This research is concerned with the contribution which farmer participation, as a complementary approach to agricultural research in Brazil, can make to the Improvement of disadvantaged farmers socioeconomic conditions through the solution of their technological problems. This notion is embodied in the concepts of Farming Systems Research and Farmer Participatory Research, which provide the broad theoretical framework within which this investigation was developed. The context in which the research was carried out was Brazilian sugar cane growing regions, with a specific focus on the practice of farmer participation within the Three Year' Plan for Diffusion of Technology for Sugar Cane Agro-industry's Resource-poor Farmers (Plano Trienal). Material for this investigation derives from two sources: direct involvement since the pilot project original phase of the Plano Trienal over a period of six years and a period of fieldwork undertaken in 1988. During the latter, data were collected by means of questionnaires, interviews, participant observation and Informal discussions in the States of Sao Paulo, Rio de Janeiro, Minas Gerais, Espirito Santo, Pernambuco, Paraiba and Rio Grande do Norte. The dynamics of sugar cane agriculture is analysed within the overall sugar cane agro-industry as a particular sector of Brazilian agriculture. The concepts of Farming Systems Research and Farming Participatory Research are then set within this general frame of reference. Subsequently, the policies advocated by research and extension services is situated within the wider context of the Brazilian sugar cane agro-industry. Specific attention is then given to the failure of 'conservative modernisation' policies adopted by those services. Within this broad framework the formation and development of the Plano Trienal is described and analysed. The performance of the Plan's selected projects is then investigated through a comparative study, with particular attention given to the types of approaches employed, both, participatory and persuasive. In this perspective, combined statistical and qualitative methods are employed, based on variables (such as technology, approach, farm, farmer and technician) with specific reference to four economic indicators: productivity, assets, adoption and technological problems. Finally, the role of Farmer Participation is critically analysed referring to Farmer Participatory Research as a crucial component of the agricultural research process. The research findings point to the central importance of farmer's indigenous knowledge and scientific knowledge based upon 'mutual respect', and grounded in experience, for the processes of participatory research. In these processes, the relationship established between farmer and technician was found to be a fundamental aspect of research practice in which great weight is placed upon the farmer's role not as an object but as the 'subject' of agricultural research. This research demonstrates that the projects which embraced this approach achieved a higher level of technology adoption, a greater number of technological solutions and a greater increase in productivity and farmers' assets. The main policy implication of the thesis is that farmer participation, as a complementary approach to agricultural research methods, can contribute significantly to modifying the socio-economic situation of disadvantaged farmers.

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Within-field variation in sugar beet yield and quality was investigated in three commercial sugar beet fields in the east of England to identify the main associated variables and to examine the possibility of predicting yield early in the season with a view to spatially variable management of sugar beet crops. Irregular grid sampling with some purposively-located nested samples was applied. It revealed the spatial variability in each sugar beet field efficiently. In geostatistical analyses, most variograms were isotropic with moderate to strong spatial dependency indicating a significant spatial variation in sugar beet yield and associated growth and environmental variables in all directions within each field. The Kriged maps showed spatial patterns of yield variability within each field and visual association with the maps of other variables. This was confirmed by redundancy analyses and Pearson correlation coefficients. The main variables associated with yield variability were soil type, organic matter, soil moisture, weed density and canopy temperature. Kriged maps of final yield variability were strongly related to that in crop canopy cover, LAI and intercepted solar radiation early in the growing season, and the yield maps of previous crops. Therefore, yield maps of previous crops together with early assessment of sugar beet growth may make an early prediction of within-field variability in sugar beet yield possible. The Broom’s Barn sugar beet model failed to account for the spatial variability in sugar yield, but the simulation was greatly improved when corrected for early canopy development cover and when the simulated yield was adjusted for weeds and plant population. Further research to optimize inputs to maximise sugar yield should target the irrigation and fertilizing of areas within fields with low canopy cover early in the season.

Cassava is the sixth most important food crop in the world, where it is the staple food for over 500 million people. Its ability to grow on marginal soil conditions and under minimal care makes cassava a vital ‘food security’ crop for resource-poor farmers. However, cassava production is constrained by post-harvest physiological deterioration (PPD), a storage root disorder characterised by vascular streaking and discolouration of parenchymal tissue. PPD, which renders the roots unpalatable and unmarketable, leads to significant yield loss in global cassava production. The cause of PPD is not yet fully understood but accumulation of reactive oxygen species (ROS) has been observed in the harvested storage root. It is hypothesised that the ROS, which is triggered by wounding during harvesting, is not modulated due to deficiencies in the ROS-detoxifying system in cassava roots, causing oxidative stress to occur, which then leads to symptom formation. To investigate this, transgenic cassavas containing five separate anti-oxidant genes were studied– superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), gamma glutamyl cysteine synthetase (GCS) and galacturonic acid reductase (GAR). Each gene was controlled by a root-specific promoter, Patatin, which is also wound-inducible. A high percentage of single-insert lines were recovered, which retained the outward phenotype of WT cassava. While this enabled comparative PPD assessment between the transgenics and the WT, this was complicated by the challenge of reproducibly measuring PPD in greenhouse-grown plants. Therefore, a reliable assay to measure PPD in greenhouse-grown samples was developed and a robust method to assess the symptoms with high confidence was devised. Scopoletin, a fluorescent compound was initially tested as an alternative PPD marker but was dismissed as it did not correlate well with PPD symptom development. Overexpression of anti-oxidant genes was observed in selected lines – between 4- to 5-fold increase of relative transcriptional level was achieved in fresh roots and up to 20-fold was achieved in transgenic roots that had been harvested after 24 hours. However, as the increase did not alter the activity of anti-oxidant enzymes, the transgenic cassava plants generally exhibited similar levels of tolerance to oxidative stress and PPD as the WT plants. This result may be partly due to the difficulty of producing sufficient numbers of replicates for analysis, the behaviour of the Patatin promoter in cassava, and the complexity of anti-oxidant responses. Hence, while this thesis has clarified aspects of the PPD response in cassava and the role of anti-oxidant genes in it, it has not been able to identify definitive means to control the problem through altering the expression of individual genes.

