Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Claviceps gigantea
(horse's tooth)



Claviceps gigantea (horse's tooth)


  • Last modified
  • 20 November 2019
  • Datasheet Type(s)
  • Documented Species
  • Pest
  • Preferred Scientific Name
  • Claviceps gigantea
  • Preferred Common Name
  • horse's tooth
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Fungi
  •     Phylum: Ascomycota
  •       Subphylum: Pezizomycotina
  •         Class: Sordariomycetes
  • Summary of Invasiveness
  • This pathogen only occurs in certain high humid valleys of Mexico and is apparently not adapted to surrounding drier areas where maize [Zea mays] is certainly grown. Its host range and environ...

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Ear rot.
TitleSymptoms on ear
CaptionEar rot.
Ear rot.
Symptoms on earEar rot.©CIMMYT
Kernel rot and apothecia.
TitleSymptoms on kernel
CaptionKernel rot and apothecia.
Kernel rot and apothecia.
Symptoms on kernelKernel rot and apothecia.©CIMMYT


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Preferred Scientific Name

  • Claviceps gigantea SF Fuentes, Isla, Ullstrup & AE Rodr 1964 (teleomorph)

Preferred Common Name

  • horse's tooth

Other Scientific Names

  • Sphacelia sp. SF Fuentes, Isla, Ullstrup & AE Rodr 1964 (anamorph)

International Common Names

  • English: ergot of maize; maize ergot
  • Spanish: cornezuelo del maíz; diente de caballo
  • French: ergot du maïs

Local Common Names

  • Germany: Mutterkorn: Mais

EPPO code

  • CLAVGI (Claviceps gigantea)

Summary of Invasiveness

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This pathogen only occurs in certain high humid valleys of Mexico and is apparently not adapted to surrounding drier areas where maize [Zea mays] is certainly grown. Its host range and environmental tolerances have not been determined, so that the risk that would result from an introduction to distant regions cannot be known. Human mistakes, such as the transport of contaminated maize seed, would be the most likely means by which it could bypass ecological and geographic barriers to reach other humid parts of the world, where it might be a problem on maize. In Mexico, it can reduce yield of a maize ear by 50% (Fucikovsky and Moreno, 1971), so preventing its spread is a serious consideration.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Fungi
  •         Phylum: Ascomycota
  •             Subphylum: Pezizomycotina
  •                 Class: Sordariomycetes
  •                     Subclass: Hypocreomycetidae
  •                         Order: Hypocreales
  •                             Family: Clavicipitaceae
  •                                 Genus: Claviceps
  •                                     Species: Claviceps gigantea

Notes on Taxonomy and Nomenclature

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Fuentes et al. (1964) identified C. gigantea as the cause of horse's tooth of maize [Zea mays]. They pointed out that a maize disease with ergot symptoms had been mentioned in 1829 by Roullin and that maize had been listed as a host of Claviceps purpurea by Zopf in 1890. However, no evidence could be found in the early literature to prove this relationship.

Fuentes et al. (1964) clearly described both the symptoms of horse's tooth and the morphology of the causal organism, C. gigantea. They also demonstrated that C. gigantea, but not C. purpurea, is pathogenic to maize.


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Sclerotia initially white to cream, 5-8 x 2-5 cm, soft, sticky and hollow, later becoming hard and horny, white to brown, with pink to lavender centres, often comma-shaped, resembling a horse's tooth.

Stromata long-stalked, stalks 26-58 x 2-3.5 mm diameter, pink to reddish-brown, heads capitate or globose, 32–55 mm diameter, pink, sticky.

Perithecia flask-shaped, 338-444 x 152-164 µm, in large numbers within stroma, ostioles visible as darker spots on the stroma surface.

Asci cylindrical, 187-201 x 4.5-4.7 µm, eight-spored.

Ascospores filiform, hyaline, aseptate, 176-186 x 1.5 µm.  

Conidiogenous cells in palisades on sclerotium surface and lining walls of cavities, proliferating percurrently, 8-17 x 2-3 µm.

Macroconidia ellipsoidal, 8.3-27 x 4.2-5.8 µm. Microconidia ovoid, 4.2-6.7 x 2.5-3.3 µm. Both hyaline, aseptate (Fuentes et al., 1964).

