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You are here: Home / Archives for clavicipitales

Clavicipitales: Verticillium Nees

Jackson Kung'u

Colonies moderately rapidly growing. Conidiophores fairly well differentiated from the usually hyaline vegetative hyphae, erect or prostrate, hyaline or pigmented, verticillately branched over most of their length, with successive whorls of conidiogenous cells. Conidiogenous cells slender, gradually tapering, producing conidia successively from single apical conidiogenous loci. Conidia small, hyaline, usually aseptate, in most species aggregating into spherical slimy heads but formed in chains in a few taxa.

Verticillium is clearly an unnatural form-genus, with links both to the Clavicipitales and to the Hypocreales. Many of the species of interest to the industrial mycologist have links with the Clavicipitales, so the form-genus is treated here. However, the type species V. tenerum Nees has links with the Hypocreales, and a few other species of Nectria have since been reported with Verticillium anamorphs, but the anamorph has such a simple structure that it is likely that convergent evolution has taken place.

The latest taxonomic work on Verticillium is the study by Jun et al. (1991), which compared isolates of V. lecanii from insect and fungal hosts. Further information may be found in Domsch et al. (1980), Ellis (1971), Evans & Samson (1986), Gams (1971, 1988) , and Gams & van Zaayen (1982). Verticillium species are widespread in soil, and are pathogens of other fungi, insects and plants. Recently, they have become important in biological control programmes.

Verticillium albo-atrum Reinke & Berthold

Colonies white at first, then turning black in patches. Conidiophores usually only with one order of branching, hyaline though sometimes with a darkened base. Conidiogenous cells in whorls of 2-4, narrow, gradually tapering. Conidia 3.5-10.5 x 2-5µm, ellipsoidal to cylindrical, hyaline, occasionally septate. This species is a serious parasite, causing wilt diseases of many plants. Verticillium dahliae Kleb. is also a serious pathogen, which has dark multicellular resting structures sometimes referred to as microsclerotia, hyaline conidiophores, and slightly smaller conidia.

Verticillium fungicola (Preuss) Hassebrauk

Colonies white to cream, powdery to velvety. Conidiophores erect, with a single order of branching. Conidiogenous cells in whorls of 3-9, narrow, gradually tapering. Conidia 3-8.5 x 1-2.5µm, ellipsoidal to cylindrical, sometimes curved in older colonies, aseptate. Resting spores not produced.

This species, also referred to in some circles as Verticillium malthousei Ware, causes the diseases of commercial mushroom beds known as “dry bubble” and “brown spot”. It can cause serious losses.

Verticillium psalliotae Treschow is similar to V. fungicola, but has less-branched conidiophores which are usually prostrate, purple pigments at the edge of the colonies, Conidiogenous cells usually in groups of 2-3, and conidia which are crescent-shaped in young cultures and cylindrical to ellipsoidal in older colonies. V. lamellicola (F.E.V. Sm.) W. Gams is similar to V. psalliotae, but has conidia which are not curved. It also causes diseases of mushroom beds.

Verticillium lecanii (Zimmermann) Viegas

Col0nies white to pale yellow, cottony. Conidiophores not well-developed, erect or prostrate, with a single order of branching. Conidiogenous cells in whorls of 3-5, narrow, gradually tapering. Conidia variable in size (dependent on the host), ranging between 2.3-10µm in length and 1-2.6µm in width, cylindrical to ellipsoidal.

Interest in Verticillium lecanii as an agent of biological control is considerable. The fungus is pathogenic on a number of economically important insects, and strains are also parasitic on rust and other fungi. Jun et al. identified a number of taxonomic groups within the species aggregate largely based on host preference. The fungus also produces antiviral agents (Bucknall et al., 1973).

