Ergot

Pathogen

Claviceps purpurea

Hosts

The disease affects wheat, barley, oats, rye and triticale, and a wide range of grasses, particularly black-grass (Alopercurus myosuroides).

Symptoms

The causal fungus only attacks the ear at flowering, replacing the grain in a few spikelets by a hard, purple-black sclerotium, known as an ergot. Such ergots can be very large, up to 2 cm in length, and are very obvious in the standing crop and in contaminated grain samples.

Life Cycle

Ergot-life-cycle.jpg

Ergot is not truly a seed-borne disease as it is not carried on or in seed. However, it can be spread by ergots in contaminated seed. It is also one of only two diseases which are included in the UK Seed Certification Scheme for Cereals (the other being loose smut).

At or near to harvest, ergots fall to the ground where they remain until the following summer, when they germinate to produce club-shaped spore bearing structures (stroma). These spores are spread by the wind to nearby open flowers of grasses and cereals. The spores germinate in the flower, infecting the ovaries.  This infection leads to the production of secondary spores (conidia) encased in a sticky secretion commonly referred to as honeydew. This attracts insects which carry the spores to other flowers where further infection can occur.

There are a number of strains of the fungus, some of which can infect grasses and cereals, others which are restricted to certain hosts. Wheat and other cereals are less commonly affected than rye although occasionally more open-flowered wheat varieties can be badly affected. The disease is favoured by cool, wet conditions during flowering which facilitate spore production and prolong the flowering period - making infection more likely.

Importance

The disease has very little direct effect on yield but the ergots contain large amounts of toxic alkaloids. Consequently, if grain contaminated with ergots is fed to stock or used to make flour then there are real risks to animal and human health. As a result, contaminated grain may be rejected.