Yield production was investigated in the winter oilseed rape variety Capricorn by comparing crops grown under standard husbandry conditions in three seasons (1991, 1992 and 1993 harvest years). Also investigated were the effects of the phytotonic imidazole fungicide prochloraz on the physiology of yield production. Prochloraz was applied in autumn, spring and summer in all possible combinations (eight treatments), except in the second season (1992), when the autumn application was omitted. Crop growth and development were studied in detail using stratified sampling in 20 cm layers. Detailed growth analysis between flowering and final harvest was restricted to untreated controls and plots receiving all three prochloraz applications. Solar radiation interception was measured using tube solarimeters arranged to correspond with layers of the profile obtained in sampling. The qualitative pattern of growth and development was the same in all three seasons regardless of variations in environmental conditions, and could be divided into the four distinct but overlapping stages described in previous studies. Potential yield (pod number) was determined at flowering and was almost constant between seasons. It did not limit final yield and can never be fully realised. Final seed yield was dependent upon the amount of solar radiation intercepted in Stage IV (seed development), and was manifested in the extent of pod and seed losses and seed growth during this period. The efficiency of radiation use varied between seasons. The main role of leaves was the development of the reproductive framework, and rapid leaf senescence occurred at flowering, particularly in Stage III (pod development). Losses of potential pods and seeds were continuous from flowering onwards but were severe in Stage III. Pod retention was determined by the availability of assimilates which depended on radiation interception and intra-plant competition for assimilates. Regulation of this was probably under hormonal control. Dry matter production was unaffected by the flower canopy except when radiation levels were unusually low during Stage III. Final yield was not affected by such effects. Seed number per pod is determined genetically, but modified during development by assimilate availability according to position in the canopy and the number of competing pods. Seed growth occurred mainly in Stage IV and depended upon the extent of photosynthesis, largely in pods and branches. Seed yield was independent of growth up to flowering, and no remobilisation of dry matter occurred to support seed-filling. When open canopies were produced, leaf retention (largely at the base of the pod canopy), radiation interception by leaf, and therefore, assimilation by leaf, were all increased. Under such circumstances, assimilate production by leaf at the base of the pod canopy may have contributed up to 20% of the dry matter (seed) produced in Stage IV. Pod and seed retention were improved throughout, but particularly higher in the canopy, because seeds that were growing well were more likely to be retained. Disease development in all treatments was monitored using detailed assessments throughout each season. The main fungicidal effects of prochloraz were on light leaf and pod spot and stem canker. Disease incidence was reduced in all seasons, but severity was reduced only in 1993. However, disease severities were generally very low, and these fungicidal effects probably had little or no effect on yield. Large losses of potential yield were caused by severe sclerotinia infection combined with high temperatures, a high soil moisture deficit, and possibly lodging (1992). Sclerotinia was controlled by iprodione in 1993. Disease data were used to form a model to estimate the expected yield losses caused by sclerotinia infection. Heavy infections of stem canker in 1993 did not seriously affect yield. Prochloraz increased seed yield by up to 16% in 1991 through increased pod numbers largely in the upper and middle regions of the pod canopy. Seed number per pod was increased slightly, largely due to higher retention in lower pods, while 1000-seed weight was not affected. Effects were negative in 1992 and inconclusive in 1993. Prochloraz increased crop growth from March onwards in 1991, and the differences in green area and dry matter components were maintained to final harvest. There was no effect on harvest index. Leaf senescence was delayed by prochloraz so that during Stage IV (seed development), leaf area index in the pod canopy and just below was greater in treated plots, and the proportion of radiation intercepted by leaf was slightly increased. Total radiation interception was increased due to the increased green area index mainly due to increased pod and stem areas in the top and middle of the canopy. Prochloraz delayed crop senescence and therefore reduced the decline in efficiency in late Stage IV. Total assimilate production in Stage IV was increased partly because of continued assimilate production for longer in all organs including retained leaf. This enabled more pods to be supported throughout the canopy. By prolonging assimilatory activity in the organs at the base of the canopy, prochloraz probably modified the pattern of assimilate movement between layers of the canopy. Seed numbers per pod in lower pods and pods higher in the canopy would, therefore, have been maintained. Reasons for the failure of prochloraz to elicit a similar response in 1992 and 1993, and the nature of the phytotonic effect are discussed. The findings are discussed in relation to the development of an oilseed rape ideotype for maximising yield production.

