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Claviceps purpurea
Claviceps purpurea
Scientific classification
Kingdom: Fungi
Division: Ascomycota
Class: Euascomycetes
Order: Hypocreales
Family: Clavicipitaceae
Genus: Claviceps
About 50, including:
Claviceps africanum
Claviceps fusiformis
Claviceps paspali
Claviceps purpurea

Ergot is the common name of a fungus in the genus Claviceps. The fungus is parasitic on certain grains and grasses. The form the fungus takes to over-winter is called a sclerotium, and this small structure is what is usually referred to as 'ergot', although referring to the members of the Claviceps genus as 'ergot' is also correct. There are about 50 known species of Claviceps, most of them in the tropical regions. Economically important species are Claviceps purpurea (parasitic on grasses and cereals), C. fusiformis (on pearl millet, buffel grass), C. paspali (on dallis grass), and C. africana[1](on sorghum). C. purpurea can affect a number of cereals including rye (its most common host), triticale, wheat and barley. It affects oats only rarely.

There are three races or varieties of C. purpurea, differing in their host specifity [2]: G1 - land grasses of open meadows and fields; G2 - grasses from moist, forest and mountain habitats; G3 (C. purpurea var. spartinae) - salt marsh grasses (Spartina, Distichlis).


Life cycle of the fungus

An ergot kernel called a sclerotium develops when a floret of flowering grass or cereal is infected by a spore of Claviceps fungus. The infection process mimicks a pollen grain growing into an ovary during fertilization. The fungus then destroys the plant ovary and attaches itself to a vascular bundle originally intended for seed nutrition. The first stage of ergot infection manifests itself as a white soft tissue (known as sphacelia) producing sugary honeydew, which often drops out of the grass florets. This honeydew contains millions of asexual spores (conidia) which are dispersed to other florets by insects. Later, the sphacelia convert into a hard dry sclerotium inside the husk of the floret. At this stage, alkaloids and lipids accumulate in the sclerotium.

Claviceps species from tropic and subtropic regions produce macro- and microconidia in their honeydew. Macroconidia differ in shape and size between the species, whereas microconidia are rather uniform, oval to globose (5x3um). Macroconidia are able to produce secondary conidia. A germ tube emerges from a macroconidium through the surface of a honeydew drop and a secondary conidium of the oval to pearlike shape is formed to which the contents of the original macroconidium migrates. Secondary conidia form white frost-like surface on honeydew drops and are spread by wind. No such process occurs in Claviceps purpurea, Claviceps grohii, Claviceps nigricans and Claviceps zizaniae, all from North temperate regions.

When a mature sclerotium drops to the ground, the fungus remains dormant until proper conditions trigger its fruiting phase (onset of spring, rain period, etc.). It germinates, forming one or several fruiting bodies with head and stipe, variously colored (resembling a tiny mushroom). In the head, threadlike sexual spores are formed, which are ejected simultaneously, when suitable grass hosts are flowering. Ergot infection causes a reduction in the yield and quality of grain and hay produced, and if infected grain or hay is fed to livestock it may cause a disease called ergotism.

Black and protruding sclerotia of C. purpurea are well known. However, many tropical ergots have brown or greyish sclerotia, mimicking the shape of the host seed. For this reason, the infection is often overlooked.

Effects on humans and animals

Ergot contains alkaloids of the ergoline group, which have a wide range of activities including effects on circulation and neurotransmission. Ergotism is the name for the collection of symptoms a human or animal has when it has ingested (too much of) this fungus. Ergotism went also under the name "St. Anthony's fire" hinting at burning sensations in the limbs[3]. Another effect of ergot alkaloids is vasoconstriction, therefore ergotism may lead to gangrene and loss of the limbs due to limited blood circulation. This may also cause insanity, convulsions, or death, due to limited circulation to the brain. Other symptoms include strong uterine contractions, nausea, seizures, and unconsciousness. Monks of the order of St. Anthony the Great specialized in treating ergotism victims with balms containing tranquilizing and blood circulation-stimulating plants; they were also skilled in amputations. Entire villages have been known to suffer ergotism after the village bakery used infected grain.

In addition to ergot alkaloids, Claviceps paspali also produces tremorgens (paspalitrem) causing "paspalum staggers" in cattle.

Historically, controlled doses of ergot were used to induce abortions and to stop maternal bleeding after childbirth, but simple ergot extract is no longer used as a pharmaceutical.

Among those who studied ergot and its derivatives was Albert Hofmann, whose experiments led to the discovery of LSD, a powerfully hallucinogenic ergot derivative that affects the serotonin system. Contrary to some rumors, ergot contains no LSD, but there are links between the two substances:

  • LSD was first synthesised during research on the active ingredients of ergot.
  • Lysergic acid, a raw material used in the synthesis of LSD, was and is still prepared from ergot.


Ergot on wheat spikes
Ergot on wheat spikes

The disease cycle of the ergot fungus was first described in the 1800s, but the connection with ergot and epidemics among people and animals was known several hundred years before that.

Human poisoning due to the consumption of rye bread made from ergot-infected grain was common in Europe in the Middle Ages. The phenomenon known as Dancing mania has been blamed on accidental consumption of the fungus.

It has also been posited though speculatively that the Salem Witch Trials were initiated by young women who had consumed ergot-tainted rye. The Great Fear in France during the Revolution has also been linked by some historians to the influence of ergot. Most famously, ergot intoxicated a whole French village in 1951, at Pont-Saint-Esprit.

Kykeon, the beverage consumed by participants in the ancient Greek mystery of Eleusinian Mysteries, might have been based on hallucinogens from ergot.

Nowadays, rye grain is infected repeatedly to produce ergot.

External links

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