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Ergot:essential data

Disease Name, Other Names, Crops Affected Causative Agent, Synonyms,
Description of the Agent Symptoms, Prevention and Treatment
Other Comments
Disease name Ergot
Other Names Ergot of Rye
Causative Agent

Claviceps purpurea
Synonyms
  • Cordyceps purpurea
  • Sclerotium clavus
  • Sphacelia segetum
  • Sphaeria purpurea
Crops Affected Cereals and grasses. The most significant is rye.
Description of the Agent Claviceps purpurea is an ascomycete or sac fungus, so called because the spores arising from a sexual cross (ascospores) mature in structures called asci in a sac-like structure called a perithecium. Like many other ascomycetes, C. purpurea spreads using asexual spores called conidia. It overwinters in the soil using a refractory structure called a sclerotium. Germination begins when conditions are relatively warm (>10°C) and humid. The sclerotium germinates after wet weather to produce a number of ascospore-bearing structures called stroma. The dispersed ascospores infect the developing ear of the plant. After germination, the fungus begins to secrete a sticky, sweet substance called honeydew that contains conidia. Insects are attracted by the honeydew and spread the conidia to other plants.
Symptoms After the spores infect the plant, the appearance of honeydew is the first obvious symptom. This is followed by the development of sclerotia. They replace individual kernels with the obvious hard, dark structure that can be several millimeters to centimeters long. The replacement of the kernels results in a loss of yield, of the order of 5-10% loss, and also affects the economic value. Crops with more than a very low level of sclerotia will be either unmarketable or have to be cleaned at a significant cost.
Prevention and Treatment The primary response to infection is cultural rather than chemical. There are no fungicides registered for use against the fungus in the US and there are also no ergot-resistant varieties of cereal crops.. The sclerotium cannot survive for more than one winter in the soil, so planting non-susceptible crops in infected fields for two years will clear them out and when replanted, ergot-free seed should be used. The areas surrounding infected fields should also be cleared of susceptible plants. In severe cases, deep ploughing to bury sclerotia is also helpful.
Other Comments

The primary concern with ergot is that it produces a number of alkaloids, known as ergot alkaloids, that are highly toxic to humans and to livestock. Precise symptoms will depend upon the ratios of the various alkaloids produced by the infecting strain.

The toxicity of ergot was known to Assyrians and the earliest descriptions of infected cereals date from these times. Medical texts on cuneiform tablet from about 600 BC describe a noxious pustule in the ears of grain. During the period of the Roman Empire, effective grain husbandry limited outbreaks, but a series of severe outbreaks leading to large numbers of deaths occurred sporadically in the period between the fall of the Roman empire and the Rennaissance, although outbreaks continue to this day. It is thought that the strange behaviors of women in Salem, Massachussetts, that led to the Salem witch trials of the 1692, may have resulted to exposure to hallucinogenic ergot alkaloids.

Ergotism became known as St. Anthony's fire because pilgrimages to the shrine of St. Anthony lead to the disease being cured. The shrine is in the Swiss mountains, where conditions do not favor the growth of the fungus. People travelling through the area would be eating ergot-free bread and so would recover. However, at low doses it was found to be therapeutic and sclerotia were often taken in small quantities to aid childbirth.

The disease was first fully described in 1676 and was finally identified as a fungus in 1815.

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