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Ergot fungi (Claviceps species) – replacing cereal and grass seed by toxic sclerotia

Ergot fungi (Claviceps species) – replacing cereal and grass seed by toxic sclerotia

Feather Reed Grass
(Calamagrostis arundinacea)
infected with common ergot
(C. purpurea) Photo: Silvio Uhlig

Ergot fungi (Claviceps species) are parasites on more than 600 grass species, including forage grasses and leading cereals worldwide: wheat, rice, barley, sorghum, oats, rye and millet. These fungi may produce a wide range of toxic substances that were responsible for the mass poisonings in the Middle Ages.

Then, at least several 100.000 people died of a disease called “St. Anthony’s fire” when they consumed rye that was infected with purple ergot (Claviceps purpurea). Since the toxins produced by ergot fungi may affect the central nervous system some of the witch trials of the Middle Ages are now assumed to be caused by Claviceps poisoning.

Short overview of the ergot fungi
The genus Claviceps includes much specialised fungi which parasitize only the flowers of specific grasses; no other part of the plant is infected. During infection, the ovary is replaced by a specialized fungal structure called a sphacelium that in time becomes another structure called a sclerotium (the “pseudoseed”). The sclerotium resembles a seedgrain but is a hard, compact mass of fungal tissue with a thin outer layer (rind). Sclerotia of most Claviceps species are one to four times larger than the host seed. Grasses with small seeds, e.g. Agrostis will yield much smaller sclerotia than larger seeded grasses e.g. Lolium.

The disease caused by Claviceps and the sclerotia that develop have the common name ergot. Eventually the supply of susceptible flowers is depleted, or the crop is harvested, and Claviceps species somehow have to survive a considerable period of time in the absence of the host. The sclerotia provide one possible means of surviving this period for Claviceps pathogens (in Northern Europe the winter season). Once favourable environmental conditions reappear at the start of the next crop season, sclerotia may germinate to produce stalked structures that produce spores, which again may infect the flowers of grass plants.

Distribution of important species
Most Claviceps species are restricted to only one or several grass genera. The exception is the purple ergot caused by C. purpurea, which has a host range exceeding 200 species of grasses.

Claviceps purpurea, purple ergot
The best known species of Claviceps is C. purpurea, often referred to as common or purple ergot. Over 200 grass species, almost all genera in the subfamily Pooidea are susceptible. This group includes many of the important cool season grass genera such as Agrostis, Avena, Dactylis, Festuca, Hordeum, Lolium, Poa, Secale, Triticum. However, Sorghum species are not hosts for C. purpurea. C. purpurea is widely distributed and common in temperate regions. C. purpurea is known to occur in Africa, Asia, Australasia and Oceania, Europe, and the Americas.

Claviceps africana, sorghum ergot
Reports of ergot in Africa from as early as 1924, believed to be C. sorghi, were identified as C. africana in 1991. During the 1990’s C. africana spread to sorghum production regions worldwide at a remarkable rate. By 1997, C. africana was recognized in southern Asia, Africa, Australia, and the Americas.

Claviceps paspali, paspalum ergot
This species originates probably from South America, but has now spread to the USA, Australia and New Zealand, Southern Africa and the Mediterranean region. C. paspali is only known to colonize grasses of the genus Paspalum, which are of importance as animal feed.

The poisons produced by ergot fungi
The sclerotia of many Claviceps species contain alkaloids which can cause toxicity problems if consumed by animals or humans. However, some of the alkaloids present in C. purpurea and some other Claviceps species have been long recognized for pharmaceutical uses, including drugs helpful in childbirth, and in treatment of migraine headaches or psychiatric disorders. Alkaloids from C. purpurea are among the most important natural products used by the pharmaceutical industry.

The following classes of alkaloids are known to occur in sclerotia of Claviceps species:

  • Ergot alkaloids
    • Three subclasses: clavines, simple lysergic acid derivatives, ergopeptines
  • Indole diterpenes

Ergot alkaloids: gangrene and LSD
All ergot alkaloids of importance in terms of biologic activity are derived from lysergic acid. These are chemicals that are well-known because of their action on the central nervous (CNS) and cardiovascular (CVS) system. Depending on their chemical structure some affect primarily the CNS while other affect primarily the CVS. Some lysergic acid amides, most notably LSD (lysergic acid diethyl amide), are of hallucinogenic activity. The effect on the CVS is caused by the contraction of smooth muscle (“vasoconstriction”) resulting in reduced blood flow to peripheral tissues. This leads to diminished blood supply, degeneration of the tissues, and in the most extreme cases to gangrene and loss of the afflicted body parts.

Indole diterpenes
This type of compounds may cause nervous ergotism resulting in “staggers”. Later intoxicated animals may experience paralysis of the posterior limbs, followed by drowsiness, and/or convulsions. Extreme cases of this type of ergotism sometimes result in mortality. Horses, sheep and even carnivores can experience this type of ergotism, but rarely cattle.

Research related to the toxins of Claviceps species at the NVI

  • Study the alkaloid composition of C. purpurea sclerotia from Norwegian grasses
  • Study the alkaloid composition of C. paspali and C. cynodontis of New Zealand and South African origin
  • Investigate the content of sorghum-based fermented drinks with C. africana-related alkaloids from Lesotho (initiated by the Blue Cross)

 

Contact persons
Silvio Uhlig, senior scientist, Section for Chemistry
Telephone: 23 21 62 64
E-mail: silvio.uhlig@vetinst.no

Christopher O. Miles, senior scientist, Section for Chemistry
Telephone: 23 21 62 32
E-mail: chris.miles@vetinst.no

Trude Vrålstad, seniorforsker, Section of mycology
Telefon: 23 21 62 47
E-post: trude.vralstad@vetinst.no