Cold conditions during imbibition can result in slow or no germination in some maize seed, leading to sub-optimal crop density and uniformity and loss of yield. A novel seed treatment is required that restores germination in seed batches that perform poorly under cold conditions. Germination of seed batches from different varieties was characterised following imbibition under cold conditions which permit no or slow germination. Hydroxamic acid inhibitors of 9-cis-epoxycarotenoid dioxygenase (NCED) stimulate germination through ABA biosynthesis inhibition in other species and had a small significant effect in increasing the proportion of normal seedlings after cold imbibition. This indicated that normal germination of maize may be inhibited by dormancy-related mechanisms during or after imbibition in cold conditions. The maize NCED (ZmNCED) family was characterised. D2 and D4 inhibit other enzymes in the carotenoid cleavage dioxygenase family and exhibit relatively weak inhibition of NCED. ZmNCEDs were cloned for in vitro enzyme inhibition studies to aid identification of NCED-specific inhibitors. An RT-qPCR assay for measuring ZmNCED expression was developed. Seed ZmNCED expression and ABA concentration was elevated under cold conditions, compared to optimal germination conditions. An assay was developed to screen for germination stimulating compounds. 965 of a diverse library of 5074 compounds were identified as potential germination stimulators. Germination stimulating activity was replicated in 171 of these compounds, with some more efficacious than D4. Germination stimulating activity of 88 compounds related to the current lead compound, D4, was assessed at concentrations of 10 ppb to 10 ppm. Compounds were identified that, at less than 10 ppm stimulated germination more than D4 at 312 ppm. The mode-of-action of these compounds will need to be determined and may yield novel targets for germination stimulation. Thus novel seed treatments for improving germination of low vigour maize seed lots under cold conditions could be based on NCED inhibition or the action of the newly identified compounds.

This study evaluated sweetpotato resistance to sweet potato weevils (Cylas spp.) and investigated the phytochemicals that mediated this defence. New Kawogo, LIR302 and ARA228 were shown to be the most resistant based on stem and root damage. Significant differences were observed on the number of faecal droppings, feeding holes and eggs laid on the root in a choice and no-choice bioassays confirming that New Kawogo, LIR302 and ARA228 affected development and emergence of adult weevils. Six hydroxycinnamic acid esters, including hexadecylcaffeic, hexadecylcoumaric, octadecylcaffeic, octadecylcoumaric, heptadecylcaffeic and 5-O-caffeoylquinic acid esters were identified on the root surface and amounts of these differed significantly between resistant and susceptible varieties. The mean number of C. puncticollis and C. brunneus feeding holes, faecal droppings and egg laid on the root core were significantly different among the root cores treated with synthetic hydroxycinnamic acid esters. The study also showed that there were significant differences in the root volatiles of resistant and susceptible variety both before and after infestation. The larval survival of sweetpotato weevil was significantly affected by hydroxycinnamic acid esters treatment and Bt-toxin applied on the diet. There was also significant differences in percentage sweetpotato weevil root infestation among genotypes of the segregating population. The genotype by environment (GxE) interaction effect was also significant on the sweetpotato weevil damage on the stem portion of the sweetpotato vine indicating that weevil stem damage is dependent on the season. The mean number of sweetpotato weevil feeding holes differed significantly on the root of the genotypes of the segregating population in the feeding and oviposition bioassay. There was significant difference in total hydroxycinnamic acid (HCA) esters among the genotypes of the segregating population. The distribution of genotype mean total HCA ester concentration was skewed to the left and only one progeny, NKB257, had higher total HCA ester concentration than New Kawogo, the resistant mother used in the crossing. A weak but significant correlation between total HCA ester concentration and sweetpotato weevil root damage was observed signifying that resistance to sweetpotato weevils depended on other factors as well. The results are discussed in terms of how they might be incorporated into integrated pest management of sweetpotato weevils.