Nitrogen (N) fertiliser is one of the most important agronomic inputs and yet the application recommendations for winter wheat (Triticum aestivum L.) still remain imprecise. This increases costs both to the wheat grower and to the environment. An understanding of the canopy nitrogen requirement (CNR) is required before any improvements in fertiliser recommendations can be made. The CNR is defined here as the minimum amount of N required to produce and maintain a canopy and be efficient in light capture and conversion. This thesis aimed to provide a physiological explanation for this requirement in winter wheat, based on canopy structure and radiation geometry, to test the hypothesis that CNR can be predicted from canopy architecture. Variation in CNR was predicted from canopy architecture using data from the literature and a series of principles developed here. The prediction for the photosynthetic N requirement of the laminae and leaf sheath was based on the light distribution, modelled by a form of Beer's Law, and maximising N use efficiency (NUE). The structural N in the true stem was predicted from stem dry weight, stem area and the assumption that 0.3% of stem dry weight is structural N. Field experiments in 1997/8 and 1998/9 were designed to test these predictions by creating a wide range of canopy architectures through three seed rates (20, 320 and 640 seeds m-2) and two varieties (Soissons and Spark). In the 1998/9 experiment there was also a low fertiliser N treatment to reduce the amount of luxury N uptake. The CNR of any particular treatment was stable with canopy development and increased canopy size through depth and was an average of 2.2 g m-2; lower than the original proposed CNR of 3.0 g m-2. The CNR of the low seed rate canopy was also greater than the conventional seed rate and Soissons unexpectedly had a greater CNR than Spark. The results confirmed that the green area, light extinction coefficient (k) and incident light could explain the light flux and its distribution through the canopy. However, in the low seed rate and early growth, Beer's Law appeared not to hold because full ground cover was not achieved. Leaf N requirement decreased linearly with increased canopy size through depth and most canopies distributed N to maximise NUE. The results suggested that of the 50% of total N in the stem, 35% was photosynthetic N in the leaf sheath, 25% was structural in the true stem and the remaining 40% was transport, metabolic, storage and luxury N. The photosynthetic N requirement was overestimated in the prediction indicating that the leaf sheath had a lower N requirement than the lamina. Direct measurements of structural N requirement in the stem could not be made but there was supporting evidence for the relationship with canopy architecture. It is suggested that these principles could be used by growers to predict the CNR from canopy characteristics and by breeders to identify traits that could improve yield. Further detailed analysis of photosynthetic requirements and function of N in the stem would allow the development of a more quantitative prediction scheme, which would be the next step to greater precision in fertiliser recommendations.

The cDNA CM-AATI from melon was expressed as a fusion protein in yeast, Saccharomyces cerevisiae. The protein exhibited alcohol acyl-transferase (AAT) activity, producing ester compounds from a wide range of alcohols and acyl-CoAs. A second cDNA clone, Le-AAT1 was identified by heterologous screening of a tomato fruit library with the melon CM-AAT1 probe. The amino acid sequence of the encoded protein showed some similarities to many proteins using acyl-CoAs as substrates, including CM-AAT1. The Le-AAT1 open reading frame (ORF) consists of 1329 nucleotides, encoding 442 amino acids, while the CM-AATI ORF is 1431 nucleotides in length with a deduced sequence of 476 amino acids. Although the Le-AAT1 showed 43% identity to the CM-AAT1 at the amino acid level, the yeast expressed protein demonstrated AAT activity. On the other hand, a second melon clone, CM-AAT2, encoding a 475 amino acid protein, which is 86% identical to the CM-AAT1 protein, did not show AAT activity. The CM-AAT1 fusion protein was active over pH 6.0 to pH 8.0 in vitro with activity being enhanced by Mg2+, whereas the Le-AAT1 protein performed efficiently at pH between 6.0 and 9.0 with Na+. The activity of the CM-AAT1 protein probably requires posttranslational modifications since the protein expressed in Escherichia coli was inactive. Northern analysis of RNA from a range of tissues including developing fruit showed that the melon CM-AAT1 and the tomato Le-AAT1 are fruit ripening specific genes. The endogenous CM-AAT1 mRNA was ethylene inducible and the expression dramatically reduced in transgenic low ethylene melon. The expression of Le-AAT1 mRNA was also enhanced by exogenous ethylene, but the levels were still high in low ethylene tomatoes. The ADH2 protein, which can transform aldehydes to alcohols, was found to be expressed in various organs of tomato and highly expressed at the late ripening stages. Exogenous ethylene could not induce high accumulation of the ADH2 mRNA. Tomato plants were transformed with gene constructs containing the CM-AATI sense and partial Le-AATI antisense cDNAs with either CaMV 35S promoter or tomato ACO I promoter. The production of all selected volatile compounds greatly increased during tomato fruit ripening. Although ester volatiles were rarely generated at the start of fruit development, they were produced in significant amounts as ripening proceeded, but were still low, compared to other volatiles. There was, however, no statistical difference of the ester concentrations in fruit between control and transgenic tomatoes.

