Rhizoctonia

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Rhizoctonia
Rhizoctonia solani.jpg
Disease of cucumber caused by Rhizoctonia solani
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Fungi
Division: Basidiomycota
Class: Agaricomycetes
Order: Cantharellales
Family: Ceratobasidiaceae
Genus: Rhizoctonia
DC. (1815)
Type species
Rhizoctonia solani
J.G. Kühn (1858)
Species
Synonyms

MoniliopsisRuhland (1908)
ThanatephorusDonk (1956)
UthatobasidiumDonk (1956)
KolerogaDonk (1958)
CejpomycesSvrcek & Pouzar (1970)
OncobasidiumTalbot & Keane (1971)
YpsilondiumDonk (1972)
AquathanatephorusTu & Kimbrough (1978)
CeratorhizaR.T. Moore (1987)

Contents

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. [1] 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. [2] Subsequent authors added over 100 additional names to the genus, most of them plant pathogens bearing only a superficial resemblance to the type species. [3] Rhizoctonia thus became an artificial form genus of anamorphic fungi comprising a diverse range of unrelated species. [4]

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. [5] 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. [6]

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. [5]

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). [7] In 1996, on the basis of their similar morphology, the two genera were considered to be synonymous by K. Hauerslev and P. Roberts. [8] in 1970 Svrček & Pouzar introduced the genus Cejpomyces for a species resembling Thanatephorus, but having septate basidiospores. [9] Based on their similar morphology, the genera were considered synonymous by Langer (1994). [8] In 1971 Talbot & Keane introduced the genus Oncobasidium for a plant pathogenic species resembling Thanatephorus but lacking sclerotia [10] and in 1972 M.A. Donk introduced the genus Ypsilondium for a species resembling Uthatobasidium but having bisterigmate (two-spored) basidia. [11] Both genera were considered synonyms of Thanatephorus by Roberts (1999). [8] In 1978 Tu & Kimbrough introduced the genus Aquathanatephorus for an isolate from water hyacinth which produced a teleomorph with swollen, inwardly curving sterigmata. [12] This was redetermined as Thanatephorus cucumeris by Andersen (1996). [13]

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. [14] 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. [15] Talbot (1965) demonstrated that such spores were present in some collections and suggested that Koleroga be synonymized with Ceratobasidium. [8]

Current status

Molecular research, based on cladistic analysis of DNA sequences, places Rhizoctonia within the family Ceratobasidiaceae. [16] [17] The genus is only monophyletic, however, if species of Ceratobasidium (excluding the type) [18] and Ceratorhiza are included as synonyms, since there is no apparent distinction between these species and species of Rhizoctonia. [17] [18] DNA sequencing has also confirmed the synonymy of Uthatobasidium, Oncobasidium, and Koleroga. [18]

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. [18] 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. [4] Only a few frequently used names are listed below. Many older names are of uncertain application or were never validly published, or both. [4]

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. [8]

Economic importance

Rhizoctonia solani causes a wide range of commercially significant plant diseases. It is one of the fungi responsible for Brown patch (a turfgrass disease), damping off in seedlings, as well as black scurf of potatoes, [20] bare patch of cereals, [21] root rot of sugar beet, [22] belly rot of cucumber, [23] sheath blight of rice, [24] and many other pathogenic conditions. [8] Rhizoctonia oryzae-sativae causes 'aggregate sheath spot' and 'sclerotium' disease of rice. [8] The subtropical Rhizoctonia noxia causes 'black rot' of coffee and other foliar blights, [8] whilst Rhizoctonia theobromae causes 'vascular-streak dieback' of Theobroma cacao (cocoa tree). [25] In Europe, Rhizoctonia butinii causes web blight of spruce. [18] [26]

An efficient conversion of tryptophan to indole-3-acetic acid (IAA) and/or tryptophol can be achieved by some species in the genus Rhizoctonia. [27]

Related Research Articles

<span class="mw-page-title-main">Cantharellales</span> Order of fungi

The Cantharellales are an order of fungi in the class Agaricomycetes. The order includes not only the chanterelles (Cantharellaceae), but also some of the tooth fungi (Hydnaceae), clavarioid fungi, and corticioid fungi (Botryobasidiaceae). Species within the order are variously ectomycorrhizal, saprotrophic, associated with orchids, or facultative plant pathogens. Those of economic importance include edible and commercially collected Cantharellus, Craterellus, and Hydnum species as well as crop pathogens in the genera Ceratobasidium and Thanatephorus/Rhizoctonia.

<i>Trichoderma viride</i> Species of fungus

Trichoderma viride is a fungus and a biofungicide.

<i>Rhizoctonia solani</i> Species of fungus

Rhizoctonia solani is a species of fungus in the order Cantharellales. Basidiocarps are thin, effused, and web-like, but the fungus is more typically encountered in its anamorphic state, as hyphae and sclerotia. The name Rhizoctonia solani is currently applied to a complex of related species that await further research. In its wide sense, Rhizoctonia solani is a facultative plant pathogen with a wide host range and worldwide distribution. It causes various plant diseases such as root rot, damping off, and wire stem. It can also form mycorrhizal associations with orchids.

<span class="mw-page-title-main">Damping off</span> Horticultural disease or condition

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.

<i>Helicobasidium purpureum</i> Species of fungus

Helicobasidium purpureum is a species of fungus in the subdivision Pucciniomycotina. Basidiocarps are corticioid (patch-forming) and are typically violet to purple. Microscopically they have auricularioid basidia. Helicobasidium purpureum is an opportunistic plant pathogen and is one of the causes of violet root rot of crops and other plants. DNA sequencing suggests that it is a complex of more than one species. The species has a conidia-bearing anamorph in the Tuberculina persicina complex that is a parasite of rust fungi.

