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A sclerotium (; (), is a compact mass of hardened fungal
mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...
containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher
fungi 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 organisms are classified as a kingdom, separately fr ...
such as
ergot Ergot ( ) or ergot fungi refers to a group of fungi of the genus ''Claviceps''. The most prominent member of this group is '' Claviceps purpurea'' ("rye ergot fungus"). This fungus grows on rye and related plants, and produces alkaloids that c ...
, sclerotia become detached and remain dormant until favorable growth conditions return. Sclerotia initially were mistaken for individual organisms and described as separate species until
Louis René Tulasne Louis René Étienne Tulasne, a.k.a. Edmond Tulasne (12 September 1815 – 22 December 1885) was a French botanist and mycologist born in Azay-le-Rideau. He originally studied law at Poitiers, but his interest later turned to botany. As a youn ...
proved in 1853 that sclerotia are only a stage in the life cycle of some fungi. Further investigation showed that this stage appears in many fungi belonging to many diverse groups. Sclerotia are important in the understanding of the life cycle and reproduction of fungi, as a food source, as medicine (for example,
ergotamine Ergotamine, sold under the brand names Cafergot (with caffeine) and Ergomar among others, is an ergopeptine and part of the ergot family of alkaloids; it is structurally and biochemically closely related to ergoline. It possesses structural sim ...
), and in agricultural
blight Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. Description Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral orga ...
management. Examples of fungi that form sclerotia are ergot ('' Claviceps purpurea''), ''
Polyporus tuberaster ''Polyporus tuberaster'' is a species of fungus in the genus ''Polyporus''. The yellow-brown cap A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 32 ...
'', '' Psilocybe mexicana'', '' Sclerotium delphinii'' and many species in Sclerotiniaceae. Although not fungal, the
plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a ve ...
of
slime mold Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms with a life cycle that includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic mul ...
s can form sclerotia in adverse environmental conditions.


Description

Sclerotia are often composed of a thick, dense shell with thick and dark cells and a core of thin colorless cells. Sclerotia are rich in hyphae emergency supplies, especially oil. They contain a very small amount of water (5–10%) and can survive in a dry environment for several years without losing the ability to grow. In most cases, the sclerotium consists exclusively of fungal hyphae, whereas some may consist partly of fungal hyphae plexus and partly in between tissues of the substrate (ergot, Sclerotinia). In favorable conditions, sclerotia germinate to form fruiting bodies (basidiomycetes) or mycelium with conidia (in imperfect fungi). Sclerotia sizes can range from a fraction of a millimeter to a few tens of centimeters as, for example '' Laccocephalum mylittae'', which has sclerotia with diameters up to 30 cm and weighing up to 20 kg. Sclerotia resemble
cleistothecia An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mo ...
in both their morphology and the genetic control of their development. This suggests the two structures may be homologous, sclerotia being
vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
cleistothecia that lost the capacity to produce
ascospore An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera ...
s.


History

In the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
''Claviceps purpurea'' sclerotia contaminated rye grain used in bread led to
ergot poisoning Ergotism (pron. ) is the effect of long-term ergot poisoning, traditionally due to the ingestion of the alkaloids produced by the ''Claviceps purpurea'' fungus—from the Latin "club" or clavus "nail" and for "head", i.e. the purple club-head ...
by way of which thousands of people were killed and mutilated. ''Claviceps purpurea'' sclerotia contain
alkaloids Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...
that, when consumed, can cause
ergotism Ergotism (pron. ) is the effect of long-term ergot poisoning, traditionally due to the ingestion of the alkaloids produced by the '' Claviceps purpurea'' fungus—from the Latin "club" or clavus "nail" and for "head", i.e. the purple club-he ...
which is a disease that causes paranoia and hallucinations, twitches, spasms, loss of peripheral sensation,
edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...
and loss of affected tissues.
Louis Rene Tulasne Louis René Étienne Tulasne, a.k.a. Edmond Tulasne (12 September 1815 – 22 December 1885) was a French botanist and mycologist born in Azay-le-Rideau. He originally studied law at Poitiers, but his interest later turned to botany. As a youn ...
discovered the relationship between infected rye plants and ergotism in the 19th century. With this discovery, more efforts were developed to reduce sclerotia from growing on rye and ergotism became rare. However, in 1879–1881 an outbreak developed in Germany, in 1926–1927 Russia was infected, and in 1977–1978 Ethiopia was infected. '' Pleurotus tuber-regium'', which forms edible sclerotia up to 30 cm wide, has a
history History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the invention of writing systems is considered prehistory. "History" is an umbrella term comprising past events as well ...
of economic importance in Africa as food and as a medicinal mushroom.


