description
- The foundation of global food security is built on the three cereals wheat, rice and maize, where wheat is the leading source of vegetable protein in human food. In the UK this cereal is the most important crop grown with an annual value of about £1.2 billion. The average yield of wheat in the field in the UK is currently 8.4 tonnes/ha, but this yield is dependent on high levels of mineral fertilizer (especially Nitrogen, Phosphorus and Potassium) and pesticide usage. Nitrogen (N) fertiliser use is of concern because it is associated both with high levels of energy use and greenhouse gas emissions (e.g. CO2, N2O) that cause climate change, in addition to eutrophication of fresh water and marine ecosystems. However, nitrogen fertilisation is required for achieving high yield in wheat, and increasing sustainability through decrease in nitrogen input is not commercially feasible due to the resulting fall in yield. Given that high-nitrogen nutrient regimes are reality in the field, decreasing pesticide usage is a target for enhancing sustainability of wheat production. An undesirable side-effect of nitrogen fertilisation is that it increases susceptibility to pathogens. There is increasing evidence that high soil nitrogen enhances the development of fungal pathogens such as Septoria that causes wheat leaf blotch disease (Simón et al 2003; Loyce et al 2008). The mechanisms leading to these nutrient induced changes in disease development are not known. Septoria leaf blotch (STB) is currently the most important disease of wheat in Europe and is among the top three most economically damaging diseases of this crop in the United States. Despite the importance of STB, there is very little information available on the defence mechanisms or immune responses that allow wheat to counter Septoria infection. Fungicides provide the only control measure for this devastating disease, but extensive applications of fungicides increase the worldwide economic costs attributed to STB. In addition, STB outbreaks are becoming more prevalent as currently available fungicides are becoming less effective against new resistant strains of Septoria. Therefore there is an urgent need to develop new strategies to combat STB in the field. The industrial partners (KWS) in the proposal recognise that exploiting endogenous defence mechanisms that do not rely on fungicides may provide an alternative method to control this disease, and that an understanding of why Nitrogen nutrient level and disease resistance are inversely correlated is likely to lead to strategies which will enable exploitation of endogenous defence. Our preliminary data have suggested that a family of transcription factors (Tfs), the WRKY genes that have been shown to be central to plant defence in model systems, form a link between nitrogen input and Septoria disease resistance in the field. We propose to investigate the roles of these WRKY gene family TFs to reveal the identity of the specific WRKYs which are critical for Septoria resistance in the field under varying nitrogen levels and mechanisms which can be exploited to boost Septoria resistance under the high input growth conditions necessary for maintaining yield. The overall objective of this project is to gain an understanding of how the nutrient regime under which cereals are grown affects their susceptibility to STB disease, with the ultimate aim of manipulating this relationship to allow enhanced disease resistance to be retained under high or optimum nitrogen input growth conditions.