Epsilon toxin (Etx) produced by Clostridium perfringens type D is responsible for a fatal Enterotoxemia (Pulpy Kidney Disease) in economically significant livestock such as sheep and goats. The only practical means of controlling this disease is by immunisation and avoiding the circumstances that are conducive to its occurrence. All currently available Pulpy Kidney Disease vaccines are based on a formalinised toxoid of Clostridium perfringens (Welchii) type D. This is either as an alum-precipitate, oil-emulsion formulation of the whole cell culture or a bacterial culture filtrate (Deepika, 2010). The current vaccine has several drawbacks. First, it is generally accepted that its chemical inactivation with formalin is difficult to standardise. Second, the classical methods of detoxification usually alter the overall protein structure in a random manner. Consequently, the immunogenicity of this type of a vaccine is decreased substantially. Third, there is a narrow range in balancing the detoxification (the strength of formalin commonly used is 1%) and the immunogenicity of the vaccine (Robertson et al. 2011). Alternatives to formalin inactivation have been proposed because of these challenges. These include ectopically expressing the mutated toxoids in other gram-positive microorganisms. Apparently, plants provide a genuine alternative for the expression of an immunogenic and non-toxic vaccine for the Pulpy Kidney Disease. Thus, in this study, the hypothesis was that the EtxD protein could be transiently expressed efficiently in Nicotiana benthamiana plants via deconstructed viral vectors, targeting the EtxD protein expression into the apoplast or the cytosol. This resulted in the investigation of the following six research topics: 1. The feasibility of producing the Epsilon toxin recombinantly in N. benthamiana. 2. The role of subcellular targeting in the observed level of expression and accumulation of the target protein. 3. The methods of purification that could be explored to recover and purify the EtxD protein that was transiently expressed recombinantly in the N. benthamiana leaves. 4. The suitability of the plant-derived purified EtxD protein as an antigen for Pulpy Kidney Disease vaccine production. 5. An evaluation of the toxicity of the plant-derived EtxD protein. 6. Testing the efficacy of the recombinant plant-derived EtxD antigen. In this context, the EtxD gene, accession number AY858558, and the genetic region from the NCBI and EMBL databases was targeted for this study since the EtxD gene is well-reported in published data and is similar to the EtxD-gene strain produced in South Africa. The targeted gene was then codon-optimised to be expressed in N. benthamiana plants and chemically synthesised by GeneArt. The codon-optimised EtxD gene was directly cloned into an Icon-deconstructed vector and vacuum infiltrated via an Agrobacterium- mediated transfer. Leaves of N. benthamiana were transfected by vacuum infiltration to deliver the EtxD gene transiently into the apoplast and the cytosol respectively. The plant-derived EtxD protein was then isolated from the plant matrix and biochemically analysed by SDS-PAGE, N-terminal peptide sequencing and Western Blot analysis. The EtxD protein was visible as a 34 kDa protein band on an SDS-PAGE gel. The protein band was isolated, and the sequence was confirmed by N-terminal sequencing, as well as by Western Blot analysis using a secondary polyclonal guinea pig anti-EtxD antibody. The plant-derived EtxD protein was then quantified by ELISA and thereafter the expression levels were established at 380 mg/kg fresh weight when targeted to the apoplast, and 300 mg/kg fresh weight when targeted to the cytosol. The apoplast plant-made EtxD protein was purified using a two-step chromatography method, namely ion exchange and size exclusion, with a 50% recovery of the EtxD protein on the final step of purification. To investigate the suitability of the plant-derived purified EtxD protein as an antigen for the Pulpy Kidney Disease vaccine, the toxicity of the EtxD protein was evaluated and the efficacy of the derived EtxD protein was tested. For these, both in vitro and in vivo studies were conducted. The LD50 studies on mice revealed that the plant-derived EtxD protein was slightly toxic, which correlated with the IC50 results on MDCK cells. For the animal-challenge results, two formulations of vaccines were prepared from the recombinant antigen EtxD protein and administered intravenously to mice. The formulations that contained the plant-derived EtxD protein that were not activated by trypsin were unable to protect mice against the Epsilon toxin challenge. This indicates that the Epsilon toxin in the purified plant extract was not immunogenic. When the plant-derived EtxD protein was treated with trypsin, inactivated