The life cycle of ergot and its impact on cereals and grasses

Although the disease has relatively little impact on cereal yields, ergots are associated with large amounts of toxic alkaloids (mycotoxins). Management interventions can be grouped by the impact on the pathogen’s life cycle.

The ergot pathogen (Claviceps purpurea) grows in and replaces grain with its own fungal tissues, which eventually form a hard, purple-black sclerotium (with a white interior) known as an ergot. They can be up to 2 cm long and are often easy to spot in infected crops and grain.

Cereal crops affected (from the most to the least susceptible):

• Rye
• Triticale
• Wheat
• Barley
• Oats (infection of oats is rare)

Ergot also affects a wide range of grasses, including black-grass.

1. Over the winter, ergots are dormant in the soil or on crop debris (ergots may also be in drilled seed).
2. In the spring and summer (after a period of vernalisation), ergot near the soil surface (<5 cm deep) germinate and produce mushroom-shaped, spore-bearing structures (called stroma).
3. The stroma heads feature asci-containing perithecia, which contain (sexual) ascospores.
4. The structure ejects the ascospores, which are carried on the wind.
5. When these primary spores land on open flowers of cereals and grasses they germinate and penetrate the stigma hairs.
6. Fungal hyphae grow down into the ovary.
7. In the ovary, the fungus produces a soft, white hyphal mass and secondary (asexual) spores (conidia) encased in a sweet-smelling, sticky secretion – commonly referred to as honeydew.
8. Honeydew attracts insects that carry conidia to other open flowers, where further infection can occur (rain-splash and physical contact can also spread spores).
9. Infected seed is replaced by a relatively large, protruding ergot (the process takes about two weeks), which may fall to the ground (and become dormant over the winter) or be retained in the ear and harvested with healthy grain.

Notes:

• Ergot spores do not travel far from the source (a study in France saw a 50% reduction in disease level within 5 m of the primary source of ergot and a 95% decrease in ascospores spread within a 20 m radius of the source)
• Cool and wet conditions promote spore production and prolong the flowering period (making infection more likely)
• Late-tillering crops and crops with secondary tillers are more susceptible
• Honeydew can promote the development of saprophytic moulds
• Typically, ergots remain viable in the soil for one to three years
• Ergots can survive for over a year in stored grain

Honeydew symptoms

Ergot in a developing ear

Ergot in a grass weed

Ergot in a sample of grain