COLONIES velvety, slightly flocculose, dull olive to dark oliviaceous black, ca. 1.5-2.0 cm diam when 5-day old and ca. 4.0 cm diam when 10-day old and grown on potato dextrose agar (PDA) at a room temperature.
CONIDIOPHORES (cp) macronematous, solitary or, more frequently, in caespitose clusters, robust, erect, straight, rigid to slightly flexuous, becoming markedly geniculate in apical, fertile portion following sympodial growth associated with serial conidiation, smooth, cylindrical, thick-walled, cicatrized, with scars relatively prominent, septate, occasionally branched, sometimes nodose, mid to pale brown, bulbous at the base, up to 300 µm long and 4-8 µm wide, up to 9 µm wide at the intercalary swellings, 6-10(-12) µm wide at the base.
CONIDIA (c) in long, branched chains. Ramoconidia cylindrical to clavate, ampulliform, sometimes slightly curved, ranging from smooth to verrucose, 0-4-septate, cicatrized, mid to pale oliviaceous green, 6-36 x 4-8 µm, mostly 12-20 µm long. Intercalary conidia ellipsoidal to limoniform, oblong to fusiform, pale olive brown, smooth to verruculose, 0-1-septate, up to 25 µm long, 4-8 µm wide. Terminal conidia subglobose to oblong, 4-8 µm.
SUBSTRATE AND DISTRIBUTION. Cladosporium herbarum commonly occurs on herbaceous and woody plants (McKemy and Morgan-Jones 1991). It is a stable component of populations of microorganisms of living all above-ground plant parts and seeds of different plant species (Blaszkowski 1994a-c, 1995; Brooks 1953; Domsch et al. 1980). Additionally, it has been isolated from soil and man-made substrates.
Cladosporium herbarum is a cosmopolitan fungus, especially in temperate climates (Brooks 1953; McKemy and Morgan-Jones 1991).
NOTES. Morphological and molecular investigations of different Cladosporium-like hyphomycetes have revealed Cladosporium s. lat. to be heterogeneous (Braun et al. 2003). Morphologically, the genus Cladosporium s. str. is distinguished from other Mycosphaerella anamorphs by its unique scars and conidial hila. According to David (1997), fungi of the genus Cladosporium have coronate conidiogenous scars and conidial hila of the "Cladosporium-type", e. g., protuberant with a central dome surrounded by a raised rim. In contrast, ascomata of the teleomorphs of Cladosporium spp. are morphologically identical to those of Mycosphaerella (sect. Tassiana).
Molecular investigations of different species of the genus Cladosporium s. str. showed them to represent a sister clade to Mycosphaerella s. str. and consequently a new teleomorph genus, Davidiella, has been erected (Braun et al. 2003).
The teleomorph of C. herbarum is Davidiella tassiana (De Not.) Crous & U. Braun (Braun et al. 2003).
Cladosporium herbarum frequently occurs on cereals and grasses, where it is associated with so-called "glume or black head mold" and "leaf mold" symptoms (Blaszkowski 1994a-c, 1995). Heavily colonized leaves and other plant parts are appreciably discoloured.
The pathogenicity of C. herbarum is not fully elucidated (Smith et al. 1988). Results of various studies suggest that the ability of C. herbarum to parasitize the plant hosts examined is generally limited. Under favourable conditions, isolates of this fungus were able to penetrate green, healthy leaves, but were mainly confined to sub-stromatal cavities and only a few host cells were killed.
The species most closely related with C. herbarum is C. macrocarpum Preuss, a fungus frequently co-occurring with the former one. Cladosporium macrocarpum differs from C. herbarum by possession of larger, more regularly verrucose conidia, shorter conidial chains, more pronounced prolongations of the conidiophores, and a tendency to produce crustose stromata on agar.
However, Barr (1958) found the anamorph of M. tassiana to be quite variable and that different isolates may be considered either C. herbarum or C. macrocarpum.
Barr M. E. 1958. Life history studies of Mycosphaerella tassiana and M. typhae. Mycologia 50, 501-513.
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Domsch K. H., Gams W., Anderson T. 1980. Compendium of soil fungi. Acad. Press. London-New York-Toronto-Sydney-San Francisco.
McKemy J. M., Morgan-Jones G. 1991. Studies in the genus Cladosporium sensu lato. V. Concerning the type species, Cladosporium herbarum. Mycotaxon 42, 425-440.
Smith I. M., Dunez J., Lelliott R. A., Phillips D. H., Archer S. A. 1988. European handbook of plant diseases. Blackwell Scientific Publications.