Lethal disease (LD), a phytoplasma lethal yellowing-type disease of coconut palms, is the major threat to coconut cultivation in the coastal areas of Tanzania. Two molecular approaches have been developed for early and accurate disease diagnosis. Random fragments of LD phytoplasma DNA were generated as probes for pathogen detection. LD DNA extracted from infected coconut tissue was randomly fragmented and cloned into pUC 18. Selected recombinants were labelled with DIG-dUTP and used as probes in dot-hybridizations with total DNA from LD infected palms. The probes hybridized strongly to DNA from infected palms, but there was also a significant level of background hybridization to DNA from healthy palms. The second technique used oligonucleotide primers for conserved regions of the 16S rRNA gene and variable spacer regions between 16S and 23S rRNA genes in the polymerase chain reaction (PCR). Amplification of phytoplasma rDNA was primed from LD-infected palms in Tanzania, Kenya and Mozambique, and no amplification products were obtained from healthy coconut tissue. By use of these techniques infection could be reliably detected in the spear leaves and root tips of affected palms thereby avoiding destructive palm sampling. The pathogen was found in all meristematic tissues with highest concentrations of phytoplasmas in the petioles of young unemerged leaves, the area below the growing point and the root tips in palms with moderately advanced diseases symptoms. Root tips proved reliable for sampling when compared to spears, and are now recommendet do be sampled together with the spears in routine, non-destructive sampling. Phytoplasmas could be detected in symptomless palms one month before the onset of disease symptoms by use of DNA probes and two months before by PCR, when spear leaves were sampled monthly from 180 randomly selected palms for a year. Of the 24 palms which subsequently developed disease LD was detectable in 25% prior to the onset of disease and in 46% at the time disease symptoms were visible. In 29% of these palms, phytoplasmas were not detected at all. No phytoplasmas were detected in any of the palms which remained healthy. The genetic relatedness of the LD phytoplasma to twelve different non-coconut infecting phytoplasmas, two spiroplasmas and phytoplasmas causing LYD in Kenya, Mozambique, Ghana, Florida and Jamaica were investigated. The LD DNA probe did not hybridize to any of the non-coconut infecting phytoplasmas and spiroplasmas. However, the probes detected a strong genetic relationship to all the LYD phytoplasmas. By use of PCR analyses, the phytoplasma causing LYD in Kenya was not found to differ from LD, but the pathogen causing LYD in Mozambique was found to be different. This appeared to be more closely related to the LYD phytoplasmas in West Africa. Studies on auchenorrhinchous insects in LD infected coconut fields revealed a strong relationship between seasons and insect flight into the fields. They also showed that local environmental conditions have a strong influence on vector populations, and may be indirectly responsible for the differences in disease incidence observed in different regions of the country. The flight pattern of auchenorynchous insects in general and of Diartrombus mkurangai in particular , coincided with the pattern of disease spread implying that this species is the most probable vector of LD. A good correlation obtained when the disease incidence data was regressed on the numbers of Diastrombus mkurangai and Meenoplus spp, but not on the total number of trapped auchenorynchous insects provided additional evidence or implicating these species as vectors of LD. More than 5000 individual insects were analysed by PCR in attempts to identify the insect vector or vectors for LD. PCR products of the right size were amplified from a few individuals of the species Diastrombus mkurangai and Meenoplus spp, and were shown to be LD phytoplasma by RFLP analysis. The techniques have provided a quicker and more reliable means of detecting LD phytoplasmas in coconut tissues and in putative insect vectors than the conventional methods. Possible improvements on the techniques are suggested and the prospects of utilising them to find a sustainable method of disease control discussed.

