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This work has characterised cultivar resistance to Fusarium head blight (FHB) and brown foot rot (BFR) in wheat caused by Fusarium culmorum. In vitro assays were used to investigate the relationship between phenotypic FHB resistance and possible mechanisms involving tolerance to deoxynivalenol (DON) and antifungal activity of protein extracts from grain. Quantitative trait loci (QTL) for individual components of FHB resistance were mapped in winter wheat using doubled haploid progeny lines (DHL) from a cross between Hobbit 'sib' and the FHB resistant cultivar WEK0609. In addition, the genetic relationship between QTL for FHB resistance and certain aspects of plant morphology, habit and yield was also assessed. Resistance to FHB and BFR was not correlated in the germplasm studied indicating that resistance to the two phases of the disease was independent . In general, AUDPC was a good indicator of relative yield and fungal biomass (F. culmorum-specific quantitative peR) at the ear, however, levels of fungal biomass at the stem base were frequently underestimated. Low correlation between FHB resistance, antifungal activity and in vitro DON tolerance, indicated that the mechanisms underlying such assays may be a relatively unimportant component of resistance in WEK0609. Significant correlation between visual and underlying measures of disease spread (relative yield and fungal biomass) suggests that resistance to colonisation dominates WEK0609 resistance. Classical genetics indicated that heritability for symptom development in WEK0609 was high (0.7 to 0.8) and based on two or three genes of additive effect. Major QTL for components of WEK0609 FHB resistance that reduced DON content and increased yield tolerance were detected on the long anns of chromosomes 2D and SA respectively. The QTL on SAL was associated with QTL for increased in vitro DON tolerance, awning, spikelet weight and plot yield, and reduced spike density. This is the first study to identify the genomic location of FHB resistance in winter wheat.

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An increasing human population is met with the challenge of feeding over 10 billion people by 2050. Nowadays, over 20% of crop production is lost to insect pests. Chemical control agents, in general, present broad-spectrum activity, killing both pests and beneficial organisms that would contribute to production (i.e. pollinators and natural enemies). Previously, the insecticidal voltage-gated calcium channel blocker peptide ω-ACTX-Hv1a (Hv1a) was linked to the ‘carrier’ molecule snowdrop lectin (GNA). The resulting fusion protein, Hv1a/GNA, is highly toxic towards lepidopteran and coleopteran pests, presenting potential for use as a biopesticide. Here, the fusion protein was shown to also be toxic to the hemipteran pests Sitobion avenae and Myzus persicae, via artificial diet and when expressed in transgenic plants. However, its effects on non-target arthropods have not been previously evaluated. Therefore, toxicity of Hv1a/GNA was tested against two beneficial insects, the parasitoid wasp Eulophus pennicornis via its host, Lacanobia oleracea, and the honeybee Apis mellifera. The fusion protein did not present any significant tri-trophic negative effects on E. pennicornis, even when injected into host larvae. Honeybee survival was slightly affected when fed on high doses of fusion protein representing a ‘worst-case scenario’, but lead to no detectable effects when dosed with field-relevant levels. The fact that bees internalized Hv1a/GNA led to the hypothesis that the haemolymph-feeding parasitic mite Varroa destructor would be affected by the fusion protein. However, mites were able to digest the protein and hence no effects were recorded. Further attempts to target calcium channels in M. persicae and Tribolium castaneum via RNAi were made. Whilst there were no phenotypic effects, gene expression was down-regulated in T. castaneum. This study shows that Hv1a/GNA is a specific biopesticide, posing low risks against beneficial non-target organisms while being toxic to selected insect pests.

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Light can become highly polarised when reflected from leaves. Polarisation-sensitive visual systems are very commonly found in insects, meaning it is possible that the polarisation of light reflected from plants may influence the behaviour of insects. This might result in the evolution of adaptive viral symptom~ which alter the polarisation properties of infected plants, in order to influence the attractiveness of infected plants to insect vectors and thereby enhance viral transmission. The primary aim of this project was to investigate whether plant viruses affect the polarisation of light reflected from leaves, and whether such effects may be different between insect vectored and non-insect vectored viruses. Given that surface features are a key determinant of polarised reflectance, the effects of viral infection on the expression of genes involved in the synthesis of leaf waxes and hairs was also analysed. It was found that two aphid vectored viruses, Potato virus Y and Cucumber mosaic virus, caused significant reductions in the degree of polarisation of light reflected from Nicotiana tabacum leaves, whereas Tobacco mosaic virus and Pepino mosaic virus, both non-insect vectored viruses, did not induce this effect. The aphid vectored viruses also induced more pronounced upregulation of leaf surface structure gene expression than the non-vectored viruses, in N. tabacum and Arabidopsis thaliana. Polarisation reflection was also analysed using a range of A. thaliana mutants deficient in the formation of leaf waxes or hairs, to establish whether these mutant phenotypes have any significant impacts on polarisation reflection. It was found that mutations in wax synthesis and leaf hair formation genes can significantly alter polarisation reflection from leaves. The impacts of viral infection on leaf wax structure and hair numbers were also analysed in wild type A. thaliana plants, although no significant differences between healthy and infected leaves were found in these experiments. Finally, a preliminary study was carried out to investigate the possible influence of polarisation signals on the behaviour of asexual wingless morphs of the green peach aphid, Myzus persicae, an efficient vector of many plant viruses. A series of choice tests were performed; however, these preliminary investigations did not reveal any differences in the attractiveness of wingless M. persicae to stimuli with differing polarisation properties.