genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
fungi
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
in the
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
basidiocarps
In fungi, a basidiocarp, basidiome, or basidioma () is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do no ...
orchids
Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Orchids are cosmopolitan plants that are found in almost every habitat on Earth ...
. The genus name was formerly used to accommodate many superficially similar, but unrelated fungi.
''Rhizoctonia'' was introduced in 1815 by French mycologist
Augustin Pyramus de Candolle
Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 September 1841) was a Swiss people, Swiss botany, botanist. René Louiche Desfontaines launched de Candolle's botanical career by recommending him at a herbarium. Within a couple ...
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
The carrot (''Daucus carota'' subsp. ''sativus'') is a root vegetable, typically orange in colour, though heirloom variants including purple, black, red, white, and yellow cultivars exist, all of which are domesticated forms of the Daucus ...
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
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
. ''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
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
and its relatives, with unrelated species moved to other genera. Unfortunately, this meant that the best-known but unrelated species, ''
Rhizoctonia solani
''Rhizoctonia solani'' is a species of fungus in the order Cantharellales. Basidiocarps (fruit bodies) are thin, effused, and web-like, but the fungus is more typically encountered in its anamorphic state, as hyphae and sclerotia. The name ' ...
'', 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
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
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
The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...
.
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''.
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
''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth, is an aquatic plant native to South America, naturalized throughout the world, and often invasive species, invasive outside its native rang ...
which produced a teleomorph with swollen, inwardly curving
sterigmata
In biology, a sterigma (: sterigmata) is a small supporting structure.
It commonly refers to an extension of the basidium (the spore-bearing cells) consisting of a basal filamentous part and a slender projection which carries a spore at the tip ...
. 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
A basidium (: basidia) is a microscopic spore-producing structure found on the hymenophore of reproductive bodies of basidiomycete fungi. The presence of basidia is one of the main characteristic features of the group. These bodies are also ...
") 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
A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...
research, based on
cladistic
Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...
analysis of
DNA sequences
A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the ...
, places ''Rhizoctonia'' within the
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
monophyletic
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent co ...
, 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 ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...
, 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''. In its current sense, therefore, the genus ''Rhizoctonia'' includes both anamorphic and teleomorphic fungi. Not all species referred to ''Ceratobasidium'' or ''Thanatephorus'' have yet been combined in ''Rhizoctonia'', however.
Redisposition of former species
A comprehensive survey and redisposition of old species names in ''Rhizoctonia'' was published in 1994 by Andersen & Stalpers. Only a few frequently used names are listed below. Many older names are of uncertain application or were never validly published, or both.
*''Rhizoctonia bataticola'' = ''
Macrophomina phaseolina
''Macrophomina phaseolina'' is a Botryosphaeriaceae plant pathogen fungus that causes damping off, seedling blight, collar rot, stem rot, charcoal rot, basal stem rot, and root rot on many plant species.
Hosts, symptoms, and signs
One of th ...
Ascomycota
Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...
Species are saprotrophic, 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 from orchid mycorrhiza. Distribution appears to be
cosmopolitan
Cosmopolitan may refer to:
Internationalism
* World citizen, one who eschews traditional geopolitical divisions derived from national citizenship
* Cosmopolitanism, the idea that all of humanity belongs to a single moral community
* Cosmopolitan ...
.
Economic importance
''
Rhizoctonia solani
''Rhizoctonia solani'' is a species of fungus in the order Cantharellales. Basidiocarps (fruit bodies) are thin, effused, and web-like, but the fungus is more typically encountered in its anamorphic state, as hyphae and sclerotia. The name ' ...
'' causes a wide range of commercially significant plant diseases. It is one of the fungi responsible for Brown patch (a turfgrass disease),
damping off
Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions.
Symptoms
There ar ...
in seedlings, as well as black scurf of
potatoes
The potato () is a starchy tuberous vegetable native to the Americas that is consumed as a staple food in many parts of the world. Potatoes are underground stem tubers of the plant ''Solanum tuberosum'', a perennial in the nightshade famil ...
, bare patch of
cereals
A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize (Corn). Edible grains from other plant families, suc ...
,
root rot
Root rot is a condition in which anoxic conditions in the soil or potting media around the roots of a plant cause them to rot. This occurs due to excessive standing water around the roots.-Hydroponics Root Rot: What is It, How To Treat It, How ...
of
sugar beet
A sugar beet is a plant whose root contains a high concentration of sucrose and that is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together with ...
, belly rot of
cucumber
The cucumber (''Cucumis sativus'') is a widely-cultivated creeping vine plant in the family Cucurbitaceae that bears cylindrical to spherical fruits, which are used as culinary vegetables.
sheath blight
Rice-sheath blight is a disease caused by ''Rhizoctonia solani'' (Teleomorph, anamorph and holomorph, teleomorph is ''Thanetophorus cucumeris''), a Basidiomycota, basidiomycete, that causes major limitations on rice production in India and other ...
of
rice
Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...
, and many other pathogenic conditions. '' Rhizoctonia oryzae-sativae'' causes 'aggregate sheath spot' and 'sclerotium' disease of rice. The subtropical '' Rhizoctonia noxia'' causes 'black rot' of coffee and other foliar blights, whilst '' Rhizoctonia theobromae'' causes 'vascular-streak dieback' of ''
Theobroma cacao
''Theobroma cacao'' (cacao tree or cocoa tree) is a small ( tall) evergreen tree in the Malvaceae family. Its seedscocoa beansare used to make chocolate liquor, cocoa solids, cocoa butter and chocolate. Although the tree is native to the tropi ...
'' (cocoa tree). In Europe, '' Rhizoctonia butinii'' causes web blight of spruce.
An efficient conversion of
tryptophan
Tryptophan (symbol Trp or W)
is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromat ...
to
indole-3-acetic acid
Indole-3-acetic acid (IAA, 3-IAA) is the most common naturally occurring plant hormone of the auxin class. It is the best known of the auxins, and has been the subject of extensive studies by plant physiologists. IAA is a derivative of indole, con ...
(IAA) and/or tryptophol can be achieved by some species in the genus ''Rhizoctonia''.Efficient Conversion of L-Tryptophan to Indole-3-Acetic Acid and/or Tryptophol by Some Species of Rhizoctonia. Toshiko Furukawa, Jinichiro Koga, Takashi Adachi, Kunihei Kishi and Kunihiko Syono, Plant Cell Physiol., 1996, volume 37, issue 7, pages 899-905 abstract