Ceratobasidium


Ceratobasidium is a genus of fungi in the order Cantharellales. Basidiocarps are effused and the genus is sometimes grouped among the corticioid fungi, though species also retain features of the heterobasidiomycetes. Rhizoctonia-like anamorphs of Ceratobasidium species are placed in the genus Ceratorhiza. Species are saprotrophic, but several are also facultative plant pathogens, causing a number of commercially important crop diseases. Some are also endomycorrhizal associates of orchids.

Taxonomy

Ceratobasidium was introduced in 1935 by American mycologist D.P. Rogers to accommodate species of the old form genus Corticium that showed affinities with the heterobasidiomycetes. These affinities were the possession of large sterigmata and the production of basidiospores that produce secondary spores. Four species were originally placed in the genus, with subsequent authors adding a further 35 species.

Current status

Research on the septal pore ultrastructure of the little-known and atypical type species, Ceratobasidium calosporum, indicates that it is a member of the Auriculariales and is unrelated to other species of Ceratobasidium. This taxonomic problem has not yet been resolved. Molecular research, based on cladistic analysis of DNA sequences, places Ceratobasidium within the Cantharellales.

The genus ''Ceratorhiza''

Many Ceratobasidium species produce anamorphic hyphal states, sometimes with sclerotia, that were originally placed in the form genus Rhizoctonia. With a move to a more natural classification of the fungi, the new genus Ceratorhiza was introduced for anamorphs of Ceratobasidium by R.T. Moore in 1987. Some ten species have been described in Ceratorhiza, several of which are not linked to any known teleomorph.

Description

Fruit bodies are effused, thin and often inconspicuous, smooth, waxy to dry and web-like, whitish to pale grey. Microscopically they have comparatively wide hyphae without clamp connections and basidia that are spherical to cuboid or broadly club-shaped. Basidia bear 2 to 4 sterigmata, which are comparatively large. Basidiospores are globose to cylindrical, smooth, and colourless. They frequently produce secondary spores and germinate by hyphal tubes. Ceratorhiza anamorphs produce hyphae and occasionally sclerotia.

Habitat and distribution

Species are mainly saprotrophic, occurring in the soil and producing fruit bodies on dead stems and plant detritus. Some occur on attached leaves and stems. Several species have been isolated from orchid mycorrhiza. Distribution appears to be cosmopolitan.

Economic importance

Ceratobasidium species are opportunistic parasites of plants, causing a variety of economically important diseases. Examples include: Ceratobasidium cereale, the cause of sharp eyespot of cereals; Ceratobasidium oryzae-sativae, the cause of aggregate sheath spot of rice; and Ceratobasidium noxium, the cause of kole roga or black rot of coffee.