As part of fungal life cycles

For example, '' Claviceps purpurea'' sclerotia form and begin regrowth in the spring, infecting grass and rye plants by way of releasing their
ascospores An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or ...
from perithecia. ''Claviceps purpurea'' can infect a wide variety of plants by infecting the
ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
. The fungal spores germinate at the anthesis and grow down the
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...
tube without branching any
hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...
outward. When the fungus reaches the bottom of the ovary, it leaves the pollen tube path and enters the vascular tissues where it branches its hypha. Approximately seven days into the infection, the mycelium produces
conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to t ...
. The conidia are then secreted out of the plant in a sugary liquid that insects, attracted by the sugars, transfer to other plants. After two weeks of being infected by the fungus, the plant no longer generates the sugary liquid, and the fungus produces sclerotia. The sclerotium is an overwinter structure, which contains ergot alkaloids. ''Claviceps purpurea''s life cycle is an interesting model for plant pathologists and cell biologists because: * Strict organ specificity (ovaries) * The plant lacks defense reactions * Strict polar, oriented growth in the first infection stage *
Biotrophic Symbiosis (from Ancient Greek, Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different Organism, biological organisms, be it Mutualism (biolog ...
life style


Formation

In fungi, there are three stages in the development of sclerotia: #Initial aggregation of hyphae; #Increase in size due to the growth and branching of hyphae; #Maturation with the formation of an outer coating that isolates the sclerotia from the surrounding environment, with the progressive dehydration of the hyphae and accumulation of reserve substances and pigments.


As food


''Pleurotus tuber-regium''

'' Pleurotus tuber-regium'', which forms edible sclerotia up to 30 cm wide, has a
history History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the invention of writing systems is considered prehistory. "History" is an umbrella term comprising past events as well ...
of economic importance as food in Africa.


Sclerotia as medicine and hallucinogenic drug

Over billions of years of Earth's history, organisms have acquired the ability to produce secondary metabolites, that is chemical compounds that afford protection from
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...
s and
ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiatio ...
damage from the sun. Fungi are no exception, and due to their exposure to a wide variety of environments, they have developed the ability to produce a large number of such chemical compounds that are very valuable in
medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...
.


''Claviceps purpurea''

In early times, ergot alkaloids have been used for medicinal purposes. For example, ergot was used as a form of abortion in Europe, but it led to hyper-contraction. In the 19th century, it was used to aid in the prevention of bleeding after childbirth and treatment for migraines and
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms beco ...
. Acid hydrolysis is used to convert alkaloids, produced by the fungus '' Claviceps purpurea'', into D-lysergic acid which is the starting material for many pharmaceutical and recreational drugs. In 1938 Albert Hofmann synthesized one of the strongest known hallucinogens, lysergic acid diethylamide (LSD), from ergot alkaloid. Despite side effects of the drug such as paranoia, loss of judgment and flashbacks, psychotherapists and psychiatrists used it to treat patients with neuroses, sexual dysfunctions and anxiety. The secret service may have also used it for interrogation purposes. In 1966 the United States government made LSD illegal. Recently, clinics have shown an interest in ergoline to treat patients with autism.


''Ophiocordyceps sinensis''

''Ophiocordyceps sinensis'' (syn. ''Cordyceps sinensis'') is a fungus which infects a caterpillar and uses nutrients out of it to create mycelia and replaces its body with a sclerotium. The fungus then sprouts out of the head of the caterpillar. In Chinese the fungus is known as ''Dōng chóng xià cǎo'' ().


