Abstract/Summary

The threat to UK food security due to cereal diseases is serious. Diseases can affect crops and have a serious impact on the economic output of a farm and on food. Among cereal diseases, Fusarium Head Blight (FHB) and Fusarium Crown Rot (FCR) disease are two of the most widespread and damaging diseases of cereal crops. This thesis reports the effect of Piriformospora indica on Fusarium diseases of wheat, both head blight and crown rot, with the purpose of developing a solution to control crop diseases by using natural microorganisms. Piriformospora indica is a root endophyte belonging to the Sebacinaceae (Sebacinales, Basidiomycota). It was originally found in the Thar desert of Rajasthan, in India. P. indica forms mutualistic symbioses with a broad range of host plants, increasing their biomass production and resistance to fungal pathogens. Glasshouse experiments and controlled environmental chambers with conditions adjusted to UK autumn conditions were used to determine the effect of P. indica on FCR disease of wheat, both Fusarium culmorum and F. graminearum. P. indica reduced damage to wheat seedlings by restricting growth of pathogen in the root. The effect of P. indica on FHB disease of winter (cv. Battalion, NABIM group 2) and spring (cv. Paragon, Mulika, Zircon (NABIM group 1), Granary, KWS Willow (NABIM group 2) and KWS Kilburn (NABIM group 4)) hard wheat and subsequent contamination by the mycotoxin deoxynivalenol (DON) were examined in the pots under UK weather conditions. P. indica application reduced FHB disease severity and incidence and mycotoxin DON concentration of inoculated winter and spring wheat samples. P. indica also increased above-ground biomass, thousand grain weight and total grain weight. The effects were similar at different fertiliser levels. The effect of P. indica was compatible with the arbuscular mycorrhizal fungus Funneliformis mosseae and foliar fungicide Aviator Xpro (Bayer CropScience, UK; with active ingredients of prothioconazole and bixafen) application. P. indica reduced severity and incidence of naturally arising infection by Septoria leaf blotch (caused by Zymoseptoria tritici), yellow rust (caused by Puccinia striiformis f. sp. tritici) and powdery mildew (caused by Blumeria graminis f.sp. tritici). The nutrient analysis of soil and plant tissue samples showed that P. indica did not have any effects on phosphorus, nitrogen and potassium status and uptake were not significantly affected by P. indica inoculation. P. indica mRNA for the elongation factor (TEF gene) was used as an indicator of P. indica viability in soil. P. indica was still alive after four and eight months in pots of soil from the Reading area, which had been left open to winter-summer weather conditions without host plants, but not after 15 months. PCR-denaturing gradient gel electrophoresis of DNA extracted from root zone or from bulk soil, in which P. indica-infected wheat had been grown, showed P. indica increased the root and soil fungal and bacterial species diversity. Test on arable weeds, black-grass, wild-oat and cleavers, showed that on average over species P. indica increased root biomass by 35 %; but above-ground biomass was not significantly affected by P. indica. The average above-ground competitiveness of the weeds with wheat was slightly decreased. My results suggest that P. indica could be used to control wheat diseases in field settings in the UK. However, extensive data would be needed to determine ecological and agronomical safety and persistence, before release on a field scale was commercialised.