No description available.

Cassava is a staple crop for over 500 million people worldwide. Production of cassava is affected by several constraints, including viral diseases such as cassava brown streak disease (CBSD), caused by the ipomoviruses Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). CBSD is present throughout cassava growing regions in Africa and symptoms include streaking, chlorosis, dieback and tuber necrosis, leading to crop losses of up to 70%. An increased genetic and molecular understanding of the viruses that cause CBSD is essential for management of this disease. In this thesis, five strategies were evaluated in an attempt to generate infectious clones of CBSV to facilitate further understanding of this virus: fusion PCR, cloning the viral genome in a bacterial artificial chromosome (BAC) in E. coli, the use of E. coli strains developed for unstable clones, intron insertion using homologous recombination in yeast and in vitro ligation. It was determined to be not possible to construct a full-length CBSV clone in E. coli when the cylindrical inclusion (CI) gene was intact, likely due to its toxicity in E. coli leading to instability. Use of an in vitro ligation technique successfully created a cDNA infectious clone of CBSV. In this process, two segments of the genome were generated in separate plasmids and then assembled by in vitro ligation before in vitro transcription. Typical infection symptoms were observed when Nicotiana benthamiana and N clevelandii were inoculated with the infectious transcripts. Following the construction of infectious clones, functional genomic studies were possible. The HAMI gene, unique to CBSV and UCBSV in the Jpomovirus genus, was chosen as the target for functional analysis. The HAMl gene has homology with HAM I in the yeast Saccharomyces cerevisiae which is a nucleoside triphosphate pyrophosphatase (NTPase) that hydrolyses non-canonical nucleoside triphosphates (NTPs) and prevents their incorporation into nucleic acids to avoid unfavourable mis-match mutations. A bioinformatk analysis of HAMI was conducted, a 5-Fluorouracil resistance assay was performed and knockout constructs of the HAMl gene were generated to determine whether HAM I from CBSV and UCBSV has similar functionality to the HAMl in yeast. The multiple sequence analysis revealed that the HAMI from CBSV and UCBSV contains the "signature" motif(SHR) for ITPase family could therefore be expected to have a similar function to other ITPases. However, the CBSV and UCBSV HAMI genes did not confer resistance in S. cerevisiae to 5-Fluorouracil, as shown with the S. cerevisiae HAMI homologue and the UCBSV HAMI-knockout infectious clones were unable to establish infections in N benthamiana and N clevelandii. This suggests that HAMl may be required for infection, rather than function as a NTPase. The construction of the CBSV infectious clone in this thesis, and functional analysis of this virus, will assist in further research conducted on this important pathogen to facilitate management of CBSD and maintain yield of the important root crop, cassava.

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Cassava brown streak disease (CBSD) threatens cassava production in eastern and southern African countries. Diagnostic protocols currently available for the causal agents of CBSD, Cassava brown streak virus (CBSV) and Cassava brown streak Uganda virus (CBSUV), were unreliable but were urgently needed. In this study, sampling procedures and diagnostic protocols were developed for accurate and reliable detection of both CBSV and CBSUV. The cetyltrimethylammonium bromide (CTAB) method of RNA extraction was optimized for sample preparation from infected cassava plants and compared with the commercial kit RNeasy (Qiagen) for sensitivity and reproducibility. Results showed that both protocols were reliable but CTAB was more cost-effective and ideal for resource-poor laboratories. Mixed infections of cassava mosaic begomoviruses (CMBs) that cause cassava mosaic disease (CMD), CBSV and CBSUV have become more common with the recent spread of CBSD at mid-altitudes. A multiplex PCR for the simultaneous detection of viruses that cause both diseases, the first of its kind for cassava, was therefore developed to detect CBSV and CBSUV along with the three commonly occurring CMBs (African cassava mosaic virus (ACMV)), East African cassava mosaic virus (EACMV), and East African cassava mosaic virus-Uganda (EACMVUG) in eastern Africa. Similarly, a duplex PCR was developed for the simultaneous detection of CBSV and CBSUV, both viruses being detected in field-collected samples from Tanzania and Kenya. The genetic diversity of more than 40 CBSD isolates from Kenya, Tanzania, Uganda, and Mozambique was further examined by sequencing the coat protein (CP) gene and partial HAM1 gene sequences. The phylogenetic tree clustered the CBSD isolates into two groups reflecting the two virus species causing CBSD. In this study, various strategies were carried out for generating infectious clones of CBSV; gateway cloning, in vivo and in vitro transcription methods, and amplification of the viral genome in three fragments. Although 3 overlapping CBSV fragments were successfully cloned, the presence of an unexpected mutation at one of the cloning sites unfortunately did not allow reassembling of the fragments to construct the full-length cDNA.