with formalin and formulated with the adjuvant, alum, it was also non-protective. However, the formulation containing the plant-derived EtxD protein and Disease Control Africa (DCA) immune stimulant was protective. These findings indicated that the plant-derived Epsilon toxin is a viable recombinant antigenic vaccine when formulated with the immune stimulant DCA. In conclusion, this study has demonstrated that tobacco is a suitable host for the production of the EtxD protein. The ELISA results of the infiltrated tobacco leaf samples have demonstrated the successful expression of the 34 kDa EtxD protein together with glucan-endo-1, 3-beta-glucanase of about 25 kDa. The cytosol targeted strategy generated the lowest EtxD protein production at 300, 200 and 10 ?g/kg fw of the protein. For large scale-production of the EtxD protein, transient expression targeting to the apoplast is preferable because of the high yield of protein per fresh leaf weight achieved in this study. / Thesis (PhD)--University of Pretoria, 2016. / Plant Science / PhD / Unrestricted

A substantial number of South African citrus trees are rooted on rough lemon rootstocks. In order to ensure the successful establishment of a high percentage of young citrus trees, it is necessary to ensure that farmers are provided with young vigorous nursery trees that have a large and healthy root system. Vermicast extracts (VE) and liquid extracts from the giant seaweed, Ecklonia maxima (EM), have been used on various crops over the past decades to promote plant growth and development. It is widely reported that plant growth, seedling vigour, water-use efficiency and nutrient-uptake of these crops improves with EM and VE treatments, thereby reducing excessive fertiliser applications. With the improved uptake of nutrients such as nitrogen (N), which is the main component of chloroplasts and proteins involved in the Calvin cycle, it is likely that the application of EM and VE to plants could lead to an improvement in the photosynthetic capacity of plants. The benefits from applications of EM and VE have been attributed to the presence of plant growth regulators/hormones (PGRs) such as auxins and cytokinins. Since seaweed extracts are manufactured using different methods, some of which may include the use of elevated temperatures, acid and/or alkaline hydrolysis of plant material, it is not surprising that different seaweed extracts may contain various levels of PGRs which can lead to dissimilarities in their growth promoting effects. A hydroponic experiment was conducted to test if locally produced EM from two different suppliers and VE would increase root length, root volume, root dry mass, stem diameter, plant height, chlorophyll content, nutrient uptake and photosynthetic capacity of rough lemon seedlings. The other objective of this study was to determine if there was any difference in growth promoting effects of EM obtained from two different supplies due to the difference in the levels of plant growth regulators they contain. Since the action of EM and VE is dose dependant, it was also necessary to determine the optimum concentration of EM and VE for the growth of rough lemon seedlings. This experiment was conducted in a glasshouse at the University of Pretoria experimental farm. Liquefied Ecklonia maxima from different manufactures; Ecklonia maxima - Kelpak® and Ecklonia maxima – Afrikelp® (EM1 & EM2 respectively); and vermicast extracts (VE) were applied separately to rough lemon seedlings as a drench (at 0.5%, 1% and 2% dilutions), at 14 day intervals. Deionized water and full strength Hoagland solution were used as controls. Root volume, root length, stem diameter, plant height, chlorophyll content and photosynthesis were measured weekly for 12 weeks. At the end of the trial, the average root dry mass and shoot dry mass for each treatment was determined. Upon termination of the trial, oven dried leaf samples were analysed for nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca). N analysis was done at an accredited commercial lab whilst P, K and Ca analyses were done at the University of Pretoria using ICP-OES. / Dissertation (MSc (Agric))--University of Pretoria, 2017. / Plant Production and Soil Science / MSc (Agric) / Unrestricted