The productivity of two spatial arrangements of a perennial pigeonpea/groundnut agroforestry system was examined in relation to the capture and use of light and water and alterations in microclimatic conditions. Line planted (5.4 m alleys) and dispersed arrangements (1.8 x 1.2 m spacing) of pigeonpea were compared, using populations of 0.5 plants m2 for pigeonpea and 33 plants m2 (0.3 x 0.1 m spacing) for groundnut in both treatments. Sole pigeonpea and groundnut treatments were included for comparison. The experiment was conducted between July 1989 and March 1991 on a 0.6 ha plot of Alfisol at ICRISAT Center, Andhra Pradesh, India, using a randomised block design with four replications. The first groundnut harvest took place in October 1989, while pigeonpea was harvested for grain and fodder in January 1990, and was cut to a height of 0.5 m during the 1990 dry season and again in August 1990 after a second groundnut crop was sown. The second groundnut harvest took place in November 1990 and the final pigeonpea grain harvest was in January 1991. Light interception, soil and leaf temperatures and saturation deficit were continuously monitored in all treatments and at various distances from the pigeonpea in the line and dispersed treatments, whilst windspeed was monitored at a single location in each treatment. Regular destructive samples of groundnut were used to establish effects on growth and development and the results were considered in relation to the concurrent physical measurements to determine the environmental factors influencing productivity. In order to establish a water balance, rainfall records were maintained, runoff plots were installed and soil moisture content was measured regularly throughout the drying cycle. Transpiration by pigeonpea was monitored using a heat balance technique, while transpiration by groundnut and soil surface evaporation were estimated from micrometeorological data. As pigeonpea is initially slow growing, there was little reduction in groundnut yield in either the line or dispersed treatments in 1989 and there was a slight intercrop advantage in overall biomass production when expressed in the terms of the land equivalent ratios. In 1990, groundnut pod yield was reduced by 20 and 44 % in the line and dispersed treatments relative to the sole crop, despite substantial increases in the light conversion coefficient for the shaded groundnut. The lower pod yield resulted from the delayed onset of pod initiation and a slower rate of development, and was mainly due the effects of shading by the pigeonpea canopy, although mild water stress may have been a minor contributory factor. The small reductions in saturation deficit and soil and leaf temperatures experienced by the shaded groundnut had a negligible effect on growth and development. There was a considerable increase in overall biomass production in the line and dispersed treatments as compared with 1989 due to rapid pigeonpea growth, which reflected an increase in overall resource use rather than in the light conversion coefficient or water use ratios of the systems. The influence of spatial arrangement on the growth and productivity of pigeonpea became apparent after the 1990 dry season. Biomass production by pigeonpea in the dispersed treatment was approximately double that of the line planting between August 1990 and January 1991. This was entirely due to increased transpiration by the dispersed pigeonpea as a result of greater utilisation of stored soil moisture and reduced losses by surface evaporation and deep drainage. There was no difference in the water use ratio. To examine further the mechanisms responsible for the differences in productivity and water use by the line and dispersed pigeonpea, trench profile methodology was used to examine the root systems in December 1990. The root system of the dispersed pigeonpea was distributed over the entire 2.0 m depth x 2.7 m width exposed soil profile, whilst that of the line arrangement occupied no more than 50 % of the same area. The results of this work are discussed in relation to previous studies of resource use and productivity in intercropping and agroforestry systems, and possible applications and future developments are considered. Finally, the major physical and socioeconomic factors determining the potential of perennial pigeonpea/groundnut agroforestry systems for adoption by farmers in semi-arid India are discussed.