Verticillium tenerum Nees

Colonies growing rapidly, velvety, brick-red to orange-brown. Conidiophores erect, stiff, strongly pigmented, often branched several times. Conidogenous cells 12-23 x 2-4µm, flask-shaped. Conidia 3.5-5 x 2-2.5µm, pale reddish brown in mass. Resting structures not produced. This fungus is better-known under the name Verticillium lateritium (Ehrenb.) Rabenh, and the synonym Acrostalagmus cinnabarinus Corda may also be familiar to some. It has been reported to be the anamorph of Nectria inventa Pethybridge, but that fungus is poorly-known, and is certainly not a typical Nectria. The evidence of connexion is based solely on a single early report (Pethybridge, 1919), and the teleomorph has not recently been found. V. tenerum is a common and cosmopolitan soil fungus. It has also been found on paper, cloth, cotton fibres in conveyor belts, and rotting vegetables, and been isolated from milk, cheese, giner, wheat and salami (Domsch et al., 1980; Pitt & Hocking, 1985a).

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Filed Under: Fungi Tagged With: clavicipitales, Hypocreales, Nectria, Verticillium

Clavicipitales: Paecilomyces Bainier

Jackson Kung'u

 Paecilomyces is a form-genus with connexions to various teleomorph genera, belonging to the Clavicipitales and Eurotiales. Paecilomyces section Paecilomyces (the type subgroup of the form-genus which contains the original described species) has links to the Eurotiales. Paecilomyces section Isarioidea Samson on the other hand, belongs to the Clavicipitales, and the following description refers to this group. Several species in this group are important as agents of biological control. See Samson (1974) and Domsch et al. (1980) for comprehensive descriptions, keys to the genus, and further information.

Colonies often brightly coloured. Hyphae hyaline to slightly pigmented. Conidiophores with several verticillate branches, sometimes aggregated into synnemata. Conidiogenous cells in whorls of 2-7 at the apex of branches and often inserted laterally also, flask-shaped, usually rather less elongated than in Paecilomyces section Paecilomyces, producing conidia successively from apical loci. Conidia formed in chains with the oldest one at the apex, smooth or ornamented, hyaline or brightly coloured, rarely septate. Resting-spores present in some species.

Paecilomyces carneus (Duche & Heim) A.H.S. Brown & G. Smith

Colonies growing slowly, matted, sometimes powdery, at first pure white but becoming pale pink with a green reverse. Conidiophores hardly differentiated, with a few usually verticillate branches. Conidiogenous cells in whorls of 2-4, 9-18 x 1.5-2.5µm, flask-shaped with a distinct neck. Conidia 3-4 x 2-2.5µm, ± globose to ellipsoidal, roughened with tiny spines.

Paecilomyces carneus is found on a wide range of substrates, and especially from soil. It is sometimes isolated from insects, though it appears not to be strongly pathogenic. Several metabolites of the antibiotic group cephalosporins are produced by some isolates (Kitano et al., 1974).

Paecilomyces farinosus (Holm) A.H.S. Brown & G. Smith

Colonies growing quite rapidly, felty or powdery, at first white but often eventually becoming yellowish. Conidiophores verticillately or irregularly branched, sometimes aggregating into synnemata. Conidiogenous cells 5-15 x 1.5-2.5µm, the basal part swollen, tapering towards the apex. Conidia 2-3 x l-2µm, ellipsoidal to fusiform, smooth-walled, hyaline. Resting-spores not produced.

Paecilomyces farinosus is a well-known insect pathogen, and there has been interest in its use as an agent of biological control. The species is polyphagous, but isolates are commonly restricted in their host preferences. P. farinosus is also commonly isolated from soil.
Domsch et al. (1980) state the teleomorph of this fungus to be Cordyceps memorabilis CBS., but the anamorph species as currently recognized is morphologically simple but polymorphic, and in practice the name P. farinosus would probably cover the anamorphs of a range of species of the Clavicipitales (Samson, 1974) . Teleomorphs are not as a rule produced in culture.

Paecilomyces fumosoroseus (Wize) A.H.S. Brown & G. Smith

Colonies growing fairly rapidly, deeply floccose, white at first but becoming dull pink, the reverse pale yellow. Conidiophores erect, sometimes aggregated into pale pink synnemata, with often closely-spaced verticillate branches. Conidiogenous cells in whorls of 4-6, 5.5-8 x 1-2µm, the basal part globose to ellipsoidal and with a distinct neck. Conidia 3-4 x 1-2µm, cylindrical to fusiform, hyaline to pale pink. Resting-spores not produced.

