No description available.

No description available.

No description available.

Human-induced land use changes, including deforestation, agricultural encroachment and urbanisation, have caused widespread change in the global distribution of organisms and caused considerable declines in biodiversity through loss of habitat. Oil palm is one of the most rapidly expanding crops in Southeast Asia, but the impact of this crop on mosquito distribution, behaviour and exposure potential has been poorly explored. Understanding these factors is essential for developing, optimising and evaluating novel control measures aimed at reducing disease-transmission. This thesis explored the effect of land use change along an anthropogenic disturbance gradient (primary forest, disturbed forest, highly disturbed forest, oil palm plantations and rural housing estates) in Sabah, Malaysia. The community composition of anthropogenic mosquitoes was separated across land use, with the biggest difference seen between primary forest and oil palm plantations. This was largely driven by medically important mosquitoes attracted to oil palm plantations. Differences in community composition were also seen in areas of rural housing in comparison to primary and disturbed forest sites, due to a high presence of the dengue vector, Stegomyia albopicta, in housing areas. A higher abundance of anopheline vectors were found landing on humans in the disturbed forest and oil palm plantations then primary forest. This thesis found no difference between highly disturbed forest and oil palm plantation sites. This thesis also investigated the host-seeking behaviour of simian malaria vectors, by carrying out human landing catches at ground and canopy level across land use. Results demonstrated the potential ability of one of the vectors, Anopheles balabacensis, to transmit the simian malaria (Plasmodium knowlesi) between canopy-dwelling simian hosts and ground-dwelling humans, and that anthropogenic disturbance increases the abundance of the disease vector. Finally, this thesis investigated the use of different marking methods and the need for an improved dispersal experiment to be carried out.

No description available.

No description available.

Crude extracts of the seed kernels of the neem tree (Azadirachta indica) are widely used as plant protection products. The active ingredient (a.i.) of these extracts is azadirachtin A (aza A). aza A is a phytochemical (botanical) complex secondary metabolite which, with it is multiple toxic effects on insects, protects the plant against predation. Aza A is present in only low concentration in neem oil, but makes up 20-50% in the NSKEs extracted by polar solvents from the kernels. However, when used as foliar sprays it is rapidly destroyed by sunlight, and might be more effective if it is used systemically. Therefore the aim of the project was to extend previous work and to prepare a pelleted version of the main commercially-available neem-seed kernel extract, NeemAzal®-Technical (NAT) produced by Trifolio GmbH, in preparation for the expected registration of the product in the UK in 2011. It was first necessary to purify a quantity of aza A for quantification of the a.i. pelleted material and in soil and plants in the rest of the project. In achieving high purity (over 98%) aza A, reverse phase chromatographic methods were used, and mass spectrometery was used to confirm purity and identification. A final quantity of 6.2 mg of azadirachtin A was obtained from 4 gm of NAT, a yield of 0.15%. If aza A and the other neem terpenoids are to be used to plant protection, they must have a low phytotoxicity. Effect of NAT on the germination and its ensuing seedling development of two commercially important crops, sugar beet and cabbage was examined. NAT did have an inhibitory effect on seedling growth at 10-3 M aza A. In order to explore the inhibitory affect of aza A, the second part of the chapter was to examine effect of aza A on mitosis of onion root tips. The limonoids in concentration of 10-3 M adversely affected the mitotic activity of onion root tip cells. This could be failure of microtubules polymerisation into microtubules, or some other biochemical effect. From the findings in this part of the project, it can be concluded that only at a concentration of 10-3 M is aza A toxic to plant young seedlings, but in practice this is unlikely to be a significant problem. The first part of Chapter 4 of the project was to lay the foundations for the behaviour of aza A in soil environment in both powder form and in 2 types of granular formulations. The half-life of azadirachtin in soil from this work was found to be 1.6 days which is consistent with the previous reports. This short half-life of aza A may be problematic in use as a PPP. The short persistence might be overcome by formulating neem materials in granules to achieve environmental stability and biological efficacy of application. The granular formulations used in the project showed controlled release characteristics. The release of azadirachtin into the soil water was in fact delayed by encapsulating it in pellets. Systemic uptake of aza A by roots and subsequent presence in the vascular system of plants was assessed. Aza A was transported and was more stable in the leaf areas of cabbage and sugar beet plants than in the soil, as the half-life was found to be 9 days. The concentration of aza A in the leaf-water was less than 10% of the solution bathing the roots. The final part of the project, the application of the pelleted NSKE to protect cabbage, in both glass house and field conditions, demonstrated that neem products in pelleted formulations could be used as effective, systemically applied PPP to control pests of cabbage. In the field tests, the protective effect of the neem extract could be shown over a period of at least 5 weeks after addition of the pellets to the soil. In conclusion, the short soil half-life of the neem a.i., aza A, in PPP could be overcome by a pelleted formulation, the composition of which can delay release of the a.i. The technology allows protection of crops from soil-borne, as well as foliar sucking and biting pest damage by controlled release into the soil to allow uptake into plant vascular system.

