This thesis aims to characterise the structural, adhesion and release properties of polymeric microcapsules which are used ina griculture for t he controlled delivery of pesticides to crops. An adaptation of atomic force microscopy (AFM) known as chemical force microscopy (CFM) has been used to investigate the adhesion characteristics of functionalised polyurea microcapsules to surfaces. The adhesion properties of microcapsules (attached to AFM cantilevers) to self-assembled monolayers (SAMs) of alkyl thiols on gold have been investigated at the single capsule level, and as a function of polymer wall surface functionality. Measurements have been made to OHterminated, CH3-terminated and mixed CH3: COOH-terminated SAMs. The importance of microcapsule topography and elasticity on adhesion measurements has been discussed. The surface pK1I2 of a capsule with a surface modified with a sulfonateterminated molecule has been estimated using force titration methodology. The adhesion properties of functionalised microcapsules to the leaf cuticle of Prunus laurocerasus have been examined, highlighting areas of hydrophilicity on the surface of the leaf. The release properties of a ctive ingredients from p olyurea microcapsules into solution using confocal laser scanning microscopy (CLSM) have been investigated. Preliminary studies obtained the optimum species to use inside the microcapsule and the solution into which the species should be released. The release characteristics 0 f six varieties of microcapsule, differing in the wall thickness and cross linking density were examined and from the release profiles obtained, the product of the mass transfer coefficient and solubility coefficient could be calculated. The high resolution imaging capabilities of the confocal microscope have been demonstrated, providing detail on the structure of the leaf of the Prunus Laurocerasus plant and t he caterpillars Heliothis virescens and P lutella xylostella, two of t he most common pests, which the microcapsules of interest are aimed at controlling. The release properties to leaf surfaces of two types of polyurea microcapsules, which have different release mechanisms, were investigated using CLSM. Detailed release studies to model surfaces showed that one type of capsule (lambda cyhalothrin) released in the dry state and the other (emamectin benzoate) did not. A release rate was determined in the former case. A technique has been developed which is capable of visualising the release and diffusion of a species (Cd2+) from a hemisphere. Voltammetry has been used in conjunction with CLSM to monitor quantitatively and visually the preconcentration and release of Cd2+ into and away from a mercury hemisphere UME. The fluorescent indicator used was Calcium Green-5N, which is a cadmium-sensitive fluorophore that fluoresces upon binding Cd2+and can thus be detected by CLSM. A delay was observed between the release of C d2+ from t he hemisphere (determined voltammetrically) and binding to the fluorophore (visualised using CLSM).

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Two selective media which specifically allow the cultivation of Bacillus thuringiensis while it is in the vegetative as opposed to the spore form were developed. Using these media it was conclusively proved for the first time that B. thuringiensis can reside on the phylloplane in a metabolically active form. This was corroborated by evidence, also for the first time, that conjugation can take place on the phylloplane between such endemic strains. A new bacteriophage, infecting one of the endemic stains, which was activated by the process of genetic recombination, was isolated and characterized. The appearance of naturally occurring strains of B. thuringiensis in vegetative and spore form was followed over a growing season on clover (Trifolium hybridum) in the field. Simultaneous and sudden rises and declines of both spore and vegetative cell densities were observed. These could not be correlated with weather conditions. A genetically stable population of strains seemed to be maintained throughout the growing season. The most common other spore-former on these leaves was Bacillus cereus but the fluctuations in appearance of these two very closely related species were not co-incident. Using specific PCR primers, a considerably diversity of toxin types was found with the majority of isolates possessing multiple d-endotoxin genes. Bioassays against a lepidopteran insect (Pieris brassicae) of purified d-endotoxins showed that they were not more potent than those from a laboratory-adapted strain. A high percentage, however, of the endemic isolates (82%) possessed the ‘Vegetative insecticidal protein’ (Vip) gene, vip3. This might indicate an involvement of Vips in the establishment of these strains on the phylloplane. A mechanism for colonization of annual plants by B. thuringiensis was demonstrated for the first time. It was shown that spores added to seeds, even in non-sterile soil, can germinate and replicate on the resulting seedlings. The level of colonization achieved did not have a consistent influence on the feeding behaviour of third instar larvae of P. brassicae which were present on the plants for three days. Nevertheless, the fact that the number of CFU of B. thuringiensis recovered per gram of insect increased with time is evidence of proliferation of the bacterium inside the insects. Four isolates of B. thuringiensis that had been recovered in the vegetative phase from the phylloplane of T. hybridum were grown for 500 generations in a rich medium. Changes were observed in all of the strains but one isolate changed remarkably in all of the characteristics assessed which included: structure; plasmid profile; fatty acid composition; and d-endotoxin production. Moreover, the sequence of the Vip3 protein harboured by the evolved strain showed changes when compared with that of the parental strain.

