Ergot of cereals: a literature review and survey of incidence in traded grain

Although the pathogen Claviceps purpurea seldom causes serious losses of yield, the alkaloids which its sclerotia ('ergots') contain are so toxic both to humans and to their animals that ergot contamination of grain lots greatly reduced their value. Postal surveys of grain merchants revealed that contamination of grain could not only reduce the price paid to the farmer but might lead to the complete rejection of consignments. The surveys showed the incidence of contamination to be particularly high in spring wheat and rye in the East Midlands and East Anglia.

Mature ergots may fall to the ground or be harvested with the grain. In the latter case, they may serve to introduce the pathogen into other fields if the contaminated grain is used for seed. In either case, they lie dormant over winter, germinating (after a period of chilling) in the spring. The fruiting bodies which develop from the germinating ergots produce 'ascospores' which are able to infect the cereals or grasses at the time of anthesis. Spores of another kind ('conidia') are produced on the first infected inflorescences and these, transmitted by insects or rainsplash, serve further to spread the disease within the crop. Ultimately, infected florets produce more sclerotia in place of healthy grain. Sclerotial germination, spore production and infection are all very dependent on weather conditions. Levels of the disease are likely to be highest in cool, wet seasons.

Cross pollinated cereal species, in which the glumes gape for a long period during anthesis, are most susceptible to the disease. Thus, rye, triticale and durum wheat are more susceptible to infection than are bread and feed wheats and barley. In closed flowering species, any factor which reduces pollination, and/or causes the glumes to gape longer, increases the risk of infection.

Early flowering grasses can act as alternative hosts for the fungus allowing it to build up within or around a field before the cereal crop flowers.

Strains of the pathogen especially well adapted to particular species or groups of species are known to exist, but the strains appear not to be very distinctly differentiated and to vary from area to area. In England, a strain which attacks blackgrass will spread very readily to wheat, and ergot is most frequently found on wheat in fields infected with this weed.

Animals and poultry fed on a contaminated grain (or grazing contaminated pastures) can suffer severely from the toxic effects of the ergot alkaloids. Symptoms vary with dose and with the species affected but include gangrene (leading to loss of extremities), abortion and, in extreme cases, death.

Ergotism in humans is now rare but in past centuries has sometimes reached epidemic proportions in rye growing areas. Gangrenous and convulsive forms of the disease have been recorded, the latter apparently having been more prevalent where the diet of sufferers was deficient in vitamin A.

Despite their toxicity, ergot alkaloids have found a number of uses in medicine, more particularly in obstetrics and in the treatment of migraine. Cultivation of ergot for pharmaceutical use has been practised in many countries since the Second World War.

Strategies advocated for the control of ergot include the use of uncontaminated seed, rotation of crops, deep ploughing to bury the sclerotia and the control of weed grasses. The use of fungicides sprayed onto the ground to prevent infection, has been tried but (at present) finds no place in commercial practice. The use of biological control agents has also been investigated. Certain fungicides applied as seed treatments will suppress the germination of sclerotia occurring as contaminants in the seed lot.

There is a need for further research on the role of weed grasses in ergot epidemiology, and on the effects of the new generation of fungicides on the infection process. Spray timing trials using these materials on carefully monitored plots artificially contaminated with sclerotia could yield valuable information on both epidemiology and control.