Winter wheat (Triticum aestivum L.) is the most extensive arable crop in the UK grown on about 2M ha p.a. There is a need to identify traits to ameliorate yield losses to drought which are on average about 15% per year. These losses will be exacerbated with predicted climate change. The overall objectives of the present study were to investigate the physiological and genetic bases of water-use efficiency (ratio of above-ground dry matter production to evapotranspiration; WUE) in winter wheat grown in UK conditions and to quantify relationships between WUE and yield performance under drought. The present study used a doubled haploid (DH) population of 33 lines derived from a cross between Beaver and Soissons, known from previous work to contrast for WUE. Two glasshouse experiments (2002/3 and 2003/4) and two field experiments (one at ADAS Gleadthorpe, Nottinghamshire in 2002/3 and the other at Sutton Bonington, University of Nottingham in 2004/5) were conducted. In the glasshouse experiments, two irrigation treatments (with and without irrigation) were applied to four genotypes (two parents and two DH lines), and in the field two irrigation treatments (rainfed and fully irrigated) were applied to the two parents and the 33 DH lines. A range of physiological traits was measured, including developmental stages, carbon isotope discrimination (Δ13C), leaf gas-exchange variables, green areas and biomass at sequential samplings, and these traits were related to grain yield. Transpiration efficiency (ratio of above-ground dry matter production to transpiration; TE) was assessed using the established inverse relationship between TE and Δ13c. In the glasshouse, WUE measured as the regression slope of dry matter on water use, did not differ amongst genotypes in 2003, but did in 2004. Soissons showed higher WUE than other genotypes under irrigation, and also higher WUE than Beaver under drought. For measurements of TE according to Δ13. Soissons and line 134G showed lower Δ13C values (higher TE) than line 134E and Beaver (P<0.05) in 2004 under both irrigation and drought. Soissons and line 134G showed consistently higher TE on account of lower stomatal conductance (gs ) and sub-stomatal C02 concentration (C) values. The early developing Soissons and line 134G exhibited greater flag-leaf green area persistence under drought than the late developing Beaver. Beaver tended to use more water than Soissons under both irrigation and drought, but reductions in water use under drought were similar amongst genotypes. Lower seasonal water use for Soissons than Beaver was associated with a smaller root system. There was a tendency for dry matter of Beaver to be more depressed under drought than Soissons in both the years. Overall, it was not possible to detect significant differences in biomass responses to drought amongst the genotypes, but there were consistent genetic differences in WUE and TE observed under both irrigated and droughted conditions. In the field experiments, the onset of drought coincided broadly with anthesis. The average grain yield losses under drought were 0.5 t ha-1 in 2003 and L6 t ha-1 in 2005. Averaging across site/seasons, Δ13C correlated positively with grain yield amongst the 35 genotypes under irrigation (r--0.35; P<0.05) and under drought (r--0.54; P<0.01), indicating a negative trade off between TE and yield. A 13C decreased under drought and a higher TE was associated with a reduction in average flag-leaf gs, measured from flag leaf emergence to anthesis + 4weeks. Stomatal conductance was measured for eight of the 33 DH lines including the parents, and there was a trend for lower Δ13C (higher TE) to be associated with lower gs, The genetic differences in gs, were generally associated with corresponding decreases in Ci and net photosynthetic rate (A). Therefore results suggested that the negative relationship between TE, as indicated by Δ13C and yield was associated with corresponding reductions in seasonal water use. There was a nonsignificant irrigation x genotype interaction at Gleadthorpe in 2003 and Sutton Bonington in 2005 for Δ13C indicating that this trait was of high heritability. There was an irrigation x genotype interaction for grain yield (P<0.05). A small number of genotypes showed higher yield associated with low Δ13C and these outlier lines could potentially be identified for breaking the negative linkage between yield and delta. In summary, WUE was negatively correlated with yield under drought in this population; and season-long water use appeared to be the most important component affecting yield levels under drought. It is suggested that selecting genotypes indirectly for high Δ13C (low WUE) may be a strategy to improve grain yield under drought. In the quantitative genetic analysis, the putative QTLs identified for target physiological traits were generally different at Gleadthorpe in 2003 and Sutton Bonington in 2005. The most confident putative QTLs for Δ13C were mapped on chromosomes 3B (LOD=2.32) and 2D (LOD=1.43). The identification of QTLs as potential candidate genes on these chromosomes may be associated directly with WUE in the Beaver x Soissons DH mapping population. The Δ13C QTL on chromosome 3B was detected commonly in both the irrigation environments and the direction of allelic effects was consistent with the parental differences in Δ13C. This QTL may therefore represent a novel gene for optimising WUE. It is suggested that breeders could optimise TE by selection according to a marker for this gene involving further fine-mapping to identify a marker tightly linked to the gene. Such a marker would also provide a target for gene discovery in future work. The results suggest that water use is the most important component of Passioura's yield model for yield improvement under UK conditions. Nevertheless, WUE and harvest index and their responses under drought will also likely play a role in yield improvement through breeding in the UK targeted at drought-prone environments in future years.

