrow, thin-walled, with a conspicuously thickened apex penetrated by a narrow canal; not blueing in iodine. Ascospores filiform, multiseptate, fragmenting into part-spores.
Conidiomata usually multilocular, the locules tubular, flask-shaped, ovoid or globose, without clearly-defined walls, releasing conidia though irregular splits. Conidiophores branched irregularly. Conidiogenous cells mostly arising as irregular lateral branches, ± cylindrical, producing conidia successively though, a single apical conidiogenous locus. Conidia usually ellipsoidal to fusiform, hyaline, aseptate.
Considering the interest in these fungi as agents of biological control, it is surprising that there has been no comprehensive monograph of Hypocrella and Aschersonia for seventy years (Fetch, 1921). Useful work on classification of the fungi has been contributed by Mains (1960). The book by Samson et al. (1988) is a useful modern source reference for this and other entomogenous fungi.
The best-known species is the common Aschersonia aleyrodis Webber, which is not known to have a teleomorph. It exerts a natural control over scale insects in the tropics, and is used as a biological control agent of the citrus whitefly Dialeurodes citri and the common greenhouse whitefly Trialeurodes vaporariorum. A. aleyrodis is described more fully by Brady (1984) and Sutton (1980).
Resting structures (sclerotia) large, elongated, dark brown, usually leathery, developing from host inflorescences.
Anamorph developing on the surface of the resting structures, accompanied by sugary secretions (honeydew). Conidiophores poorly-developed, hardly distinguished from vegetative mycelium, hyaline, branched. Conidiogenous cells in small clusters, flask-shaped, producing conidia successively from single apical conidiogenous loci.
Ascostromata produced from resting-structures after overwintering, long-stalked, brightly coloured, with a ± spherical head. Ascomata perithecial, usually ovoid, thin-walled, brightly coloured. Asci cylindrical, conspicuously elongated, with a glassy apical cap penetrated by a narrow pore. Ascospores usually helically coiled, filiform, multiseptate, ± hyaline, usually breaking apart into part-spores.
Claviceps species have been well-known since early times as ergot fungi, the fungus infecting cereals and causing serious illness and death for those eating infected grain. More recently, there has been intense research into the use of metabolites produced by Claviceps species in the pharmaceutical industry. See Mantle (1975) for a review of this subject. Similar useful metabolites are produced by endophytic relatives of Claviceps, by Epichloe and by fungi referred for convenience to the form-genus Acremonium. The relations between these fungi and their hosts, and the evolutionary implications of toxin production, are discussed by Clay (1988).
Ascomata usually globose, consisting of spore “cysts”, with smooth apparently acellular walls. Paraphyses absent. Asci deliquescent at a very early stage, very difficult to observe. Ascospores spherical, sticky, aseptate, smooth-walled, not dispersed in clusters. Anamorph Chrysosporium-like.
Bettsia is best-known as an inhabitant of beehives. Unlike the other member of this order Ascosphaera Olive & Spiltoir, which is parasitic on the larvae and which has aggregated ascospores which are dispersed in “spore balls”, Bettsia is a saprobe, and the only species B. alvei is also found as a spoiler of foodstuffs with a high osmotic potential. See Skou (1972, 1975) for further information.
Colonies rapidly growing, white or becoming pale greenish or pale brown. Ascomata 15-42 µm diam, very variable in shape, but most usually ± spherical. Ascospores 3-5 µm diam, spherical. Conidia formed singly at the ends, on short protrusions, or intercalary, sometimes in short chains, separating by the breaking down of the intervening cell walls, 6-11.5 x 4.5-9 µm, ± hyaline, rather thick-walled, smooth, aseptate, the terminal conidia globose to clavate and the intercalary conidia usually barrel-shaped.
Apart from the importance of this fungus to apiarists, it is sometimes isolated from foods with high sugar contents, such as dried fruit (Pitt & Hocking, 1985a). These authors separate Chysosporium fastidium Pitt from the anamorph of Bettsia alvei on the basis of growth rates, colony pigmentation and conidial size, but van Oorschot (1980) did not distinguish between them.
Other anamorphic fungi which may be related to Bettsia alvei include Chrysosporium inops Carmichael and C. xerophilum Pitt, which lack lateral conidia and does not grow so rapidly on sugar-rich media. C. inops has been isolated from dried fruit, powdered spices and a starch mould for a gelatin-containing confection, and C. xerophilum from prunes and stored maize (Pitt & Hocking, 1985a).
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