This thesis seeks to quantify the effect of land use change from tropical forest to oil palm plantation on nitrogen biogeochemical cycling in Sabah, Malaysia (Borneo). Nitrogen cycling process rates and indices were examined across four forests and six oil palm plantations during the inter-monsoon and end of wet season in 2010 and 2012 respectively. Firstly, the study establishes a baseline to assess the impact of land use change along a chronosequence of forest succession. Results indicate that forests follow a trajectory of nitrogen recovery and increased “openness” to nitrogen cycling through secondary forest development. Secondly, the spatial and temporal variation of nitrogen cycling within oil palm plantations is assessed. Results show that plantation management practices result in spatial variability in soil nitrogen. Examining process rates revealed an increasing trend of N\(_2\)O emission and decreasing trends of soil organic matter content as plantations matured. However, season and soil type also affected denitrification and N\(_2\)O emission. Finally, a replicated comparison of process rates in forests and plantations on riparian and terra firme soils revealed that plantation establishment significantly altered rates of nitrogen cycling and resulted in greater emissions of N\(_2\)O from \(terra\) \(firme\) plantations.

Oil palm is a dynamic economic crop that provides good income and is a source of dietary energy for the global population by palm oil. However, oil palm has low resistance to basal stem rot (BSR) disease caused by Ganoderma boninense. It is hypothesised that the process of cell wall lignification could serve as the first line of defence in oil palm. Lignification delays the infection progress of G. boninense. This present study evaluated the underlying molecular and biochemical lignin biosynthesis events and the quantification and deposition patterns of lignin in oil palm upon G. boninense infection. In this study, an artificial in planta infection system was used to inoculate one month-old oil palm plantlets with G. boninense (GBLS strain) at three levels of treatments (control, T1; wounded, T2 and infected, T3). Post-infection analyses were conducted at 2 day intervals for a period of 8 days. The analyses included the disease severity index (DSI) and physical properties of the plantlets (height, weight, stem diameter, root length and leaf chlorophyll content), the degree of G. boninense colonisation on plantlets stem tissues, total phenolic content and total amount of G. boninense DNA in planta. The results showed a significant (P < 0.001) reduction in the leaf chlorophyll content (from 32.59 to 12.61 SPAD) and severe deterioration of the internal stem tissues. Escalation of DSI values (from 5.56 to 70.37%), total phenolic contents (from 1.78 to 3.07 mg g-1) and the quantity of G. boninense DNA (from 4.04 to 757.15 mg g-1) in the infected (T3) plantlets on 8 day post-inoculation (DPI) were observed. These differences (P > 0.05) were absent in control (T1) and wounded (T2) plantlets. Colorimetric enzyme assays and quantitative PCR amplifications (qPCR) were carried out to assess the enzyme activities and relative gene expressions of intermediate enzymes (phenylalanine ammonia lyase, PAL; cinnamate 4-hydroxylase, C4H; caffeic acid O-methyltransferase, COMT; cinnamyl alcohol dehydrogenase, CAD) for lignin biosynthesis in oil palm plantlets. Enzyme activities of PAL, C4H and COMT were generally induced in infected plantlets, except for CAD which was reduced in all plantlets throughout the experiment. Meanwhile, relative expression of EgPAL, EgCOMT and EgCAD were up-regulated in infected plantlets by 3 to 6 fold at 2 to 4 DPI as compared to the control plantlets, except for EgC4H which was initially down-regulated, but was induced later at 8 DPI with the highest change recorded of 13.22. A biphasic transient induction pattern of lignin biosynthesis genes was observed in oil palm plantlets upon infection by G. boninense. The lignothioglycolic acid (LTGA) assay, histochemical staining with toluidine blue-O (TBO), Maúle reagent and phloroglucinol-HCl and gas chromatography (GC) equipped with a flame ionisation detector (FID) were used to estimate and detect the total lignin content, lignin deposition patterns and the composition of lignin derivatives such as syringaldehyde and vanillin, respectively. Results showed the infected plantlets scored the highest level of total lignin content at 93.63 TGA g-1 derivatives at 8 DPI. Lignin was mainly deposited on the collenchyma and cuticle layers, as observed via staining with TBO and Maúle reagents, but red colouration from phloroglucinol-HCl, which stained for guaiacyl-lignin was absent in all specimens. Total amounts of syringaldehyde and vanillin increased in infected plantlets at 6 DPI, with higher increment of vanillin (353%) than syringaldehyde (59%) content. From this study, an early induction of lignification in oil palm was confirmed in response to the infection of G. boninense. This resulted in the accumulation and deposition of lignin compounds in the cell walls of oil palm. An increase in lignin content of oil palm was believed to have enhanced its tolerance towards G. boninense infection and delayed the progression of BSR disease, which could be a temporary solution to the BSR problem in oil palm. Further research for an effective cure or prevention is required.