Paecilomyces fumosoroseus is an insect parasite, causing economic damage to silkwork production in eastern Asia (Samson, 1974), and has also been investigated for biological control. It has also been isolated from soil, butter and gelatin.

Paecilomyces lilacinus (Thorn) Samson

Colonies growing rapidly, floccose, at first white but becoming purplish or greyish violet, with a light to dark purple reverse. Conidiophores variably developed, often rather thick-walled, yellowish or purple at the base, sometimes aggregated into synnemata, verticillately branched. Conidiogenous cells in whorls of 2-4, 7.5-9 x 2.5-3µm, flask-shaped. Conidia 2.5-3 x 2-2.5µm, ellipsoidal to fusiform, hyaline but purple in mass. Resting-spores not produced.

Paecilomyces lilacinus has been found on insects on numerous occasions, but is most commonly encountered in isolations from soil. It has also been implicated as a human and animal pathogen, is found on various organic substrates including plastic contact lenses, synthetic rubber and polyurethane, and is used in fungus resistance testing. Strains produce the antibiotics leucostatin and lilacin (Arai et al., 1973). P. lilacinus was originally described as Penicillium lilacinum Thorn, but its colonies lack the characteristic green colour of Penicillium species, its Conidiogenous cells have distinct necks, and its Conidiophores are not divaricately branched (Samson, 1974),.

Paecilomyces marquandii (Massee) S. Hughes is very similar to P. lilacinus, but has colonies with a yellow reverse, smooth-walled hyaline conidiophores, and small globose to ellipsoidal resting-spores are often present.

Paecilomyces tenuipes (Peck) Samson

Colonies rather slow-growing, floccose or powdery, at first white but becoming cream or pinkish buff. Conidiophores erect, hyaline, sometimes aggregated into synnemata, with short branches arranged verticillately or irregularly. Conidiogenous cells in whorls of 2-6, 4.5-6.5 x 2.5-3.5µm, the basal part globose and with a ditinct neck. Conidia 3-7.5 x 2-2.5µm, ± cylindrical, often curved, smooth-walled, hyaline, sometimes septate, the septate conidia significantly longer.

Paecilomyces tenuipes is similar to P. farinosus, especially on the insect host rather than in culture, but its colonies lack yellow pigments, the conidiophore branches and conidiogenous cells are shorter and more swollen, and the conidia are larger and cylindrical. Early reports linked P. tenuipes with the teleomorph Cordyceps polyarthra Moller, but these may not be reliable (Samson, 1974).

Filed Under: Fungi Tagged With: clavicipitales, Eurotiales, Paecilomyces

Clavicipitales: Nomuraea Maubl.

Jackson Kung'u

Colonies slow-growing, hyaline to slightly pigmented. Conidiophores erect, verticillately branched, sometimes aggregated into synnemata. Conidiogenous cells in compact whorls, the basal part often swollen, the apex slightly attenauted. Conidia developing in succession from single apical loci, forming dry chains with the oldest at the apex, ellipsoidal to cylindrical, smooth, hyaline or slightly coloured. No teleomorphs are known, but similarities with other anamorphs of the Clavicipitales suggest that the genus belongs to that order. Only one species is well-known.

Nomuraea rileyi (Farlow) Samson

Colonies slow-growing, dense, dusty green. Conidiophores with compact clusters of branches. Conidiogenous cells 4-6 x 2.5-3.5µm, usually short, cylindrical, occasionally with a swollen base, the neck absent or very short. Conidia in dry divergent chains, 3-4 x 2-2.5µm, ellipsoidal, rarely cylindrical, hyaline but green in mass. Nomuraea rileyi is an insect pathogen, attacking larvae and pupae of Lepidoptera and Coleoptera. There has been interest in the use of this fungus as an agent of biological control, though its slow, growth in culture is disadvantageous. See Samson (1974) and Onions (1979) for further information.

Filed Under: Fungi Tagged With: clavicipitales, Nomuraea

Clavicipitales: Hypocrella

Jackson Kung'u

Hypocrella Sacc.; anamorph Aschersonia Montagne, nom. cons.

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).

Filed Under: Fungi Tagged With: Aschersonia, clavicipitales, Hypocrella

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