''Inonotus obliquus''

''
Inonotus obliquus ''Inonotus obliquus'', commonly called chaga (a Latinisation of the Russian word ''чага''), is a fungus in the family Hymenochaetaceae. It is parasitic on birch and other trees. The sterile conk is irregularly formed and resembles burnt ...
'' (chaga mushroom) is a sclerotium growing mostly on
birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' cont ...
trees in northern climates. It has been used as a tonic and a remedy for thousands of years in Canada, Russia, Japan, etc. The tree sclerotium develops over the years as the mycelium sucks the energy of the living tree.


''Psilocybe galindoi''

Certain grassland ''
Psilocybe ''Psilocybe'' ( ) is a genus of gilled mushrooms, growing worldwide, in the family Hymenogastraceae. Most or nearly all species contain the psychedelic compounds psilocybin and psilocin. Taxonomy Taxonomic history A 2002 study of the m ...
'' species have sclerotia to protect them from fire and from other disturbances. The sclerotia forming species contain, as many ''Psilocybe'' species do, the organic compounds psilocin and
psilocybin Psilocybin ( , ) is a naturally occurring psychedelic prodrug compound produced by more than 200 species of fungi. The most potent are members of the genus ''Psilocybe'', such as '' P. azurescens'', '' P. semilanceata'', and '' P.&nbs ...
, which are actively being researched to treat
cluster headaches Cluster headache (CH) is a neurological disorder characterized by recurrent severe headaches on one side of the head, typically around the eye(s). There is often accompanying eye watering, nasal congestion, or swelling around the eye on the ...
, depression, and to help the mental health of people with fatal
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
.


''Psilocybe mexicana'' and ''Psilocybe tampanensis''

Sclerotia from ''Psilocybe mexicana'' and ''Psilocybe tampanensis'' also contain the active metabolites psilocin and psilocybin. These sclerotia can be bought at smartshops under different trade names such as "Philosopher's Stone" or "truffles" and have the same hallucinogenic effect as
magic mushrooms Psilocybin mushrooms, commonly known as magic mushrooms, are a polyphyletic informal group of fungi that contain psilocybin which turns into psilocin upon ingestion. Biological genera containing psilocybin mushrooms include ''Psilocybe'', ...
.


''Wolfiporia extensa''

'' Wolfiporia extensa'' is used as a medicinal mushroom in
Chinese medicine Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. It has been described as "fraught with pseudoscience", with the majority of its treatments having no logical mechanism of action ...
. Common names for it include ''hoelen'', poria, ''tuckahoe'', China root, ''fu ling'' (茯苓), ''fu shen'' (or ''fushen'') and ''matsuhodo''.


Some species with sclerotia as agricultural pests

Many methods have been created to reduce the growth of agriculturally pathogenic sclerotia like changes in crop rotation, deeper ploughing and sifting out sclerotia. Fungicides, breeding disease resistance rye and cross breeding natural rye with hybrid rye have reduced ''C. purpurea'' infections. '' Sclerotium cepavorum'' causes white rot in ''
Allium ''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, D ...
'' species, particularly onions, leeks, and garlic. Worldwide, white rot is probably the most serious threat to ''Allium'' crop production of any disease. Other fungi that produce sclerotia are prominent pathogens for
canola Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, ...
crops. These and related fungi are generally controlled through the use of fungicides and
crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...
. File:Sclerotium delphinii on Hosta.jpg, '' Sclerotium delphinii'' sclerotia on infected host File:Athelia rolfsii sclerotia.jpg, ''
Athelia rolfsii ''Athelia rolfsii'' is a corticioid fungus in the family Atheliaceae. It is a facultative plant pathogen and is the causal agent of "southern blight" disease in crops. Taxonomy The species was first described in 1911 by Italian mycologist Pier ...
'' sclerotia on '' Solanum lycopersicum'' (tomato)


Notes


References

{{Authority control Fungal morphology and anatomy Fungal plant pathogens and diseases