Rhizoctonia is agenus offungi in thefamilyCeratobasidiaceae.Species form thin, effused,corticioidbasidiocarps (fruit bodies), but are most frequently found in their sterile,anamorph state.Rhizoctonia species aresaprotrophic, but some are alsofacultativeplant pathogens, causing commercially importantcrop diseases. Some are alsoendomycorrhizal associates oforchids.[1][2] The genus name was formerly used to accommodate many superficially similar, but unrelated fungi. As of 2025, the synonymisation of several genera under a unifiedRhizoctonia was formalised, and the genus now includes names formerly circumscribed underMoniliopsis,Ceratobasidium,Thanatephorus,Uthatobasidium,Koleroga,Cejpomyces,Oncobasidium,Ypsilonidium,Ceratorhiza, andTofispora.[1] As currently circumscribed, the genus contains 52 accepted species.
Rhizoctonia was introduced in 1815 by French mycologistAugustin Pyramus de Candolle foranamorphic plant pathogenic fungi that produce both hyphae andsclerotia. The name is derived from Ancient Greek, ῥίζα (rhiza, "root") + κτόνος (ktonos, "murder"), and de Candolle's original species,Rhizoctonia crocorum (teleomorphHelicobasidium purpureum), is the causal agent of violet root rot ofcarrots and other root vegetables.[3] Subsequent authors added over 100 additional names to the genus, most of them plant pathogens bearing only a superficial resemblance to thetype species.[4]Rhizoctonia thus became an artificialform genus of anamorphic fungi comprising a diverse range of unrelated species.[5]
As part of a move towards a more natural classification of fungi, American mycologistRoyall T. Moore proposed in 1987 thatRhizoctonia should be restricted to thetype species and its relatives, with unrelated species moved to other genera.[6] Unfortunately, this meant that the best-known but unrelated species,Rhizoctonia solani, would have undergone a name change toMoniliopsis solani. To avoid this, it was subsequently proposed thatR. solani should replaceR. crocorum as thetype species ofRhizoctonia. This proposal was passed and the type ofRhizoctonia is now conserved asR. solani under theInternational Code of Nomenclature for algae, fungi, and plants.[7]
R.T. Moore retained species having teleomorphs in the genusThanatephorus withinRhizoctonia, but moved those with teleomorphs in the genusCeratobasidium to the new anamorphic genusCeratorhiza.[6]
In 1956, Dutch mycologistM.A. Donk published the new teleomorphic generaThanatephorus andUthatobasidium simultaneously, reserving the former for plant-pathogenic species producing sclerotia-bearingRhizoctonia anamorphs (withT. cucumeris as the type) and the latter for saprotrophic species not producing anamorphs (withU. fusisporum as the type).[8] In 1996, on the basis of their similar morphology, the two genera were considered to be synonymous by K. Hauerslev and P. Roberts.[9] in 1970 Svrček &Pouzar introduced the genusCejpomyces for a species resemblingThanatephorus, but having septatebasidiospores.[10] Based on their similar morphology, the genera were considered synonymous by Langer (1994).[9] In 1971 Talbot & Keane introduced the genusOncobasidium for a plant pathogenic species resemblingThanatephorus but lacking sclerotia[11] and in 1972 M.A. Donk introduced the genusYpsilondium for a species resemblingUthatobasidium but having bisterigmate (two-spored) basidia.[12] Both genera were considered synonyms ofThanatephorus by Roberts (1999).[9] In 1978 Tu & Kimbrough introduced the genusAquathanatephorus for an isolate fromwater hyacinth which produced a teleomorph with swollen, inwardly curvingsterigmata.[13] This was redetermined asThanatephorus cucumeris by Andersen (1996).[14]
Ceratobasidium was introduced in 1935 by American mycologist D.P. Rogers to accommodate species of the oldform genusCorticium that showed affinities with theheterobasidiomycetes. These affinities were the possession of large sterigmata ("cerato-basidium" means "hornedbasidium") and the production of basidiospores that produce secondary spores.[15] The genusKoleroga was proposed by Donk (1958) to accommodateK. noxia, a plant pathogen morphologically similar toCeratobasidium but not known to produce secondary spores.[16] Talbot (1965) demonstrated that such spores were present in some collections and suggested thatKoleroga be synonymized withCeratobasidium.[9]
Molecular research, based oncladistic analysis ofDNA sequences, placesRhizoctonia within thefamilyCeratobasidiaceae.[17][18] The genus is onlymonophyletic, however, if species ofCeratobasidium (excluding the type)[19] andCeratorhiza are included as synonyms, since there is no apparent distinction between these species and species ofRhizoctonia.[18][19] DNA sequencing has also confirmed the synonymy ofUthatobasidium,Oncobasidium, andKoleroga.[19]
Following changes to theInternational Code of Nomenclature for algae, fungi, and plants, the practice of giving different names to teleomorph and anamorph forms of the same fungus was discontinued, meaning thatThanatephorus became a synonym of the earlier nameRhizoctonia.[19] The problematic application of various anamorph/teleomorph names within Ceratobasidiaceae was rectified in 2025 with the recognition of a unifiedRhizoctonia, formalised by the transfer of 32 names fromMoniliopsis,Ceratobasidium,Thanatephorus,Uthatobasidium,Koleroga,Cejpomyces,Oncobasidium,Ypsilonidium,Ceratorhiza, andTofispora.[1]
The most recent comprehensive review of names inRhizoctonia and allied genera was completed in 2025 by O'Donnell et al.[1] Names previously placed withinRhizoctonia or its generic synonyms that are now placed in other genera are listed below. Refer to O'Donnell et al. (2025)[1] for a summary of 66 invalid/illegitimate names and 34 names of uncertain application (nomina dubia).
Species aresaprotrophic, often occurring in soil and producing basidiocarps (fruit bodies) on dead stems and plant detritus. They are also opportunistic plant pathogens, with an almost unlimited host range, and have been isolated fromorchid mycorrhiza. Distribution appears to becosmopolitan.[9]
Rhizoctonia solani causes a wide range of commercially significant plant diseases. It is one of the fungi responsible forBrown patch (aturfgrass disease),damping off in seedlings, as well as black scurf ofpotatoes,[20] bare patch ofcereals,[21]root rot ofsugar beet,[22] belly rot ofcucumber,[23]sheath blight ofrice,[24] and many other pathogenic conditions.[9]Rhizoctonia oryzae-sativae causes 'aggregate sheath spot' and 'sclerotium' disease of rice.[9] The subtropicalRhizoctonia noxia causes 'black rot' of coffee and other foliar blights,[9] whilstRhizoctonia theobromae causes 'vascular-streak dieback' ofTheobroma cacao (cocoa tree).[25] In Europe,Rhizoctonia butinii causes web blight of spruce.[19][26]
An efficient conversion oftryptophan toindole-3-acetic acid (IAA) and/ortryptophol can be achieved by some species in the genusRhizoctonia.[27]
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