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 which produced a teleomorph with swollen, inwardly curving
sterigmata. This was redetermined as
Thanatephorus cucumeris by Andersen (1996).
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. The genus
Koleroga was proposed by Donk (1958) to accommodate
K. noxia, a plant pathogen morphologically similar to
Ceratobasidium but not known to produce secondary spores. Talbot (1965) demonstrated that such spores were present in some collections and suggested that
Koleroga be synonymized with
Ceratobasidium.
Current status Molecular research, based on
cladistic analysis of
DNA sequences, places
Rhizoctonia within the
family Ceratobasidiaceae. The genus is only
monophyletic, however, if species of
Ceratobasidium (excluding the type) and
Ceratorhiza are included as synonyms, since there is no apparent distinction between these species and species of
Rhizoctonia. DNA sequencing has also confirmed the synonymy of
Uthatobasidium,
Oncobasidium, and
Koleroga. Following changes to the
International 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 that
Thanatephorus became a synonym of the earlier name
Rhizoctonia. The problematic application of various anamorph/teleomorph names within Ceratobasidiaceae was rectified in 2025 with the recognition of a unified
Rhizoctonia, formalised by the transfer of 32 names from
Moniliopsis,
Ceratobasidium,
Thanatephorus,
Uthatobasidium,
Koleroga,
Cejpomyces,
Oncobasidium,
Ypsilonidium,
Ceratorhiza, and
Tofispora.
Redisposition of former species The most recent comprehensive review of names in
Rhizoctonia and allied genera was completed in 2025 by O'Donnell et al. Names previously placed within
Rhizoctonia or its generic synonyms that are now placed in other genera are listed below. Refer to O'Donnell et al. (2025) for a summary of 66 invalid/illegitimate names and 34 names of uncertain application (nomina dubia). •
Cejpomyces globosisporus =
Botryobasidium globisporum (
Botryobasidiaceae) •
Ceratobasidium atratum =
Scotomyces subviolaceus (
Hydnaceae) •
Ceratobasidium fibrillosum =
Oliveonia fibrillosa (
Oliveoniaceae) •
Ceratobasidium mycophagum =
Syzygospora mycophaga (
Filobasidiaceae) •
Ceratobasidium pearsonii =
Paullicorticium pearsonii (
Hydnaceae) •
Ceratobasidium plumbeum =
Scotomyces subviolaceus (
Hydnaceae) •
Ceratobasidium striisporum =
Xenasma pulverulentum (
Xenasmataceae) •
Ceratobasidium subatratum =
Scotomyces subviolaceus (
Hydnaceae) •
Ceratobasidium vagum =
Botryobasidium vagum (
Botryobasidiaceae) •
Rhizoctonia allii =
Helicobasidium purpureum (
Helicobasidiaceae) •
Rhizoctonia anaticula =
Tulasnella anaticula (
Tulasnellaceae) •
Rhizoctonia asparagi =
Helicobasidium purpureum (
Helicobasidiaceae) •
Rhizoctonia bataticola =
Macrophomina phaseolina (
Botryosphaeriaceae) •
Rhizoctonia carotae =
Athelia arachnoidea (
Atheliaceae) •
Rhizoctonia centrifuga =
Athelia epiphylla (
Atheliaceae) •
Rhizoctonia crocorum =
Helicobasidium purpureum (
Helicobasidiaceae) •
Rhizoctonia lamellifera =
Macrophomina phaseolina (
Botryosphaeriaceae) •
Rhizoctonia leguminicola =
Slafractonia leguminicola (
Incertae sedis;
Ascomycota) •
Rhizoctonia medicaginis =
Helicobasidium purpureum (
Helicobasidiaceae) •
Rhizoctonia menthae =
Puccinia menthae (
Pucciniaceae) •
Rhizoctonia orobanches =
Urocystis orobanches (
Urocystidaceae) •
Rhizoctonia quercina =
Rosellinia quercina (
Xylariaceae) •
Rhizoctonia repens =
Tulasnella deliquescens (
Tulasnellaceae) •
Rhizoctonia rubiae =
Helicobasidium purpureum (
Helicobasidiaceae) •
Rhizoctonia solani f. paroketea =
Agroathelia rolfsii (
Amylocorticiaceae) •
Rhizoctonia tabifica =
Colletotrichum coccodes (
Glomerellaceae) •
Rhizoctonia zeae =
Waitea zeae (
Corticiaceae) •
Uthatobasidium citriforme =
Sistotrema citriforme (
Hydnaceae) ==Habitat and distribution==