Ceratorhiza R.T. Moore (anamorph)
Ceratobasidium is a genus of fungi in the order Cantharellales. Basidiocarps (fruit bodies) 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.
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 ("Cerato-basidium" means "horned basidium") 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.
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 (excluding the type species) 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.
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 (elongated and worm-like in the type species), smooth, and colourless. They frequently produce secondary spores and germinate by hyphal tubes. Ceratorhiza anamorphs produce hyphae (sometimes swollen) and occasionally sclerotia (small propagules composed of thick-walled hyphae).
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.
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.
- Rogers DP. (1935). "Notes on the lower Basidiomycetes". University of Iowa Studies in Natural History 17: 3–43.
- Weiss M, Oberwinkler F. (2001). "Phylogenetic relationships in Auriculariales and related groups – hypotheses derived from nuclear ribosomal DNA sequences". Mycological Research 105 (4): 403–415. doi:10.1017/S095375620100363X.
- Moncalvo J-M et al. (2006). "The cantharelloid clade: dealing with incongruent gene trees and phylogenetic reconstruction methods". Mycologia 98 (6): 937–948. doi:10.3852/mycologia.98.6.937. PMID 17486970. http://www.endophytes.org/teaching/advmycol/Cantherelloid.Moncalvo.pdf
- Moore RT. (1987). "The genera of Rhizoctonia-like fungi". Mycotaxon 29: 91–99.
- Roberts P. (1999). Rhizoctonia-forming fungi. Kew: Royal Botanic Gardens. p. 239. ISBN 1-900347-69-5.
- Murray DIL, Burpee LL. (1984). "Ceratobasidium cereale sp.nov., the teleomorph of Rhizoctonia cerealis". Transactions of the British Mycological Society 82: 170–172. doi:10.1016/S0007-1536(84)80227-2.
- Lanoiselet VM, Cother EJ, Ash GJ. (2007). "'Aggregate sheath spot and sheath spot of rice". Crop Protection 26 (6): 799–808. doi:10.1016/j.cropro.2006.06.016.