Infection of ears of cereals, especially wheat, by Fusarium fungi can lead to contamination of grain, and hence grain products, with mycotoxins that are a hazard to the health of human and livestock consumers. The principle mycotoxins include trichothecene compounds such as deoxynivalenol (DON) and nivalenol (NIV). Fusarium ear blight, the visible symptom of ear infection, and consequent contamination of grain with trichothecene mycotoxins increased to devastating proportions in the 1990s in some parts of the world, particularly North America and Central Europe. It has not yet achieved such severity in the UK but it is cause for concern because of increasing levels of disease and mycotoxins and impending legal limits on these mycotoxins in the EU. Information from Defra-funded surveys, obtained by unbiased sampling of representative crops, has confirmed that F. graminearum, the fungus that has caused such problems elsewhere, has recently become the most frequent trichothecene-producing ear blight pathogen on wheat in England and Wales. Its continued increase can be expected because of farming practices, such as minimum tillage, and climate change towards warmer seasons. Because of this, and the need for risk assessment based partly on up-to-date regional information, continued monitoring is required. Crop surveys (Defra- and FSA/HGCA-funded) are providing information that underpins our experimental data on factors that can limit ear blight and mycotoxins, such as dry weather in June (during the flowering period, when the ear is susceptible) and ploughing-in infested crop debris. We now have evidence from experiments for the relative importance of factors reported to have the main influences on ear blight development, particularly minimum tillage and maize in rotations and we have also established that the presence of adequate inoculum on infested residues of previous crops is an overriding factor.
Understanding the epidemiology of fusarium ear blight, necessary for its effective control, has depended mainly on published research from North America or Central Europe, which has almost always concerned F. graminearum, the fungus responsible for the problems in those places, rather than F. culmorum, formerly the more abundant of these two toxigenic species here and which is still widespread here. This information is, therefore, not necessarily appropriate for developing disease management strategies in the UK, where weather patterns and the prevalent pathogens are different. Our current Defra-funded research (project AR0515) is establishing epidemiological differences between F. graminearum and F. culmorum. Additional epidemiological information is still required. In particular, whilst we have evidence that rainfall, known to be necessary for ear infection via the anthers, helps dispersal from the ground to the ears, the amount and precise timing of this rainfall is unclear, even though leaf infection does not appear to be an important intermediate stage. Dispersal via the leaf layers may, however, result from transient occupation on leaf surfaces by water droplets containing spore inoculum. Also, inoculum is potentially a mixture of the two main trichothecene-producing species and their chemotypes (which produce different trichothecene mycotoxins), the proportions of which are likely to continue changing, and which, according to preliminary results, interact differently with different cereal hosts and with other pathogens such as Microdochium spp.; the epidemiological implications of this are not known. The complexity of the situation is further increased by the presence of other mycotoxin-producing species; the status and consequences of mixed infections and changes in the balance of these are also uncertain.
New research is proposed that employs the combined expertise and techniques available at Rothamsted Research (RRes) and John Innes Centre (JIC). Further essential epidemiological information will be obtained by field experimentation and in controlled environments and contribute to risk analysis. Information from closely associated projects, which will continue the monitoring of pathogens in ears (Central Science Laboratory; Defra-funded, with HGCA) and mycotoxins in grain (Harper Adams University College; FSA/HGCA-funded), will feed into the project, substantiating the experimental findings, and make an essential contribution to risk analysis. Risk analysis will therefore be based on completed epidemiological information, including published research from overseas, together with previous UK survey data and up-to-date monitoring of crops and weather patterns. This will be used to develop models that will assess long-term risk, the risk of mycotoxin contamination of grain produced in the current year, or risk of severe disease in the current or following season’s crops. This is expected to contribute to policy and planning, and will lead to advice on choice of crop, tillage method and fungicide use, leading, at best, to toxin-free grain and grain products.
The relevance of the proposed research to Defra is in its contribution to the protection of the human and animal food chain from toxin contamination and to the sustainability of arable agriculture in the UK. The findings are expected to make an immediate contribution to policy decisions and, on the farm, to crop management advice and practice for minimising ear blight and mycotoxins. The situation in North America haThe situation in North America has had to be dealt with retrospectively, whilst in the UK we are still in a position to take preventive action.