Fusarium Ear Blight Fungus Identified
1. Re-emergence of a destructive cereal disease poses a threat to production of wheat in the UK, according to a recent report received from Rothamsted Research, which is based in Hertfordshire and is one of the biggest agricultural research institutes in the UK. The Applied Crop Science department is based at Broom's Barn, Higham, Bury St Edmunds. Rothamsted Research is an institute of the Biotechnology and Biology Sciences Research Council (BBSRC).
2. Fusarium Ear Blight is a destructive fungal disease in cereals, including wheat, that has the potential to devastate a farmer's crop just weeks before harvest (in other words, about now in the UK's main cereal-growing areas.) Over the last 10 years, on average 38% of wheat crops in the UK had the disease. Scientists at Rothamsted Research have discovered substantial symptom-less infection in wheat ears, which means that, although the plant appears healthy, the fungal infection could already be beyond the control of the farmer. Hence, scientists are advising farmers to use fungicides as a preventive measure rather than a curative approach. It has therefore particular significance for organic farmers and the crops of cereals they are growing to produce feeds and foods that meet their standards and justify stipulations required for inclusion in the Campaign for Real Bread (CAMREB).
3. It is believed that the re-emergence of FEB is driven by changes to our climate and agronomic practices. For example, a greater likelihood of thunderstorms during crop flowering increases the level of infection, using reduced or minimal tillage leads to infected crop residues remaining on the soil surface and causes greater spore production, while growing maize, another susceptible cereal species, in the wheat rotation can increase disease levels. Besides dramatically reducing a farmer yields, the harvested grains are also contaminated with a fungal toxin (mycotoxin), making them unsuitable and unsafe for human consumption, animal feed or malting purposes. Farmers in the UK pay the mill where their grain is processed, to test for the presence of the mycotoxin and under EU safety guidelines about one infected ear per sq m. would be sufficient for their harvest to be rejected. In 2008 11.5% of the wheat crop was found to be over the EU legal limit of contamination by the fusarium mycotoxin called deoxynivalenol (DON) and was rejected from use in the food chain and downgraded for use as an animal feed or for various industrial purposes. Similar problems beset the production of beers. In history the ergot in rye has been a notable example of a mycotoxin persisting in bread and very large outbreaks of mycotoxinosis have broken out in intensively-run poultry enterprises. Aflatoxins are notorious for these events too.
4. Attempts made to control the disease (FEB) by traditional methods such as plant breeding and treatments with fungiade have not been fully effective and may be costly. A definitive infection model of how the fungal pathogen spreads throughout the wheat ear has been developed at Rothamsted Research and described in the journal Fungal Biology. It reveals that these control strategies have proven unsuccessful so far. Neil Brown, who did this research as part of his BBSRC-Syngenta PhD project says: "When symptoms are showing on a couple of spikelets up to one third of the ear is already fully infected."
5. Assessing the amount of infection in the harvest prior to sending grain to the mill could save the farmer time and money. At present assessments are made by scoring visible symptoms of disease. The infection model from Rothamsted demonstrates that the amounts of visible symptoms represent only a small proportion of the total infected area in each ear; consequently, this approach could drastically underestimate disease levels and possible mycotoxin contamination. "By the time you spray when you see symptoms it is too late," says Professor Hammond-Kosack: "it needs to be a preventative spray as the ear is emerging out of the flag leaf - maybe a week to 10 days earlier than most growers spray."
6. This research also has implications for commercial wheat breeding programs, which currently rely on scoring visible disease symptoms and determination of the mycotoxin levels in the final grain. Professor Hammond-Kosack says: "The scoring of visible symptoms on ears should probably be phased out and efforts re-focused on accurately determining the levels of mycotoxin contamination in whole ears and the harvested grain. This would ensure that germ plasm is identified that consistently lowers FEB infections and results in low mycotoxin levels." Future research will investigate the possibility for the delivery of plant-derived antifungal compounds designed to constrain the spread of infection or to inhibit production of the fungal toxin. Research continues at Rothamsted into how this pathogen causes disease, the identification of fungicide targets, and novel control strategies. VEGA, in its role in its Real Bread Campaign, comments on the incidence of such troubles in the final, harvesting, drying and storage of the crop and potential contamination of products for consumption by humans and other livestock intended as sources of food.