The present study evaluated the effect of three host plants: chickpea, Cicer arietinum, tomato, Lycopersicon esculentum and cotton, Gossypium hirsutum, on the efficacy of Helicoverpa armigera nucleopolyhedrovirus (HearNPV). The results showed that HearNPV was inactivated within one hour when sprayed on to the leaf surface of chickpea indicating that leaf surface factors on this plant were responsible for the effect. In contrast, virus that has been sprayed onto the leaf surface of cotton and tomato was not significantly affected compared to untreated HearNPV. This study also showed that HearNPV was inactivated on the chickpea leaf surface in field experiments. One compound was shown to be induced on the chickpea leaf surface in response to spraying with 0.02% Triton X-100 which was used as a surfactant. The induced compound was isolated and identified as sissotrin, and isoflavonoid. Sissotrin was shown to reduce the efficacy of HearNPV, although not by as much as when the virus was exposed to the chickpea leaf surface. The results indicated that sissotrin was partially responsible for the inactivation of HearNPV and that other compounds which accumulated on the leaf surface after spraying with HearNPV must also have an additional effect in combination with sissotrin. This is the first study to show that isoflavonoids reduce the efficacy of baculovirus against Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Field trials were also conducted with different low cost additives mixed with HearNPV on chickpea crop and these increased the efficacy and persistence of HearNPV under field conditions. This study may therefore help to improve biopesticide based pest management on chickpea.

In this study, all Scottish post 1980 Najas flexilis sites were surveyed for the presence or absence of Najas flexilis. In addition, all pre 1980 mainland sites were visited and 10 Irish sites across the Irish geographic range and presence or absence of Najas flexilis recorded. The environmental conditions required for Najas flexilis growth, including water and sediment chemistry, light and exposure were evaluated. These environmental conditions are compared between present and extinct sites. Measurement of specific plant traits, leaf area and reproductive number, from a representative sample of the population is used as a method for assessing the condition of the population in response to the environment. Models show that the concentration of phosphate in the sediment and water and magnesium in the water, along with the alkalinity and either light or calcium in the sediment can predict 67 - 88% of the variation in the plant traits of Najas flexilis. The community in which Najas flexilis grows was recorded from all sites visited. Two approaches were used a quantitative micro-habitat approach which is concerned only with the plants growing in the immediate vicinity of Najas flexilis and a qualitative whole lake approach. The suitability of these two approaches as a site condition monitoring tool for Najas flexilis is considered. The applicability of the Standing Water Type (SWT) classification to the community groups attained from whole lake approach and the applicability of National Vegetation Classification (NVC) scheme to the community groups attained from micro-habitat approach is considered. The lake scale qualitative approach elucidated significant differences in lake water pH, alkalinity and the concentration of total oxidised nitrogen and dissolved reactive phosphate in the water as well as differences in phosphate, calcium and iron in the sediment.