Insect specific viruses like nucleopolyhedrosisvirus (NPV) can provide an alternative and effective insect pest control compared to conventional chemicals; however, on certain crops like chickpea efficacy of the virus is limited. Previous studies have demonstrated that inactivation on chickpea was leaf surface based and rapid, however, the compound identified (isoflavonoid, sissotrin) could not account for the total inactivation that was recorded on chickpea leaves. The present study investigated further the legume-NPV insect interaction, with aim of identifying conclusively the compound(s) responsible for NPV inactivation on chickpea, and also to determine if the same plant chemistry also occurs on two other major African and Asian legumes, cowpea and pigeonpea, and to understand the mechanism involved. Laboratory results showed that chickpea leaf surface was more inactivating to NPV than cowpea or pigeonpea. Although both cowpea and pigeon also reduced the efficacy of NPV the effect was relatively small. Bioassays with the isoflavonoids (biochanin A and formononetin), identified to be present or induced at higher levels after spraying with HearNPV, showed that although both compounds significantly reduced NPV efficacy, the effect was modest compared to that recorded on chickpea leaves. When the most abundant chickpea acids (malic and oxalic) were mixed with different concentrations of the isoflavonoids and tested on NPV, significant inactivation was observed which was comparable to that obtained on chickpea leaves. The inactivation of NPV by the combination of chickpea acids plus isoflavonoids was not dependent on high concentrations of isoflavonoid tested, suggesting that chickpea acids alone could be responsible. Therefore, further tests were carried out to determine the role of the acids alone on NPV. The most abundant chickpea acids were prepared at different concentrations and tested with the virus at high lethal concentration. The results showed that chickpea acids alone were responsible for the inactivation of NPV, and among the two acids tested, oxalic was found to be more active against the virus. Although the inactivation was shown to correlate negatively with pH of the acids, the results suggest that oxalic acid was exerting its effect independently of the pH. This is the first study to demonstrate that organic acids of chickpea were responsible for inactivation of NPV. The findings from this study will be helpful in identifying suitable formulation additives to improve the field persistence of NPV on chickpea and other crops.

The African coffee white stem borer, Monochamus leuconotus (Coleoptera: Cerambycidae) is a serious pest of Arabica coffee in Zimbabwe and other African countries. Very was known about the chemical ecology of M. leuconotus prior to the initiation of the studies described in this thesis. The objectives of this work were to investigate the mating behaviour in order to look for evidence of the existence of chemical interactions between conspecific beetles and host plants. Mating behaviour and daily activity patterns of adult M. leuconotus were characterised under laboratory and semifield conditions. Mating was initiated after the male encountered a searching female and touched her with antennae or tarsi. The activities of feeding, walking, mounting and copulation were mostly done during daylight hours with the exception of oviposition, which occurred at night. Laboratory bioassays conducted to determine whether contact pheromones played a role in mate recognition showed that males were able to complete the full sequence of behavioural activities involved in mating with both live and dead conspecific females. Males did not respond to dead females washed with hexane, and the responses could be partially restored by recoating the washed females with the hexane washings, indicating that cuticular hydrocarbons are important for recognition of sex and species. A laboratory bioassay was developed for evaluating the olfactory response of M. leuconotus to different cues. Females responded positively to coffee leaves, coffee bark scrapings and the synthetic male-specific compound of M. leuconotus dispensed in a sachet while males responded positively to coffee bark and to a combination of coffee leaves and the synthetic male-specific compound dispensed in a vial. Field trapping trials were conducted in Zimbabwe using live insect baits and the synthetic male-specific compound of M. leuconotus dispensed in polyethylene sachet and vials and different trap designs. Significant numbers of beetles were captured in traps baited with the male-specific compound, and numbers caught were further increased when certain host-plant volatiles were added, particularly (R)-(-)-linalool and methyl salicylate. Intercept panel traps and MK2 rat traps were effective in retaining insects caught. Floral surveys conducted around coffee fields to identify alternative host plants did not give conclusive evidence on the existence of alternative host plants although suspected coffee stem borer symptoms of attack were observed on previously reported alternative host plants. Feeding and oviposition studies suggested that female M. leuconotus feed mostly on Rubiaceae and preferred to lay eggs on Coffea arabica, G. ternifolia, V. infausta and K. venosa. The implications of the findings in relation to possible application of chemical ecology in management of M. leuconotus are discussed.

