Rhizoctonia
Encyclopedia
Rhizoctonia is a genus
of anamorphic fungi in the order
Cantharellales
. Species
do not produce spores, but are composed of hyphae and sclerotia
(hyphal propagules) and are asexual states of fungi in the genus Thanatephorus. Rhizoctonia species are saprotrophic, but are also facultative
plant pathogens, causing commercially important crop diseases. They are also endomycorrhizal
associates of orchids. The genus name was formerly used to accommodate many superficially similar, but unrelated fungi.
. Rhizoctonia thus became an artificial form genus comprising a diverse range of unrelated species.
As part of a move towards a more natural classification of fungi, R.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
(teleomorph Thanatephorus cucumeris), 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 Botanical Nomenclature.
Ceratobasidiaceae
.
. Distribution appears to be cosmopolitan
.
causes a wide range of commercially significant plant diseases. It is one of the fungi responsible for damping off
in seedlings, as well as black scurf of potatoes, bare patch of cereals, root rot
of sugar beet
, belly rot of cucumber
, sheath blight
of rice
, and many other pathogenic conditions.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of anamorphic fungi in the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Cantharellales
Cantharellales
The Cantharellales are an order of fungi in the class Agaricomycetes. The order includes not only the chanterelles , but also some of the tooth fungi , clavarioid fungi , and corticioid fungi...
. Species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
do not produce spores, but are composed of hyphae and sclerotia
Sclerotium
A sclerotium is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until a favorable opportunity for growth. Other fungi that produce...
(hyphal propagules) and are asexual states of fungi in the genus Thanatephorus. Rhizoctonia species are saprotrophic, but are also facultative
Facultative parasite
A facultative parasite is an organism that may resort to parasitic activity, but does not absolutely rely on any host for completion of its life cycle....
plant pathogens, causing commercially important crop diseases. They are also endomycorrhizal
Orchid mycorrhiza
Orchid mycorrhizae are symbiotic relationships between the roots of plants of the family Orchidaceae and a variety of fungi. All orchids are myco-heterotrophic at some point in their life cycle. Orchid mycorrhizae are critically important during orchid germination, as orchid seed has virtually no...
associates of orchids. The genus name was formerly used to accommodate many superficially similar, but unrelated fungi.
History
Rhizoctonia was introduced in 1815 by French mycologist Augustin Pyramus de Candolle for plant pathogenic fungi that produce both hyphae and sclerotia. "Rhizoctonia" means "root killer" 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 speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
. Rhizoctonia thus became an artificial form genus comprising a diverse range of unrelated species.
As part of a move towards a more natural classification of fungi, R.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
Rhizoctonia solani
Rhizoctonia solani is a plant pathogenic fungus with a wide host range and worldwide distribution. This plant pathogen was discovered more than 100 years ago. Rhizoctonia solani frequently exists as thread-like growth on plants or in culture. Asexual spores are not produced, only the sexual stage...
(teleomorph Thanatephorus cucumeris), 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
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of Rhizoctonia. This proposal was passed and the type of Rhizoctonia is now conserved as R. solani under the International Code of Botanical Nomenclature.
Current status
In its current sense, the genus is effectively restricted to the type species Rhizoctonia solani and its synonyms. The genus name is still, however, widely used in its old, artificial sense. Molecular research, based on cladistic analysis of DNA sequences, places Rhizoctonia within the familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Ceratobasidiaceae
Ceratobasidiaceae
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...
.
Redisposition of former species
A comprehensive survey and redisposition of 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 phaseolinaMacrophomina phaseolinaMacrophomina phaseolina is a Botryosphaeriaceae fungus that is a plant pathogen that causes charcoal rot on many plant species including Zea mays and Pinus elliottii.- External links :* *...
(BotryosphaeriaceaeBotryosphaeriaceaeThe Botryosphaeriaceae are a family of sac fungi. It is the only representative of the order Botryosphaeriales. According to a 2008 estimate, the family contains 26 genera and over 1500...
) - Rhizoctonia carotae = Fibulorhizoctonia carotae (teleomorph Athelia arachnoideaAthelia arachnoideaAthelia arachnoidea is a corticioid fungus in the family Atheliaceae. The species forms thin, white, cobwebby basidiocarps and typically occurs saprotrophically on leaf litter and fallen wood...
)(AtheliaceaeAtheliaceaeThe Atheliaceae are a family of fungi in the monotypic order Atheliales. Both the order and the family were described by W. Jülich in 1981. According to a 2008 estimate, the family contains 22 genera and 106 species.-Genera:*Amphinema...
) - Rhizoctonia cerealis = not a validly published name (teleomorph Ceratobasidium cerealeCeratobasidium cerealeCeratobasidium cereale is a plant pathogen.- External links :* *...
) (CeratobasidiaceaeCeratobasidiaceaeThe 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...