This investigation was aimed at determining the impact of environmental stresses such as high temperature, low irradiance and drought on reproductive development in sweet pepper, particularly var. Blue Star. Special attention was given to abscission of the primary and secondary flowers. The role of assimilate accumulation and partitioning and the endogenous growth regulator ethylene in mediating stress effects on flower abscission were investigated. The hypothesis that flower abscission is promoted by these stress factors and that abscission is mediated by increased ethylene production and reduced assimilate partitioning to the flowers was tested. Imposition of a mean daily temperature (26 °C) from the third true leaf stage accelerated the development of the first primary flowers to anthesis when combined with high irradiance (4.9 MJ m-² d-¹). However, abscission was increased by 17 % as compared to lower temperature treatments at the same irradiance. The combination of high temperature and low irradiance (2.4 MJ m-² d-¹) induced complete abscission of the primary flowers. Although flower abscission was reduced at the lowest temperature examined (14 °C), development of the primary flowers to anthesis was slower than at higher temperatures. Both varieties, Blue Star and Bell Boy, were able to grow over a wide range of temperatures, as indicated by the large difference (c. 35 °C) between the base and maximum temperatures for growth indicated by a germination trial. In Blue Star, the base (Tb), optimum (To) and maximum (Tm) temperatures were 6.0, 27.5 and 41.5 °C respectively, whereas in Bell Boy, the corresponding values were 8.5, 23.0 and 44.0 °C. Severe water stress imposed progressively after the appearance of the first flower bud promoted the initial development of the primary, but not the secondary flowers to anthesis, but induced early and increased abscission of both primary and secondary flowers shortly afterwards. The high percentage abscission of the primary flowers was partially offset by the lower abscission of secondary flowers. Percentage abscission increased as the severity and duration of water stress increased. However, short exposures to stress did not reduce abscission, or advance anthesis. A more advanced stage of flower development (4.0 mm diameter) proved more susceptible to early abscission than younger flower buds (1.0 mm) when exposed to severe stress. Temporary osmotic adjustment occurred soon after the imposition of water stress, during which osmotic potential decreased sharply from -1.15 to -1.80 MPa, and noticeable reductions in turgor were observed in all treatments between 11 - 22 d after the imposition of stress. Although water stress reduced vegetative growth under low irradiance, complete flower abscission occurred after anthesis. The advancement of anthesis in stressed plants was associated with a decrease in dry matter accumulation in the leaves and stems. However, at the onset of flower abscission, assimilate accumulation and partitioning were not significantly affected by water stress, and flower abscission was not directly related to any reduction in assimilate production or its distribution within the shoot. Instead, prior to flower abscission in severely stressed plants, ethylene evolution in the flowers increased by 8-fold as compared to unstressed plants, and by 40-fold relative to severely stressed plants measured just before anthesis. The application of the ethylene releasing substance, 2 chloroethylphosphonic acid (CEPA), mimicked the effects of severe water stress, as reflected by a surge in ethylene evolution prior to abscission, followed by increased bud abscission. Sweet pepper flowers were also capable of forming abscission zones at the base of their pedicels in response to elevated ethylene production, whilst mature leaves were apparently incapable of this response. Foliar application of silver thiosulphate (STS) to water stressed plants and STS pre-treatment of plants subsequently sprayed with CEPA blocked the action of elevated ethylene resulting from severe stress or CEPA application in inducing flower abscission.