The flora of Crete in its multifarious micro-landscapes offers the possibility of selecting native species with high ornamental value for use in urban landscapes and commercial horticulture. To assess this potential eight species were selected: Staehelina petiolata, Ptilostemon chamaepence, Otanthus maritimus, Prasium majus, Convolvulus dorycnium, Campanula pelviformis, Sternbergia sicula and Colchicum macrophyllum. The biological cycle in situ, sexual and asexual propagation as well as their cultural requirements and adaptability in urban landscape were studied. In addition to identifying the light and temperature requirements for seed germination of the species, Other factors were important including after-ripening for P. chamaepence and S. petiolata, scarification for P. majus and C. dorycnium and imbibition in 20°C for C macrophyllum and S. sicula. Propagation by stem cuttings was influenced by mist, addition of IBA, the season and the substrates. IBA solutions at 4000, 2000 ppm and 2000 ppm in powder promoted on rooting of S. petiolata, P. chamaepence and P. majus stem tip cuttings with the highest rooting level of 50, 70 and 72%, respectively, while both IBA at 0 or 2000 ppm on Otanthus maritimus produced 100% rooting. Best substrates were peat-moss+vermiculite, vermiculite, sand and vermiculite and best seasons autumn, spring or late autumn, early summer, and spring for Staehelina. Ptilostemon, Otanthus and Prasium, respectively. Cross-cutting and BA on the base of Sternbergia sicula increased the bulblets from 1-3.5 to 12.8 and 13.5 per bulb yearly, respectively. Colchicum macrophyllum had a very low asexual reproductive activity producing one corn per year. The wounding of the replacement bud stimulated development of the reserve bud so that each corm could produce two or more cormlets. Morphogenesis was achieved in vitro by the affect of BA; callogenesis and rhizogenesis by NAA, and rhizogenesis by IBA on S. petiolata and P. chamaepence seedlings. Adventitious bulblets and plantlets formed on scales and clumps of shoots of S. sicula by the addition of BA and NAA producing over 20 bulblets per bulb. 2,4-D, BA, NAA and combinations produced callus, shoots and new corms on buds of C. macrophyllum. All studied species were established successfully in pots and in an urban landscape. The ornamental characteristics and use of eight species was determined and a master plan was designed using indigenous plants of Crete.

As the demand for energy rises, Populus species are increasingly grown as bioenergy crops. Meanwhile, due to global change, predictions indicate that summer droughts will increase in frequency and intensity over Europe. This study was carried out to evaluate the adaptation to drought in Populus, at different levels: genetic, genomics and physiology. Forests trees such as poplar are very important ecologically and economically but the Populus genus is known to be drought sensitive. Consequently, it is essential to understand drought response and tolerance for those trees. Two populations of poplar were used for this study, a mapping population (Family 331) and a natural population of Populus nigra. The F2 mapping population obtained from a cross of Populus deltoides and Populus trichocarpa, showed differences in stomatal conductance and carbon isotope composition in both clones and the F2 progeny. It was also used to discover QTL related to water use efficiency highlighting interesting areas of the genome. Combining QTL discovery and microarray analysis of the two clones in response to drought, a list of candidate genes was defined for water use efficiency. The natural population of Populus nigra consisting of 500 genotypes of wild black poplar showed variation in numerous physiological measurements such as leaf development and carbon isotope discrimination in well-watered conditions depending on their latitude of origin. The drier genotypes (from Spain and South France) had the smallest leaf area which could be linked to an adaptation to drought. Physiological measurements of extreme genotypes in leaf size of this population revealed differences in response to water depending on their latitude of origin. Stomatal conductance rapidly decreased and water use efficiency improved for Spanish genotypes after a slow and moderate drought stress. Direct comparisons between the transcriptome of extreme genotypes from Spain and North Italy in well watered and drought conditions provided an insight into the genomic pathways induced during water deficit. Six candidate genes were selecting for further analysis using real-time PCR: two stomatal development genes (ERECTA and SPEECHLESS), two ABA related genes (ATHVA22A and CCD1), a second messenger (IP3) and a NAC transcription factor (RD26)

The increasing losses of potato tubers in storage due to soft rot spoilage have emphasised the need for detailed studies of the entry and spread of the pathogen and the action of the defence mechanisms of the potato at an ultrastruotiiral level. The studies have shown that the tuber may be infected through fresh wounds or lenticels under conditions of high relative humidity, providing sufficient inoculum is present and, in the case of lenticels, the conditions before inoculation have been suitable. The effects of the environment on the physical barriers and consequently bacterial spread are complex. Observation of the formation of suberin and melanin at the infection interface hafe shown that the former may hinder bacterial spread: the role of the latter is more obscure. Light microscopy has shown that the pattern of initial colonisation is highly temperature dependant. Colonisation through lenticels is quicker at first than through fresh wounds probably due to the differences in anatomy, although quantitatively large amounts of inoculum are involved in the latter under most conditions. Once inside the tuber the bacterium spreads through the storage parenchyma as zoned colonies aligned in one direction during the early stages, but after the host cells have been macerated the cells of the pathogen become uniformly distributed between the pcl&tc cells. Vascular spread is less common, and the bacteria are enclosed in the xylem and phloem by the suberised, closely packed cells of the vascular parenchyma, although some pectolysis and subsequent melanin formation occurs outside the bundles for distances of up to 500 u. Tissue degradation involves the destruction of the cytoplasm, as well as the cell wall. Characteristically membrane rupture is associated with the enlargement of microbodies. Although cells containing calcium oxalate monohydrate are colonised intracellularly, the crystals do not appear to be utilised. The significance of these findings in relation to the disease as a whole are discussed, and possible practical implications for the grower and user of potatoes are considered.