Extended shelf life (ESL) milk combines longer shelf life and better organoleptic characteristics; a combination that is absent in both pasteurised and ultra-heat treated (UHT) milk. Bacterial spoilage remains the main cause of food loss worldwide, which also includes milk and dairy products, despite advances in food preservation technology. The objectives of this study were to identify and characterise the spore-forming population associated with ESL milk during processing and chilled storage as well as characterising Bacillus cereus isolates obtained from ESL milk processing and during storage. Characterisation of spore-formers associated with ESL milk was done by analysing bacteriological quality of milk samples collected at various processing stages and during storage. Isolates were identified with MALDI-TOF-MS. B. cereus strains obtained from ESL milk and filler nozzles were characterised using (GTG)5 Rep PCR fingerprinting; the presence of virulence genes; cytotoxin K (cytK), nonhemolytic enterotoxin A (nheA), emetic toxin cereulide (cer) and enterotoxin hemolysin BL (hblA). The isolates were further discriminated as psychrotrophic and mesophilic strains using 16S rDNA. Furthermore, B. cereus isolates were selected for 16S partial sequencing. Some of the B. cereus strains obtained from ESL milk and filler nozzles were further characterised using rpoB partial sequencing and multilocus sequence typing (MLST). Milk had spore counts < 2 log10 cfu/ml and 4 log10 cfu/ml during processing and storage, respectively. Bacillus pumilus dominated the bacterial population. In addition B. subtilis, B. cereus, B. sonorensis, B. licheniformis and Paenibacillus spp. were among the main spore-formers identified in the study. Bacterial species were inoculated in sterile milk for a shelf life study and population change observed over 42 days at 7 oC. Despite high prevalence of cer, hblA and nheA; cytK was not widely distributed. There was 100% and 8% prevalence of mesophilic and psychrotrophic signatures, respectively in B. cereus isolates. Although ESL milk process was effective in the reduction of bacterial counts and species diversity, the presence of B. cereus shows a potential safety problem in ESL milk. Despite the large diversity of the B. cereus strains in this study, there is evidence that biofilms associated with filler nozzles and raw milk are a source of contamination of B. cereus in ESL milk. Furthermore, the study has also shown that rpoB partial sequencing and MLST can be used as a tool for source tracking in ESL milk processing. / Thesis (PhD)--University of Pretoria, 2017. / Food Science / PhD / Unrestricted

The most accurate way of quantifying water use or evapotranspiration (ET) is achieved through direct physical measurements. Therefore, quantifying water use of sweet potato using the eddy covariance (EC) system which is one of the direct methods, and calculating crop growth parameters under optimal crop growing conditions, will improve our understanding and crop management practices. Also water scarcity is becoming more and more of a threat to food and nutritional security. Therefore, it is important to produce higher nutrients per unit of water used in order to alleviate malnutrition and to conserve natural water resources. Thus, it is important to do field trials for this crop in order to measure ET and calculate crop coefficient (Kc) to increase transferability of information generated to other scenarios. This information will help to improve agricultural production and livelihoods in arid and semi-arid areas mainly through improving nutritional water productivity (NWP), and irrigation water management within the sweet potato industry. The aim of this study was to: (a) quantify ET dynamics for sweet potato (Ipomoea batatas) in order to determine FAO-type Kc which can be used to estimate crop water use for a range of growing conditions, and (b) to investigate the effects of deficit irrigation on storage root yield, water use efficiency (WUE), nutritional content (NC) nutritional yield (NY) and NWP of commonly cultivated sweet potato cultivars in South Africa (SA) [one orange-flesh (OFSP) ‘Bophelo’ and one white-flesh (WFSP) ‘Blesbok’]. An eddy covariance (EC) system containing energy balance (EB) sensors was installed in a 1.3 ha field with only OFSP variety ‘Bophelo’ in order to quantify the water use. A second trial was composed of 18 plots of 5 m × 4 m (20 m2), with a 2 m border between plots. Six treatment combinations of OFSP and WFSP and three water levels, termed full irrigation (FI), supplementary irrigation (SI) and rainfed (RF) were arranged in a randomized complete block design (RCBD) with three replications at the Agricultural Research Council–Vegetable and Ornamental Plants (ARC–VOP) Gauteng Province, SA. Daily ET varied between 0.5 to 5.5 mm (linked closely to canopy cover and weather conditions), with total seasonal ET measured at 361 and 347 mm for the 2014/2016 and 2015/2016 seasons, respectively. Averaged values of Kc were 0.46, 0.92 and 0.57 during the initial, middle and late growth stages, respectively. Final storage root yields were 32 t ha-1 (2014/2015) and 29 t ha-1 (2015/2016), with WUE of 89 and 85 kg ha-1 mm-1, respectively. The study was conducted during 2014/2015 and 2015/2016 seasons, from January to May in both seasons. / Dissertation (MSc (Agric))--University of Pretoria, 2017. / Plant Production and Soil Science / MSc (Agric) / Unrestricted