Increases of temperature in the range from 8 to 18°C in vivo, significantly enhanced the dry weights of lateral rhizomes, roots and shoots. At the higher temperatures dry weight production was often seen to decrease. Decreases in irradiance from 100 to 50 per cent in vivo, produced significant decreases in the dry weights of lateral rhizomes, roots and shoots. In contrast, the numbers of lateral rhizomes, tubers and shoots were largely unaffected by temperature and irradiance treatments. Day length treatments of 8 to 16 hours light in a 24 hour period in vivo produced few significant changes in either the dry weights or numbers of plant parts produced. However, day length had a strong influence over the time of flowering. For maximum rhizome production a temperature of between 13 and 18°C, a high irradiance and a short day length were required. Increases of temperature in the range 8 to 18°C in vitro, caused significant increases in the number of lateral rhizomes and shoots produced. At the highest temperature the numbers produced often decreased. The number of roots produced was unaffected by temperature. Decreases in irradiance from 100 to 25 per cent and increases in day length from 8 to 20 hours light in a 24 hour period, produced no significant changes in the number of lateral rhizomes, roots or shoots produced in vitro. Low irradiance, however, caused etiolation of the shoots. For a good multiplication rate the requirements for the culture environment were a temperature of 15°C, an irradiance of 5 Win- 2 with a day length of 8 hours of light in a 24 hour period. The presence or absence of tubers and damage suffered by `splits' prior to planting were found to be important factors in the establishment of plants in vivo. Subculture of rhizome explants without aerial shoot or rhizome apices and of rhizome explants divided into single internodes with or without aerial shoots, enhanced the rhizome multiplication rate. Addition of the plant growth regulators triiodobenzoic acid, thidiazuron, α-naphthaleneacetic acid, gibberellic acid and paclobutrazol to culture media, with and without BAP, caused no significant changes in the numbers of lateral rhizomes, shoots or roots produced. However, paclobutrazol produced changes in explant morphology, i.e. shoot size was reduced and the diameter of roots was increased.

The aim of this research was to widen the knowledge of the physicochemical properties of cassava starch and flour and to understand the factors which influence their functional characteristics, including both genetic and environmental effects as well as processing procedures. A range of chemical and physical techniques which included the Brabender viscoamylograph, Bohlin CS rheometer, Brabender farinograph, WAXS, GPC, SEHPLC and Coulter counter have been used to examine the structural and behavioural characteristics of both cassava starch and flour. The results suggested that the functional behaviour of native cassava starches of different origins varies widely and appeared to be associated with molecular structure and the architecture of the starch granule. The viscosity and the mechanical properties of the pastes produced by gelatinization were determined by the degree of swelling and the amount and proportion of amylose and amylopectin in the solvent phase of the pastes. The amylopectin was present in the solvent phase in substantial quantities which varied between 37 and 57% of the total starch solubilized. In native cassava starches, the amylose appeared to have a high molecular weight (M, 19 x 105 - 11 x 105 ). The constituent chains of the amylopectin molecule did not vary in length with cassava starches of different origins, but their relative population did which was reflected in minor differences in the chromatographic profiles. Starch granules containing long chain amyloses and amylopectin with a high degree of branching were found to release reduced amounts of molecules into the liquid phase of the pastes, and vice versa Where the pastes contained a high proportion of amylopectin and long amylose molecules the resultant gel was surprisingly weak. Cassava starch processed to produce "sour" starch, or fermented, and sun dried starch, was found to have suffered degradation to an extent where 77-86 % of the starch was solubilized during aqueous heating. The extent of the degradation was influenced by the cassava cultivar. The "sour" starch proved superior to unfermented and fermented, oven dried starches in the production of baked baked products with an expanded texture. Starch extracted from cassava roots which had been stored for a short period, during which physiological deteriorative processes could have occurred, was found to show a slight reduction in the pasting viscosity which was not related to granular or molecular size or organization. Rural, factory-extracted starch was found to have a reduced paste viscosity as a consequence of fermentation and contamination with peel residues from the roots. Cassava flour properties were influenced by the conditions of preparation. Drying temperature, milling procedure and particle size could be selected and controlled to give cassava flours of the desired functional properties.

My topic is the genesis of the English landscape garden 1720-1750. This was developed in Britain in the first half of the eighteenth century and has been called "emblematic or learned", since the visitor was expected to decipher its various meanings. These were often communicated through buildings, sculptures and inscriptions, and cumulatively conveyed through the sequences in which these features were arranged. While historians have studied the iconography of some of those gardens (notably Stowe) in depth, there are areas which, though acknowledged, have yet to be dealt with thoroughly. These include the well-known "Chinese" connection, the details of the gardens' political status, the significance of the Venetian aspect of the Palladian revival, and the role of Freemasonry and masonic ideas. In this dissertation my aim has been to explore these various aspects showing how, if considered all together, they can help us to better understand the different meanings of the early landscape garden. In the introduction I give a description of the early English landscape gardens. In the first part I discuss the importance of the Chinese gardens for the origins of the "idea of irregularity" in the new style of garden. Then in the second part I go on to investigate the eighteenth century political background and its connections with the architecture of the early landscape garden discussing the influence that the surviving myth of Venice had on Neo-Palladianism. Finally, I examine whether the garden contained buildings that could reflect masonic moral and architectural concepts.