Consumer awareness of food nutritional properties has increased significantly. A healthy diet is now viewed as the first step towards the prevention of many age-related chronic diseases such as cancer and heart disease. In most cases oxidative damage is involved in the onset of these diseases, much of which can be prevented by a diet high in antioxidants. However, throughout hundreds of years of domestication, many crop species, such as lettuce, have been genetically manipulated with the purpose of increasing favourable traits. These selective processes have resulted in the unintentional decrease of the antioxidant nutritional content of species such as Lactuca sativa. This project aimed to use natural resources for the enhancement of lettuce nutritional properties through the introgression of genes from a close relative of L. sativa. Initially, the total antioxidant content of baby lettuce leaves was investigated, with particular focus on carotenoids, chlorophyll and phenolic compounds. Wild lettuce (L. serriola, acc. UC96US23) was found to produce higher levels of total antioxidants, chlorophylls and carotenoids than the lettuce cultivated variety, Salinas cv. Subsequently, these traits were analysed in a Recombinant Inbred Line mapping population obtained by crossing these two lettuce species. Considerable transgressive segregation was observed and this data was then used to map Quantitative Trait Loci (QTL) on the population, which showed an additive effect of both parents contributing to these beneficial traits. Subsequent analyses of key genes involved in the synthesis of carotenoids and phenolic compounds revealed the presence of single nucleotide polymorphisms. Understanding the processes involved in the synthesis of nutritional properties and identifying the genes underlying these traits is key to producing a better quality lettuce. This project demonstrates potential for the improvement of lettuce antioxidant nutritional qualities through breeding with a wild relative

Biofortified orange-fleshed sweetpotato (OFSP) is being promoted to tackle vitamin A deficiency, a serious public health problem affecting children and pregnant/lactating women in sub-Saharan Africa. The aim of the study was to quantify and understand the factors influencing carotenoid losses in dried OFSP. Losses were determined in chips after drying and storage. A preliminary study demonstrated that carotenoid levels were not significantly different following either solar or sun drying. Carotenoid loss after drying was generally correlated with high initial moisture content and high carotenoid content in fresh sweetpotato roots. Losses of pro-vitamin A were less than 35% in all cases. Flour made from OFSP could therefore be a significant source of provitamin A. In contrast, storage of chips at room temperature in Uganda and Mozambique for four months resulted in high losses of pro-vitamin A (ca. 70-80% loss from the initial dried product). Low-cost pre-treatments, such as blanching, antioxidants and salting, did not reduce carotenoid losses during storage. Enzymatic catabolism of b-carotene in dried OFSP was considered unlikely because of low peroxidase activities at low water activities and the loss of peroxidase activity during storage. To understand further the factors causing the losses, dried sweet potato chips were stored under controlled conditions of temperature (10; 20; 30; or 40ºC), water activity (0.13; 0.30; 0.51; 0.76) or oxygen (0 [under nitrogen]; 2.5; 10 or 21% [air]). Oxygen was the main cause of degradation followed by temperature. An Arrhenius kinetic model was used to show that carotenoid breakdown followed first order kinetics with an activation energy of 68.3kJ.mol-1 that was in accordance with the literature. Experimental observations fitted well with data predicted by the kinetic model. The formation of the volatile compounds,b-ionone; 5,6-epoxy-b-ionone; dihydroactinidiolide; b-cyclocitral that were clearly related to the degradation of b-carotene, helped further understand breakdown patterns of b-carotene.