Pazoutova et al. (2004) reported that the macroconidia can produce secondary conidia in vitro. These conidia are hyaline, ovoid to pyriform, approximately the same size as the macroconidia, and produced holoblastically. Also, unlike the macroconidia of some other Claviceps species, those of C.gigantea did not germinate to develop vegetative mycelium in culture.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 12 May 2022
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

North America

MexicoPresent, LocalizedNativeStates of Mexico, Michoacan, Veracruz

Risk of Introduction

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C. gigantea is of low economic importance, has moderate seedborne incidence and is seed transmitted. Although, where it occurs, the disease can be quite severe, it has such a narrow ecological niche that it poses a very low threat to maize [Zea mays]-growing regions throughout the world.

Hosts/Species Affected

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Fuentes et al. (1964) demonstrated that C. gigantea is pathogenic to maize [Zea mays] and that C. purpurea is not pathogenic to maize.

Host Plants and Other Plants Affected

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Plant nameFamilyContextReferences
Zea mays (maize)PoaceaeMain

Growth Stages

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Fruiting stage


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Sclerotia that replace the kernels are initially white to cream, 5-8 x 2-5 cm, soft, sticky and hollow. Mature sclerotia are comma-shaped, resembling a horse's tooth, and white to greyish-brown. Those beneath the husks are lighter in colour. Each ear may contain one to several sclerotia. The 'honeydew' of the sclerotia is filled with small, hyaline ovoid to ellipsoidal spores (Fuentes et al., 1964).

List of Symptoms/Signs

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SignLife StagesType
Inflorescence / black fungal spores
Inflorescence / honeydew or sooty mould

Biology and Ecology

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The disease occurs only in high, humid mountain valleys in central Mexico. Disease development is favoured by mean annual temperatures of 13-15°C and high rainfall (1,000 mm per year) (Fucikovsky and Moreno, 1971). Ullstrup (1973) stated that it was a disease with a restricted ecological niche.
The fungus overwinters as sclerotia on the ground or mixed with seed. In the spring, sclerotia germinate to produce stalked stromata with heads containing many embedded perithecia. Ascospores serve as the primary inoculum; they are forcibly ejected from asci and carried by the wind to the floral parts of susceptible maize [Zea mays] plants. Sphacelial tissue in cavities, in and on the sclerotia, produce macroconidia and microconidia in a sticky matrix ('honeydew') (White, 1999).
Conidia, transported to other flowers and plants, cause secondary infections. Insects, feeding on honeydew, may play a role in transporting conidia according to White (1999), but Pazoutova (2003) notes that enclosure of the Sphacelia inside the husks of the maize ear makes the honeydew unavailable to insects. Nevertheless, no genetic differences between populations in the isolated mountain valleys were detected by AFLP and RAPD techniques (Pazoutova, 2003). Mixture of genetic material as a result of spore distribution must be occurring by some means. Fuentes et al. (1964) imply that not all sclerotia are covered by the husks. Activities of insects in and around the infected ears need to be observed in the field.
Moreno and Fucikovsky (1972) described the pattern of infection on maize ears with sclerotia developing freely at the top of ears. Each ear may contain one to several sclerotia. On the middle of the ear, several sclerotia together force open bracts, while at the bottom of the ear, sclerotia are flattened over surrounding grains on which exudates are released. These grains turn brown.


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Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Means of Movement and Dispersal

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Local dispersal is natural, by means of airborne ascospores, and possibly by means of insect-borne conidia (White, 1999), or accidental, by transportation of sclerotia in harvested ears or in soil.

Seedborne Aspects

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Many seeds on an ear can be replaced by sclerotia (Fuentes et al., 1964).

Effect on Seed Quality

Germination can be reduced by 50% in seeds from ears bearing only one sclerotium (Fucikovsky and Moreno, 1971). Germination is affected more by sclerotia distributed over the cob than by localized sclerotia (Moreno and Fucikovsky, 1972).

Pathogen Transmission

Sclerotia that might be planted with seed could be a source of inoculum (Fuentes et al., 1964).