The cabbage whitefly, Aleyrodes proletella, has in recent years become a primary pest of several brassica crops in Europe. In the UK, its greatest impact has been on kale, where nymphs, wax deposits and sooty mould caused by honeydew excretion reduce the marketable portion of the crop, particularly later in the year. In order to test the contribution of insecticide resistance to these outbreaks, a leaf-dip bioassay method was developed. Resistance to several pyrethroids was found in multiple populations in Lincolnshire and Kent, with similar patterns between compounds but differing magnitudes of resistance. This resistance was expressed to a similar degree by both adults and nymphs. The host plant used in bioassays influenced lethal concentrations but not resistance factors. A diagnostic concentration of lambda-cyhalothrin was identified and used to screen further populations over successive years. No cross-resistance to neonicotinoid insecticides was evident in highly pyrethroid-resistant populations. Bioassays with the synergist piperonyl butoxide provided no evidence of mixed-function oxidase or associated nonspecific esterase involvement in pyrethroid resistance. Attempts to sequence the sodium channel gene of susceptible and resistant whiteflies to check for target-site resistance were unsuccessful. Field surveys of whitefly populations on wild cabbage were carried out to identify candidate native biological control agents for use in IPM strategies in field crops. These identified several parasitoid wasps and a coccinellid beetle, Clitostethus arcuatus. One of the parasitoids, Encarsia tricolor, and C. arcuatus were successfully cultured at NRI and tested in outdoor cage trials. In 2011, a multiple generation trial demonstrated the superiority of parasitoid release during the development of the first generation of whiteflies over later releases of E. tricolor or C. arcuatus. A Horticultural Development Company funded field trial in 2012 showed that insecticide application early in a whitefly infestation could provide prolonged control equivalent to regular spraying. This research will contribute to the development of future integrated pest IV management programmes for A. proletella through avoiding ineffective pyrethroid applications, facilitating insecticide resistance management and identifying non-chemical approaches.

Investigations have been carried out into the occurrence and functions of acid hydrolases during plant cell division, differentiation and senescence using histochemical and biochemical procedures. Statistical analyses of histochemical data have shown that particles staining for naphthol AS BI phosphatase in dividing unfixed root cells of Vicia f aba do not act as a 'trigger 1 in the way suggested for animal cells, since there were significantly greater numbers of particles in mitotic cells as opposed to interphase cells in all 3 root tissues, apical initials, procortex and central cylinder. Increasing the length of incubation time markedly increased the number of particles in all 3 tissues. The procedure for determining ft -glycerophosphatase activity in glutaraldehyde-fixed root tips was found to be unsatisfactory since cells in sections of tissues incubated without substrate contained lead-staining particles and in both test and control sections diffuse cytoplasmic and nuclear staining were apparent. Using the histochemical reagents, naphthol AS D acetate and the diazonium salt, fast red violet LB salt, a biochemical study of non-specific esterases extracted from broad bean root tips, has shown that these enzymes have an estimated Km of 0.07 mM, a pH optimum of 5.5 and that they lose substantial activity when dialysed against distilled water as opposed to 5mM magnesium chloride and 10mM phosphate buffer. However, adding magnesium and/or chloride ions to the assay system reduced enzyme activity. A combined cytochemical and biochemical analysis of non-specific esterases in differentiating root tissues of the broad bean showed that maximal enzyme activity, expressed on a per segment, per unit protein or per unit area of average-sized section basis, occurred within the zone of cell expansion, elongation and differentiation of procambial tissues. Cytochemical studies showed that in glutaraldehyde-fixed roots activity was only slightly inhibited when compared with unfixed material, whereas biochemical studies revealed that only about ⅛ of the activity of enzyme extracted from unfixed roots was 8 present in homogenates of fixed roots. In a study of non-specific esterases in soft fruit ripening and senescence, cytochemical studies demonstrated that enzyme activity was associated with subcellular structures in the pulp cells of the ripening strawberry. The fleshy mesocarp tissues of raspberry and blackberry, however contained no enzyme end-product at any of the stages of ripening examined. In older strawberry receptacles, also examined biochemically, enzyme end-product was associated with large spherical lipid-dropletlike bodies absent in younger receptacles. Assays of non-specific esterases in immature, maturing and mature pulp tissues showed that these enzymes increased several fold during ripening when expressed on a per g fresh weight or per berry basis. Although esterase activity changed little during the transition from 'maturing 1 to 'mature 1 when expressed on either basis, the specific activity of the enzymes fell markedly. The Km values of enzyme extracts from the 3 stages of berry development decreased as ripening proceeded denoting an increased affinity of these enzymes for their substrates possibly due to the removal of an inhibitor or a change in iso-enzyme pattern. Esterases from the three ripening stages exhibited broad pH optima (pH 5-5 - 6.5) although limitations of the assay procedure prevented the detection of possible alkaline optima. Ultrastructural studies showed that changes in the subcellular organelles of ripening strawberry pulp cells were similar to that reported for other senescihg.plant material, vesiculation of many organelles and loss of ribosomal material being the most characteristic. Attempts to localise esterases in fruit cells at the ultrastructural level were unsuccessful since electron dense end-product of diazotised lead phthalocyanin bound to a variety of structures even in the absence of the enzymes’ substrate. In contrast the use of the diazotate of LPED in Vicia faba root cells was more promising in that in test tissue end-product was found in small vacuoles and rough endoplasmic reticulum, whilst control cells incubated in the absence of substrate lacked enzyme end-product. The water-soluble epoxy resin, Durcupan, was assessed for its effect on plant cell organelle morphology by comparing similar tissue conventionally dehydrated in alcohol. No gross changes in ultrastructure were observed.

