''Rhizoctonia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Cantharellales.

Species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

form thin, effused,

corticioid The corticioid fungi are a group of fungi in the Basidiomycota typically having effused, smooth basidiocarps (fruit bodies) that are formed on the undersides of dead tree trunks or branches. They are sometimes colloquially called crust fungi or p ...

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 not ...

(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 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. Along with the Asteraceae, they are one of the two largest families of flowering ...

. 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 Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 September 1841) was a Swiss botanist. René Louiche Desfontaines launched de Candolle's botanical career by recommending him at a herbarium. Within a couple of years 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 In 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 species that contains the biological type specimen( ...

. ''Rhizoctonia'' thus became an artificial

form genus Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of s ...

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 Royall Tyler Moore (October 11, 1930 – August 17, 2014) was an American-born mycologist and mycology professor. Education and work He received his doctorate from the Harvard University in 1959, writing his dissertation on the fungal genus '' Sp ...

proposed in 1987 that ''Rhizoctonia'' should be restricted to the

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

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) 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 those "trad ...

. 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 A basidiospore is a reproductive spore produced by Basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are ...

. 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 outside its native range.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

'' Corticium'' that showed affinities with the heterobasidiomycetes. These affinities were the possession of large sterigmata ("cerato-basidium" means "horned

basidium A basidium () is a microscopic sporangium (a spore-producing structure) found on the hymenophore of fruiting bodies of basidiomycete fungi which are also called tertiary mycelium, developed from secondary mycelium. Tertiary mycelium is hig ...

") 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 held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

research, based on

cladistic Cladistics (; ) 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 typically shared derived ch ...

analysis of

DNA sequences A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are usu ...

, places ''Rhizoctonia'' within the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Ceratobasidiaceae. The genus is only

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. 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

, 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.

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'' ( Botryosphaeriaceae) *''Rhizoctonia carotae'' = ''

Athelia arachnoidea ''Athelia arachnoidea'' is a corticioid fungus in the family Atheliaceae. The species forms thin, white, cobwebby basidiocarps (fruit bodies) and typically occurs saprotrophically on leaf litter and fallen wood. It can, however, also be a facult ...

'' (

Atheliaceae Atheliaceae is a family of corticioid fungi placed under the monotypic order Atheliales. Both the order and the family were described by Walter Jülich in 1981. According to a 2008 estimate, the family contains 20 genera and approximately 100 spe ...

) *''Rhizoctonia crocorum'' = '' Helicobasidium purpureum'' (

Helicobasidiaceae The Helicobasidiales are an order of rust fungi in the class Pucciniomycetes. It contains the single family Helicobasidiaceae, which itself comprises three genera: ''Helicobasidium'', '' Stypinella'', and ''Tuberculina''. Helicobasidiales was ci ...

) *''Rhizoctonia leguminicola'' = '' Botrytis fabae'' ( Sclerotiniaceae) *''Rhizoctonia oryzae'' = not a validly published name but now validated as '' Waitea oryzae'' ( Corticiaceae) *''Rhizoctonia rubi'' = not a validly published name and of uncertain application (probably

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 de ...

) *''Rhizoctonia zeae'' = '' Waitea zeae'' ( Corticiaceae)

Habitat and distribution

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.

Economic importance

'' Rhizoctonia solani'' causes a wide range of commercially significant plant diseases. It is one of the fungi responsible for

Brown patch Brown patch is a common turfgrass fungal disease that is caused by species in the genus ''Rhizoctonia'', usually ''Rhizoctonia solani''. Brown patch can be found in all of the cool season turfgrasses found in the United States. Brown patch is most ...

(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 a ...

in seedlings, as well as black scurf of

potatoes The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern United ...

, bare patch of

cereals A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more foo ...

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. It is found in both indoor and outdoor plants, althoug ...

sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet ('' Beta vulgaris''). Together ...

, belly rot of

cucumber Cucumber (''Cucumis sativus'') is a widely-cultivated creeping vine plant in the Cucurbitaceae family that bears usually cylindrical fruits, which are used as culinary vegetables. sheath blight of

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly '' Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and ''Porteresia'', both wild and domestica ...

, and many other pathogenic conditions. ''

Rhizoctonia oryzae-sativae ''Ceratobasidium setariae'' is a fungal plant pathogen. References External links Fungal plant pathogens and diseases Cantharellales Fungi described in 1986 {{fungus-plant-disease-stub ...

'' causes 'aggregate sheath spot' and 'sclerotium' disease of rice. The subtropical ''

Rhizoctonia noxia ''Rhizoctonia noxia'' is a species of fungus in the order Cantharellales. Basidiocarps (fruit bodies) are thin, effused, and web-like. The species is tropical to sub-tropical and is mainly known as a plant pathogen, the causative agent of "kole-r ...

'' causes 'black rot' of coffee and other foliar blights, whilst ''

Rhizoctonia theobromae ''Rhizoctonia theobromae'' is a species of fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These org ...

'' causes 'vascular-streak dieback' of ''

Theobroma cacao ''Theobroma cacao'', also called the cacao tree and the cocoa tree, is a small ( tall) evergreen tree in the family Malvaceae. Its seeds, cocoa beans, are used to make chocolate liquor, cocoa solids, cocoa butter and chocolate. The largest ...

'' (cocoa tree). In Europe, ''

Rhizoctonia butinii ''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, bu ...

'' 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 aromati ...

to indole-3-acetic acid (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

References

External links

Index Fungorum
* {{Taxonbar, from=Q2716477 Cantharellales Fungal plant pathogens and diseases Agaricomycetes genera