Uthatobasidium

''Rhizoctonia'' is a genus of fungi in the order Cantharellales. Species form thin, effused, corticioid basidiocarps (fruit bodies), but are most frequently found in their sterile, anamorphic state. ''Rhizoctonia'' species are saprotrophic, but some are also facultative plant pathogens, causing commercially important crop diseases. Some are also endomycorrhizal associates of orchids. The genus name was formerly used to accommodate many superficially similar, but unrelated fungi.

Taxonomy

History

Anamorphs

''Rhizoctonia'' was introduced in 1815 by French mycologist Augustin Pyramus de Candolle for anamorphic plant pathogenic fungi that produce both hyphae and sclerotia. The name is derived from Ancient Greek, ῥίζα (''rhiza'', "root") + κτόνος (''ktonos'', "murder"), and de Candolle's original species, ''Rhizoctonia crocorum'' ( teleomorph ''Helicobasidium purpureum''), is the causal agent of violet root rot of carrots and other root vegetables. Subsequent authors added over 100 additional names to the genus, most of them plant pathogens bearing only a superficial resemblance to the type species. ''Rhizoctonia'' thus became an artificial form genus of anamorphic fungi comprising a diverse range of unrelated species.

As part of a move towards a more natural classification of fungi, American mycologist Royall T. Moore proposed in 1987 that ''Rhizoctonia'' should be restricted to the type species and its relatives, with unrelated species moved to other genera. Unfortunately, this meant that the best-known but unrelated species, ''Rhizoctonia solani'', would have undergone a name change to ''Moniliopsis solani''. To avoid this, it was subsequently proposed that ''R. solani'' should replace ''R. crocorum'' as the type species of ''Rhizoctonia''. This proposal was passed and the type of ''Rhizoctonia'' is now conserved as ''R. solani'' under the International Code of Nomenclature for algae, fungi, and plants.

R.T. Moore retained species having teleomorphs in the genus ''Thanatephorus'' within ''Rhizoctonia'', but moved those with teleomorphs in the genus ''Ceratobasidium'' to the new anamorphic genus ''Ceratorhiza''.

Teleomorphs

In 1956, Dutch mycologist M.A. Donk published the new teleomorphic genera ''Thanatephorus'' and ''Uthatobasidium'' simultaneously, reserving the former for plant-pathogenic species producing sclerotia-bearing ''Rhizoctonia'' anamorphs (with ''T. cucumeris'' as the type) and the latter for saprotrophic species not producing anamorphs (with ''U. fusisporum'' as the type). In 1996, on the basis of their similar morphology, the two genera were considered to be synonymous by K. Hauerslev and P. Roberts. in 1970 Svrček & Pouzar introduced the genus ''Cejpomyces'' for a species resembling ''Thanatephorus'', but having septate basidiospores. Based on their similar morphology, the genera were considered synonymous by Langer (1994). In 1971 Talbot & Keane introduced the genus ''Oncobasidium'' for a plant pathogenic species resembling ''Thanatephorus'' but lacking sclerotia and in 1972 M.A. Donk introduced the genus ''Ypsilondium'' for a species resembling ''Uthatobasidium'' but having bisterigmate (two-spored) basidia. Both genera were considered synonyms of ''Thanatephorus'' by Roberts (1999). In 1978 Tu & Kimbrough introduced the genus ''Aquathanatephorus'' for an isolate from water hyacinth

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