Oil palm is an important crop to the economy of Malaysia and Indonesia. There have been considerable efforts to improve crop quality of crop to meet the growing demands for edible oil in the world. However, the threat of pests and diseases in Malaysian oil palm has increasingly challenged the production of crude palm oil, sometimes to the point of driving plantations to closure and conversion of estate land for commercial development. The most devastating disease in oil palm is basal stem rot (BSR), caused by the root-rot pathogen Ganoderma boninense. The disease has been observed in both young and mature oil palm and in both inland and coastal plantations. Epidemiology of BSR was explained through infection by spores and by mycelium from previously infected oil palm and coconut stands, and the presence of G. boninense in the basal stem and soil surrounding infected palms. The life cycle of G. boninense could extend to years as the fungus can remain as resting structures in palm tissues and as recalcitrant spores spread by wind and rain splash in estates. Shade house trials have been successful in producing artificially infected Ganoderma-oil palm BSR symptoms. However, the current method uses oil palm seedlings of three to 12 months and involves inoculation with G. boninense that has pre-colonised a rubber wood block for one month. This method requires a minimum of six months to observe BSR-like symptoms, a time consuming effort. The aim of this work was to develop an efficient artificial infection assay that uses clonal oil palm plantlets as hosts for BSR disease through the inoculation of G. boninense isolate GBLS. The experiment was set up with treatments of T1: non-treatment control, T2: wounded plant control and T3: wounded and GBLS-infected plants. During the incubation period of 42 days, T3 plants consistently showed significant stunting (5.18% and 13.41% shorter than T1 and T2, respectively) and loss of weight (57.58% and 61.00% lighter than T1 and T2, respectively). The T3 plants also had significantly thinner leaves (38.70% and 37.71% narrower than T1 and T2, respectively) and lower chlorophyll contents (42.95% and 64.88% lower SPAD readings than T1 and T2, respectively). Disease severity on the T3 plants was 100% by 6 weeks, indicating death of oil palms. The quantity of GBLS DNA present in T3 samples was highest at Day 14, corresponding to the active growth phase of the pathogen, while on Day 42, the quantity of DNA increased to 13.58% of Day 14 readings, indicating continuous growth in vivo. The method developed was time-sensitive and reliable for screening oil palm for response during the plant-pathogen interaction. The work examined the hypothesis that G. boninense utilizes lignin degrading enzymes (LDEs) such as laccase, lignin peroxidase (LiP) and manganese-dependent peroxidase (MnP) to breakdown oil palm lignin, causing primary cell, tissue and stem rot. Therefore, the role of laccase was investigated during the interaction in otherwise symptomless oil palm tissues. A small gene fragment (208 bp) of laccase was isolated from total DNA of G. boninense GBLS and sequencing showed it to contain 89% homology to basidiomycete laccase. GBLS reduced the total lignin content of oil palm in T3 plants (48.86% and 53.18% lower than T1 and T2, respectively). However, neither laccase nor MnP enzymes were produced in significantly higher amounts in T3 as compared to T1 and T2, indicating the need to differentiate the presence of plant and fungal laccases. Transcript abundance for GBLS laccase gene using qPCR indicated that laccase was induced during the interaction, with maximum laccase detected on Day 28. However, this did not place laccase as a virulence factor although the presence of higher amounts of laccase towards the end of the experiment corresponds to loss of lignin and plant death. Therefore, laccase and other LDEs need further investigations to be confirmed as virulence factors. This work reports a novel infection assay for G. boninense interaction with oil palm and was the first study to have investigated the role of G. boninense laccases in the devastating BSR disease.