Tsetse (Glossina spp.) transmit species of Trypanosoma which cause trypanosomiases in livestock and humans. To improve the cost-effectiveness of baits used to control tsetse, studies were made of the host-oriented behaviour of the following Palpalis-group species: Glossina tachinoides and G. palpalis gambiensis in Burkina Faso, G. p. palpalis in Côte d’Ivoire, G. fuscipes quanzensis in the Democratic Republic of the Congo, and G. f. fuscipes in Kenya. In each country, electrocuting grids and traps were used to quantify the responses of tsetse to natural and artificial host stimuli. The results showed that riverine tsetse respond to certain natural host odours. For example, studies of the numbers of tsetse attracted to traps or grid baited with natural host odours showed that cattle odour doubled the catches of G. p. gambiensis and increased the numbers of G. tachinoides by five-fold; pig odour increased the catch of G. p. palpalis five-fold and doubled the numbers of G. f. quanzensis; and lizard odour doubled the catch of G. f. fuscipes. Responses of G. tachinoides and G. p. gambiensis to natural host odours were due largely to kairomones identified for savannah-tsetse (carbon dioxide, 1-octen-3-ol, acetone and 4-methylphenol). For instance, blends of 3-n-propylphenol, octenol, 4-methylphenol and acetone increased catches of G. tachinoides about five-fold, it doubled the catches of G. p. gambiensis and increased the catches of G. p. palpalis about 1.5-fold. Comparable catch ratios were obtained when acetone was removed from the blend; both G. tachinoides and G. palpalis were attracted by CO2. None of these chemicals was effective for G. f. fuscipes, suggesting that unidentified semiochemicals are present in lizard odour. For G. f. fuscipes, the response of female flies increased from 18% to 24% with lizard odour, but mammalian odours did not have any affect. For G. tachinoides the landing response increased significantly with cattle odour in one experiment only, and none of the odours had any effect in the landing responses for other species. The use of odours in control operations is discussed. Studies of visual stimuli showed that large targets (1m2) doubled the catches of G. p. palpalis and G. f. fuscipes compared to 0.25m2 targets, the smallest being eight times more cost-efficient. Horizontal oblongs were more attractive than vertical ones for G. f. quanzensis and vice versa for G. p. palpalis. For all species, square targets were as effective as the most attractive oblong. Landing responses were generally about 30%, and although consistently higher for larger targets, differences were not statistically significant. The addition of flanking nets increased the catches about four-fold. In conclusion, results suggest that cost-effective control of Palpalis-group tsetse could be achieved by using tiny targets (0.25×0.25m) flanked by nets of the same size.

This thesis critically examines the determinants of uptake of pro vitamin A-rich sweetpotato along the value chain in Uganda and examines the role of a marketing component in a food biofortification intervention. It is conceptualised within the value chain and adoption decision theory. Using both qualitative and quantitative methods of social investigation, this thesis: i) evaluates the factors that influence producers to grow Orange Fleshed Sweetpotato (OFSP) for sale, ii) assesses the factors influencing trader decisions to sell OFSP, iii) analyses factors determining acceptability and repeat purchase of OFSP by consumers, and iv) evaluates the role of marketing in a biofortification intervention. The thesis identifies both generic and specific factors influencing uptake of OFSP. Generic factors include: access to productive resources; previous experiences in marketing other crops; and importance of the crop. The specific factors were the role of the Reaching End Users (REU) project; the attributes of OFSP; price and profitability; the possibility of selling OFSP vines; and availability of OFSP roots. Six possible roles for marketing in a biofortification programme have been identified. These are: changing the perception of the crop, increasing uptake and adoption, exploring alternative uses, stimulating rural entrepreneurship, increasing availability and creating awareness and demand for the crop. It is recommended that biofortification interventions should have a marketing component, there is need to target mothers and children. Initial market development should focus on small market outlets. It is important to increase availability of OFSP and awareness of its benefits to human health along the value chain. Further research could focus on marketing of other types of biofortified crops, understanding variety specific drivers of OFSP and options for their promotion to specific end-users, developing and dissemination OFSP varieties with longer in-ground storage traits, and understanding the role of informal trade in driving uptake of biofortified crops.