Heat waves are, amongst other weather hazards, projected to increase in frequency and intensity due to climate change. This increase has already been evident in parts of South Africa in the recent years. Their negative impacts are felt in many areas, including human health. This study aims to identify the most appropriate meteorological index for forecasting heat waves over South Africa and use it to develop an operational, numerical weather forecast based prediction system that will issue alerts whenever heat waves are expected. Data from temperature and relative humidity subsets from National Centers for Environmental Prediction (NCEP) Ensemble Forecast System (EFS), and observational temperature and dew-point temperature data from the South African Weather Service are used to evaluate and identify the most appropriate meteorological heat index, and to evaluate the model’s skill in heat wave forecasting. A number of evaluation matrices, including bias, symmetric external dependence index and Clayton skill scores, are used for evaluation. Recent heat wave events are also used to identify the synoptic patterns that cause heat waves. This is achieved by plotting the mean sea-level pressure heights and 850hPa and 500hPa geopotential heights from NCEP reanalysis data for these cases. Since there is no evidence that the impacts of heat waves on human health have to date been conducted in South Africa, this study uses international literature to identify the best practices that can be used to prevent or mitigate the negative impacts of heat waves on human health. The Humidex index is identified as the most suitable index for forecasting heat waves over South Africa and has benefit in the skill of up to five days ahead. This implies that heat wave warnings can be issued with confidence 1-5 days ahead of the phenomenon. Eight heat wave cases were identified between 2011 and 2015, and most of them occurred over the eastern interior of the country. These heat waves are caused by the presence of a broad surface trough over the interior that extends from the tropics, with no moisture influx from the Indian Ocean (IO), along with an upper-air high-pressure system over the central interior. Heat waves over the east coast are caused by the presence of a ridging high or continental high that are located in such a way that the east coast is on an off-shore flow. A ridging high that would normally cause berg winds and veld fires over the Western Cape is also the cause of heat waves. The heat-health watch-warning systems in other parts of the world are effective due to the involvement of different stakeholders. The same approach is recommended for adoption over South Africa. With the involvement of different sectors, and with the health sector taking the lead, the system is expected to accomplish the desired outcome. / Dissertation (MSc)--University of Pretoria, 2017. / Geography, Geoinformatics and Meteorology / MSc / Unrestricted

The main focus of this research was to study in detail the selected plant growth promoting bacteria (PGPR) from Bacillus group. PGPR have been described as possible solution to the negative effects of chemicals fertilizers experienced by human beings, other living organisms and the environment through reducing or replacing the use of chemical fertilizers and pesticides. The work aimed at finding plant promotion and plant protection activity of selected PGPR species. Different bioassays were performed in the laboratory and greenhouse to find if the selected bacteria promote plant growth and protect plants through inhibiting pathogens, or protect them during drought conditions. RNA sequencing technology was carried out to study gene expression regulation of a Bacillus atrophaeus UCMB-5137. The selected bacteria showed some plant growth promotion and protection abilities. Bacillus atrophaeus UCMB-5137 and Bacillus amyloliquefaciens ssp. plantarum UCMB-5007 actively promoted wheat growth. All strains showed some pathogen inhibition, while some strains induced drought tolerance abilities. Genes responsible for plant colonization of the Bacillus atrophaeus UCMB-5137 and transcription factors regulating gene expression were identified. This work will create a basis for the possible development of industrially potential biofertilizers and biopesticides for agricultural practices. / Thesis (PhD)--University of Pretoria, 2017. / Biochemistry / PhD / Unrestricted

