Ergot of Small Grains and Grasses

Ergot of Small Grains and Grasses


Ergot has plagued the human race and their crops for centuries. In some cases it has caused significant yield loss but in most instances, toxins produced by the fungus that causes the disease have produced the most problems. The causal organism of the disease is Claviceps purpurea (Fr.:Fr.)Tul. (anamorph Sphacelia segetum Lev.). Many cereals and grasses, both cultivated and wild are hosts of the fungus. The primary cultivated crop host is rye but wheat , barley, oats and triticale are also susceptible. The disease is favored by wet cool weather that aids in spore dissemination and prolongs flowering. The fungus overwinters as sclerotia in the soil surface or mixed with seed. In the later case, fields become contaminated when the sclerotia are sown with the seed. Sclerotia germinate forming a stroma atop a stalk-like structure (stipe). Germination occurs about the same time the crop is flowering. Ascospores are released from the stroma and are windblown or rain splashed to the flower. Infection occurs on the stigma and the fungus grows down the pollen tube into the ovary. Since the fungus specifically in infects exposed flowers, cereal crops with an open or prolonged flowering habit are more susceptible than those that are pollinated in the boot. Honeydew containing conidia is formed on the ovary within 5 days of infection. Conidia serve as secondary inoculum and are spread by direct contact with uninfected florets, insects and splashing rain. As the season progresses, conidia production ceases and a sclerotium begins to form in each infected floret. The sclerotia are 2-20 mm long and blue-black in color. Sclerotia produces on grasses are usually more slender and smaller than those produced on wheat. When the field contains weedy grasses, sclerotia from these hosts may be harvested and contaminate the grain. Alkaloids produced in the sclerotia function as vasoconstrictors in humans and other animals. They can be used for medicinal purposes in low dosages but can cause gangrene (ergotism) and death in high doses. For this reason grain elevators have adopted a zero tolerance for sclerotia in seed lots. In some cases the fungus does not produce sclerotia, leaving infected florets intact but sterile.

Symptoms


The most distinct symptoms of ergot are the presence of sclerotia in the head and honeydew. Early symptoms of sclerotia development may be seen on ovaries upon close examination. Infected ovaries appear convoluted and are covered with a dense layer of conidia. Infected florets may also take on a sooty appearance when saprophytic fungi colonize the honeydew produced by C. purpurea.

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.