) - Rhizoctonia crocorum = Thanatophytum crocorum (teleomorph Helicobasidium purpureum) (HelicobasidiaceaeHelicobasidiaceaeHelicobasidiaceae is a family of fungus in the order Helicobasidiales. It contains two genera....
) - Rhizoctonia fragariae = not a validly published name (teleomorph Ceratobasidium cornigerumCeratobasidium cornigerumCeratobasidium cornigerum is a species of fungus in the order Cantharellales. Basidiocarps are thin, spread on the substrate out like a film and web-like. A Rhizoctonia-like anamorphic state, sometimes referred to the genus Ceratorhiza, is frequently obtained when isolates are cultured...
) (CeratobasidiaceaeCeratobasidiaceaeThe 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...
) - Rhizoctonia goodyerae-repentis = a name of uncertain application, but generally interpreted as Ceratobasidium cornigerumCeratobasidium cornigerumCeratobasidium cornigerum is a species of fungus in the order Cantharellales. Basidiocarps are thin, spread on the substrate out like a film and web-like. A Rhizoctonia-like anamorphic state, sometimes referred to the genus Ceratorhiza, is frequently obtained when isolates are cultured...
(CeratobasidiaceaeCeratobasidiaceaeThe 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...
) - Rhizoctonia leguminicola = Botrytis fabaeBotrytis fabaeBotrytis fabae is a plant pathogen, a fungus that causes chocolate spot disease of broad or fava bean plants, Vicia faba.-Symptoms:...
(Sclerotiniaceae) - Rhizoctonia oryzae = not a validly published name and of uncertain application, but generally interpreted as Waitea circinataWaitea circinataWaitea circinata is a species of fungus in the family Corticiaceae. Basidiocarps are thin, effused, and web-like, but the fungus is more frequently encountered in its similar but sterile anamorphic state, sometimes called Rhizoctonia zeae...
(CorticiaceaeCorticiaceaeThe 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...
) - Rhizoctonia ramicola = Ceratorhiza ramicola (teleomorph Ceratobasidium ramicolaCeratobasidium ramicolaCeratobasidium ramicola is a plant pathogen.- External links :* *...
) (CeratobasidiaceaeCeratobasidiaceaeThe 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...
) - Rhizoctonia rubi = not a validly published name and of uncertain application (probably AscomycotaAscomycotaThe Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac fungi. They are the largest phylum of Fungi, with over 64,000 species...
) - Rhizoctonia zeae = Waitea circinataWaitea circinataWaitea circinata is a species of fungus in the family Corticiaceae. Basidiocarps are thin, effused, and web-like, but the fungus is more frequently encountered in its similar but sterile anamorphic state, sometimes called Rhizoctonia zeae...
(CorticiaceaeCorticiaceaeThe 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...
)
Habitat and distribution
Species are saprotrophic, occurring in the soil and producing basidiocarps (fruit bodies of the Thanatephorus teleomorph) on dead stems and plant detritus. They are also opportunistic plant pathogens, with an almost unlimited host range, and have been isolated from orchid mycorrhizaOrchid mycorrhiza
Orchid mycorrhizae are symbiotic relationships between the roots of plants of the family Orchidaceae and a variety of fungi. All orchids are myco-heterotrophic at some point in their life cycle. Orchid mycorrhizae are critically important during orchid germination, as orchid seed has virtually no...
. Distribution appears to be cosmopolitan
Cosmopolitan distribution
In biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
.
Economic importance
Rhizoctonia solaniRhizoctonia solani
Rhizoctonia solani is a plant pathogenic fungus with a wide host range and worldwide distribution. This plant pathogen was discovered more than 100 years ago. Rhizoctonia solani frequently exists as thread-like growth on plants or in culture. Asexual spores are not produced, only the sexual stage...
causes a wide range of commercially significant plant diseases. It is one of the fungi responsible for damping off
Damping off
Damping off is the term used for a number of different fungus-caused ailments that can kill seeds or seedlings before or after they germinate....
in seedlings, as well as black scurf of potatoes, bare patch of cereals, root rot
Root rot
Root rot is a condition found in both indoor and outdoor plants, although more common in indoor plants with poor drainage. As the name states, the roots of the plant rot. Usually, this is a result of overwatering. In houseplants, it is a very common problem, and is slightly less common in outdoor...
of sugar beet
Sugar beet
Sugar beet, a cultivated plant of Beta vulgaris, is a plant whose tuber contains a high concentration of sucrose. It is grown commercially for sugar production. Sugar beets and other B...
, belly rot of cucumber
Cucumber
The cucumber is a widely cultivated plant in the gourd family Cucurbitaceae, which includes squash, and in the same genus as the muskmelon. The plant is a creeping vine which bears cylindrical edible fruit when ripe. There are three main varieties of cucumber: "slicing", "pickling", and...
, sheath blight
Blight
Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. It is simply a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this...
of rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
, and many other pathogenic conditions.