Fig. 24-3. Fine fescue (Festuca spp.) with sclerotia of Claviceps purpurea.
Ergot is caused by the flower-infecting fungus Claviceps purpurea. The disease is characterized by elongated, hard, black sclerotia that extend beyond the lemma and palea in infected seeds (Fig. 24-3). Each infected seed is replaced by a single sclerotium. The sclerotium is the overwintering structure for C. purpurea. In the spring, about the time of flowering in the grasses, spherical, stalked fruiting bodies emerge from the sclerotia. Wet, rainy conditions favor sclerotial germination and release of ascospores. The ovary is the only plant part infected.
Within a week of infection, conidia are produced in large numbers. Conidia, combined with plant sap, can ooze from infected flowers in what is commonly referred to as the honeydew stage. The honeydew stage is followed by development and maturation of sclerotia. Maturity of the sclerotia coincides with maturation of healthy seed. The host range for C. purpurea includes 300 to 400 grass species, including the cereal grains and grasses for forage and turf (see Chapter 26). Normally, ergot is not a serious problem in tall fescue seed production. The literature on ergot is extensive, and several comprehensive reviews are available (Barger, 1931; Bove, 1970; Kren and Cvak, 1999).