Aquaculture is an important protein source for Malaysia. However, the susceptibility of fish to disease leads to heavy losses and hinders production. A potential solution is the supplementation of diets with prebiotics: non-digestible carbohydrates which improve growth and health by modulating gut microbiota to favour beneficial bacteria. Resistant starch (RS) is a prebiotic commonly fed to terrestrial animals, but little work has been performed on aquatic animals. Therefore, this study investigated the use of RS isolated from underutilized crops as a prebiotic in fish. Six species of underutilised legumes (adzuki beans, mung beans, black-eyed peas, pigeon peas, Bambara groundnuts and red lentils) were used for starch isolation via alkaline steeping, followed by processing involving enzyme or acid hydrolysis, and lastly gelatinisation and retrogradation to increase RS yield. Starch was isolated with yields of 25 – 40%, while enzyme hydrolysis pre-treatment was more effective and improved RS content up to 18.06% in most legumes. The starch and RS samples were then supplemented at 5% (w/v) in nutrient broth to investigate their prebiotic effect on fish gastrointestinal lactic acid bacteria. Enzyme pre-treatment improved the growth of W. cibaria, L. garvieae and E. gilvus by up to 43.9% for most legumes tested. Red lentil and adzuki bean enzyme-RS showed highest prebiotic potential and was applied in the zebrafish growth trial, while only red lentil was used in the Asian sea bass growth trial. Supplementation of diets with RS from legumes provided no significant difference in the growth and performance parameters measured in both zebrafish and Asian sea bass when supplemented at 2.5% and fed for five and six weeks respectively. Further studies involving analysis of immune parameters is necessary to identify prebiotic potential on targeted fish. Nevertheless, this study contributed to promote future work in using underutilised legumes as prebiotic source to improve the fish health under commercial conditions of rearing.

Fusarium head blight pathogens contribute to ear disease in cereals globally, causing yield losses, decreased grain quality, and mycotoxin accumulation in infected grain. Wheat is susceptible to head blight disease after ear emergence, during which time ears can also act as hosts for other biological agents, including insects. Grain aphids, Sitobion avenae, colonise ears preferentially over other tissues of wheat plants, and mutual attack of wheat by grain aphids and Fusarium pathogens is likely to occur in the field. Experiments were conducted to elucidate the nature of the interactions that occur between the plant host, aphid pests and Fusarium pathogens. When aphids had also attacked the host plant, exacerbated disease severity was observed for both Fusarium graminearum and F. langsethiae. Of particular interest was the finding of an increase in mycotoxin accumulation in infected grain when there was aphid herbivory of host plants. Transmission of either species by aphids was not consistently observed, although the apparent compatibility of F. langsethiae with aphid vectors was greater than for F. graminearum. F. langsethiae was transmitted by aphids when moved manually from infected host ears to susceptible healthy ears, but transmission by natural movement of both winged and wingless aphids failed to produce disease in new hosts. In contrast, deoxynivalenol-producing F. graminearum induced the production of volatile host chemicals that repelled aphids, and population dynamics of aphids that colonised wheat ears infected with F. graminearum were impacted negatively, as observed by increased mortality and decreased fecundity of aphids from diseased hosts. The role of mycotoxins in the production of host volatiles was assessed by comparing F. graminearum isolates of different chemotypes, including mycotoxin deficient mutants. In contrast to hosts infected with DON-producing F. graminearum, which produced VOCs that repelled aphids, hosts infected with a nivalenol (NIV)-producing F. graminearum isolate produced VOCs that were attractive to aphids. This response was shown to be due to the mycotoxin production of the pathogen, as a transgenic line of the same isolate deficient impaired in trichothecene production produced no such effect. The importance of timing and location of aphid herbivory relative to the infection site on the development and spread of disease was examined. It was observed that the longer the time of aphid colonisation on hosts prior to the arrival of fungal inoculum, the more severe the consequences of disease for host plants in terms of fungal biomass and visual disease severity. Aphid herbivory on host ears led to a greater increase in disease severity and spread than infestation of leaves. Systemically treated plants also became more vulnerable to elevated pathogen colonisation; however local effects were more influential on disease outcome. The current research findings show the value of considering interactions between plant pathogens and insects. These are usually studied separately but occur together in nature and in this case the insect had a major impact on disease development. This opens questions about how aphids improve host suitability which could be answered by transcriptomic approaches. The study has important practical implications because it suggests that by incorporating traits for resistance to aphids, breeding for FHB resistance could be improved in wheat. Furthermore, control of aphid populations prior to and during heading could reduce the risk of mycotoxin contamination of wheat crops.