<i>Ceratobasidium cornigerum</i> Species of fungus

Ceratobasidium cornigerum is a species of fungus in the order Cantharellales. Basidiocarps are thin, spread on the substrate out like a film (effused) and web-like. An anamorphic state is frequently obtained when isolates are cultured. Ceratobasidium cornigerum is saprotrophic, but is also a facultative plant pathogen, causing a number of economically important crop diseases, and an orchid endomycorrhizal associate. The species is genetically diverse and is sometimes treated as a complex of closely related taxa. DNA research shows the species actually belongs within the genus Rhizoctonia.

Magnaporthe salvinii is a fungus known to attack a variety of grass and rice species, including Oryza sativa and Zizania aquatica. Symptoms of fungal infection in plants include small, black, lesions on the leaves that develop into more widespread leaf rot, which then spreads to the stem and causes breakage. As part of its life cycle, the fungus produces sclerotia that persist in dead plant tissue and the soil. Management of the fungus may be effected by tilling the soil, reducing its nitrogen content, or by open field burning, all of which reduce the number of sclerotia, or by the application of a fungicide.

Rhizoctonia noxia is a species of fungus in the order Cantharellales. Basidiocarps 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-roga" or black rot of coffee and various blights of citrus and other trees.

<span class="mw-page-title-main">Corticiaceae</span> Family of fungi

The Corticiaceae are a family of fungi in the order Corticiales. The family formerly included almost all the corticioid fungi, whether they were related or not, and as such was highly artificial. In its current sense, however, the name Corticiaceae is restricted to a comparatively small group of corticioid genera within the Corticiales.

<i>Typhula</i> Genus of fungi

Typhula is a genus of clavarioid fungi in the order Agaricales. Species of Typhula are saprotrophic, mostly decomposing leaves, twigs, and herbaceous material. Basidiocarps are club-shaped or narrowly cylindrical and are simple, often arising from sclerotia. A few species are facultative plant pathogens, causing a number of commercially important crop and turfgrass diseases.

<i>Macrotyphula</i> Genus of fungi

Macrotyphula is a genus of clavarioid fungi in the family Phyllotopsidaceae. Basidiocarps are simple, narrowly club-shaped to filiform, sometimes arising from a sclerotium. They typically grow on dead wood or leaf litter, often in swarms.

<i>Ceratobasidium</i> Genus of fungi

Ceratobasidium is a genus of fungi in the order Cantharellales. Basidiocarps are effused and the genus is sometimes grouped among the corticioid fungi, though species also retain features of the heterobasidiomycetes. Anamorphic forms were formerly referred to the genus Ceratorhiza, but this is now considered a synonym of Rhizoctonia. Ceratobasidium species, excluding the type, are also now considered synonymous with Rhizoctonia and some species have been transferred to the latter genus. Species are saprotrophic, but several are also facultative plant pathogens, causing a number of commercially important crop diseases. Some are also endomycorrhizal associates of orchids.

<span class="mw-page-title-main">Ceratobasidiaceae</span> Family of fungi

The Ceratobasidiaceae are a family of fungi in the order Cantharellales. All species within the family have basidiocarps that are thin and effused. They have sometimes been included within the corticioid fungi or alternatively within the "heterobasidiomycetes". Species are saprotrophic, but some are also facultative plant pathogens or are associated with orchid mycorrhiza. Genera of economic importance include Ceratobasidium and Rhizoctonia, both of which contain plant pathogenic species causing diseases of commercial crops and turf grass.

<span class="mw-page-title-main">Punctulariaceae</span> Family of fungi

The Punctulariaceae are a family of fungi in the order Corticiales. The family in its current sense is based on molecular research and contains just three genera of corticioid fungi.

<i>Tulasnella</i> Genus of fungi

Tulasnella is a genus of effused (patch-forming) fungi in the order Cantharellales. Basidiocarps, when visible, are typically smooth, ceraceous (waxy) to subgelatinous, frequently lilaceous to violet-grey, and formed on the underside of fallen branches and logs. They are microscopically distinct in having basidia with grossly swollen sterigmata on which basidiospores are formed. One atypical species, Tulasnella aurantiaca, produces orange to red, gelatinous, pustular anamorphs on wood. Some species form facultative mycorrhizas with orchids and liverworts. Around 80 species of Tulasnella are known worldwide.

<i>Helicobasidium</i> Genus of fungi


Helicobasidium is a genus of fungi in the subdivision Pucciniomycotina. Basidiocarps are corticioid (patch-forming) and are typically violet to purple. Microscopically they have auricularioid basidia. Asexual anamorphs, formerly referred to the genus Thanatophytum, produce sclerotia. Conidia-bearing anamorphs are parasitic on rust fungi and are currently still referred to the genus Tuberculina.

<i>Botryobasidium</i> Genus of fungi

Botryobasidium is a genus of corticioid fungi belonging to the order Cantharellales. Basidiocarps are ephemeral and typically form thin, web-like, white to cream, effused patches on the underside of fallen branches, logs, and leaf litter. Several species form anamorphs producing chlamydospores. All species are wood- or litter-rotting saprotrophs and the genus has a worldwide distribution.

<i>Agroathelia</i> Genus of fungi

Agroathelia is a fungal genus currently consisting of one widespread and two other species. Agroathelia rolfsii, the type species, causes serious diseases of cultivated crops such as tomatoes, potatoes, peanuts, bell peppers, and sweet potatoes among many other hosts. It is better known under the names Sclerotium rolfsii or Athelia rolfsii.

<i>Agroathelia rolfsii</i> Pathogen fungus

Agroathelia rolfsii is a corticioid fungus in the order Amylocorticiales. It is a facultative plant pathogen and is the causal agent of "southern blight" disease in crops.

References

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  27. 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)