Seed Health Tests


Seedlots can be examined for comma-shaped sclerotia.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Host and vector organismsConidia on insects Yes White (1999)
Plants or parts of plantsSclerotia Yes Richardson (1990)
WindAscospores Yes Fuentes et al. (1964)

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Flowers/Inflorescences/Cones/Calyx fungi/hyphae; fungi/sclerotia; fungi/spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
True seeds (inc. grain) fungi/sclerotia Yes Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Fruits (inc. pods)
Growing medium accompanying plants
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches

Impact Summary

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Economic/livelihood Negative


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The disease is confined to high, humid mountain valleys in central Mexico (Fucikovsky and Moreno, 1971; Ullstrup, 1973). It is endemic in these areas and can infect over 50% of maize [Zea mays] ears (Fucikovsky and Moreno, 1971). A single sclerotium in a maize ear can cause a 50% reduction in seed germination (Fucikovsky and Moreno, 1971).

Alkaloids of the dihydroergoline type are present in sclerotia, but their toxicity to humans and animals is not known (Pazoutova, 2003).

Risk and Impact Factors

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  • Abundant in its native range
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
Impact outcomes
  • Host damage
  • Negatively impacts agriculture
Impact mechanisms
  • Pathogenic


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Seed can be examined for sclerotia. C.gigantea can be isolated by surface-sterilizing mature sclerotia and plating fragments of the horny interior on glucose-yeast agar at 24°C to produce slow-growing colonies (Fuentes et al., 1964). Pazoutova et al. (2004) were able to obtain vegetative growth from the lavender tissue of young sclerotia, but not from conidia. Sequences determined for several DNA regions have been deposited in the GenBank database (Pazoutova et al., 2003; Tooley et al., 2006).

Detection and Inspection

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Maize [Zea mays] ears can be examined for comma-shaped sclerotia, resembling a horse's tooth.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

No specific field control methods have been developed. Sclerotia can be removed from seed before planting (Richardson, 1990).

Gaps in Knowledge/Research Needs

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The potential host range and the means of dispersal of conidia outside the ear should be determined, because these are avenues by which the pathogen could be spread naturally beyond its current limited distribution.


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Alvarez MG, 1976. Primer catalogo de enfermedades de plantas Mexicanas. Fitofilo, 71:1-169.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization.

Fucikovsky L; Moreno M, 1971. Distribution of Claviceps gigantea and its percent attack on two lines of corn in the state of Mexico, Mexico. Plant Disease Reporter, 55:231-233.

Fuentes SF; de la Isla ML; Ullstrup AJ; Rodriguez AE, 1964. Claviceps gigantea, a new pathogen of maize in Mexico. Phytopathology, 54:379-381.

Moreno M; Fucikovsky L, 1972. Effect of position and number of sclerotia of Claviceps gigantea on maize germination. Fitopatologia, 5:7-9.

Pazoutova S, 2003. The evolutionary strategy of Claviceps. In: Clavicipitalean Fungi: evolutionary biology, chemistry, biocontrol and cultural impact [ed. by White Jr JF, Bacon CW, Hywel Jones NL, Spatafora JW] New York, USA: Marcel Dekker Inc, 329-354. [Mycology Series No.19.]

Pazoutová S; Kolarík M; Kolínská R, 2004. Pleomorphic conidiation in Claviceps. Mycological Research, 108(2):126-135.

Richardson MJ, 1990. An annotated list of seed-borne diseases. Zurich, Switzerland: The International Seed-Testing Association.

Shurtleff MC, 1980. Compendium of Corn Diseases. St Paul, Minnesota, USA: APS Press, 37.

Tooley PW; Ranajit Bandyopadhyay; Carras MM; Pazoutová S, 2006. Analysis of Claviceps africana and C. sorghi from India using AFLPs, EF-1alpha gene intron 4, and beta-tubulin gene intron 3. Mycological Research, 110(4):441-451.

Ullstrup AJ, 1973. Maize ergot: a disease with a restricted ecological niche. PANS 19:389-391.

White DG, 1999. Ergot. In: Compendium of Corn Diseases. Third edition [ed. by White, D. G.]. St Paul, Minnesota, USA: American Phytopathological Society, 32.


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Mexico: International Maize and Wheat Improvement Center (CIMMYT), Lisboa 27, Apdo, Postal 6-641, 06600,


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10/09/09 Updated by:

Systematic Mycology & Microbiology Laboratory, USDA-ARS, 10300 Baltimore Ave., Beltsville, MD 20705, USA

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