Abstract/Summary

Published research showed there was a link between the abundance of septoria diseases (Zymoseptoria tritici and Parastagonospora nodorum) and sulphurous acid in acid rain. Historical records showed that P. nodorum was at a peak in 1970s while Z. tritici became more abundant at 1980s. Another, small scale, study showed that both pathogens were affected by sulphur, but Z. tritici was reduced more by sulphur than P. nodorum. These studies suggested it could be useful to investigate the effect of sulphur fertilizer under larger scale, field, conditions. Thus, the aim of this project was to study if sulphur fertilizer affects the abundance of these pathogens, and to study if sulphur fertilization alters the yield and quality of wheat under disease pressure. A further question was whether silicon fertilizer affects both pathogens and the yield and quality of wheat. A final aspect of this thesis was to develop a way to quantify pathogens by using qPCR assay on large field samples. A glasshouse experiment showed that all wheat cultivars were susceptible to available pure isolates of both pathogens, but the proportion of leaves infected by these isolates varied between cultivars. Cv. Paragon showed a high proportion of infected leaves in comparison with Gallant and Maris Huntsman (M. Huntsman). Three successive field experiments were conducted. Z. tritici infected all plots, so it was not possible to estimate changes in competitive effects due to the fertiliser regimes. In the field experiments a variety of measurements were used at different growth stages to assess the diseases. The proportion of leaves infected with, and disease severity of, Z. tritici were not significantly affectedly by sulphur fertilization in 2013. In two further experiments, proportion of leaves infected with, and spore concentration of, Z. tritici were reduced by sulphur fertilization. In the 2014-2015 experiment disease severity of Z. tritici was significantly reduced by sulphur fertilization. Although autumn spray and seed inoculation with P. nodorum did not succeed, a spring spray inoculation was successful in the 2014-2015 experiment. In this experiment, proportion of leaves infected and disease severity of both fungi were reduced by sulphur fertilization. but Z. tritici was reduced more than P. nodorum. These results agree with the historical trends. Yield and quality measurements results showed that sulphur fertilization increased yield and the wheat quality was improved. This result was obtained when the sulphur fertilization was split and applied at multiple times throughout the growing season of wheat (Table 6).