Savannahs, which are defined as a heterogeneous mixture of herbaceous and woody plant components, occupy one fifth of the global land surface and is the largest biome in South Africa. The woody vegetation structure of savannahs is particularly important as it influences the fire regime, nutrient cycling and the water cycle of these environments and provides fuelwood to sustain the local human populace. Remote Sensing has been proven in numerous studies to be the preferred tool for quantifying and mapping this woody vegetation structure (in this study, defined as woody biomass, woody canopy volume and woody canopy cover metrics) over large areas, mainly due to its superior information gathering capabilities, wide spatial coverage and temporal repeatability. Active remote sensing sensors such as Light Detection and Ranging (LiDAR) and Synthetic Aperture Radar (SAR) are particularly useful in studying woody biomass and other canopy structural metrics, because of their capacity to image within-canopy properties. Passive optical imagery acquired over multiple seasons can also provide tree phenological information which can be used to ascertain the best period for monitoring tree structure, i.e. when tree canopies has sufficient leaves while the grasses are dry. The combined strength of these active (SAR and LiDAR) and passive (optical) sensor technologies, are yet to be applied to their full potential in the dynamic and heterogeneous savannah environment, with a special relevance in Southern African landscapes. This PhD study aimed to evaluate various methods for estimating and upscaling woody structural metrics of South African savannahs using integrated SAR and optical remote sensing datasets and LiDAR datasets as training and validation. Before this aim could be tackled, two current global-scale remote sensing woody structural products (25m JAXA ALOS PALSAR Forest/Non-Forest or FNF and 30m Landsat-based Vegetation Continuous Field or VCF) were evaluated, within the South African context, with the help of high resolution airborne LiDAR datasets. These datasets were resampled to match the products’ criteria and definition used to depict forests. It was found that the FNF product grossly under-represented the distribution of forests in savannah environments (20-80% CC ranges), due to the inadequate HV backscatter threshold chosen in its creation. The FNF product also showed a limited ability in detecting closed forest cover class (90-100%) and Natural Forest and Scrub Forest tree structural classes. The Landsat VCF product displayed strong CC underestimation with increasing variability and mean error from CC values of greater than 30%. The moderate accuracies at the 10-20% CC range (and in the Open Woodland tree structural class) suggests that the VCF product could be potentially applicable in low CC environments such as grasslands and sparse savannahs but can also marginally detect closed canopy environments (90-100% CC range). These results provide the justification for developing new, locally calibrated woody structural products for South Africa. Next, the aim of this study was addressed, firstly, by developing methodologies for the estimation of key woody structural metrics (above ground biomass, woody canopy cover and woody canopy volume) for the Greater Southern Kruger National Park Region using multi-frequency SAR parameters (X-, C- and L-band backscatter and polarisations). Secondly, the most suitable SAR frequency was then tested against and in combination with various Landsat-5 TM optical features (textures, vegetation indices and multi-seasonal band reflectance) for improved regional modelling of woody canopy cover. In both cases, In-situ field measurements of woody vegetation structure were “scaled-up” to landscape and regional scales by using LiDAR, SAR and/or optical sensor products to produce reliable maps of woody structural metrics. A Random Forest modelling approach was predominantly used to meet the modelling challenges in this study and the LiDAR datasets were used for model calibration and validation. / Thesis (PhD)--University of Pretoria, 2017. / Geography, Geoinformatics and Meteorology / PhD / Unrestricted

South Africa has been a net importer of wheat for the past two decades. Due to the inverse relationship between quality and yields, it has been argued that the pursuit of the high wheat quality standards as set by government has led to greater financial loss, rather than financial gain. Various stakeholders in the wheat value chain are said to lose more than they gain from the high quality standards that are required to be maintained. Given the industry claims of the required wheat quality standards being too high, the aim of the study is to evaluate the economic implications of government intervention in the wheat industry through their enforcement of quality standards. The specific objectives of this study have become the determination of historic output changes of bread-baking wheat and non-bread-baking wheat in the South African wheat industry, and to determine the returns from the current government-required wheat quality standards. The Fisher Divisia index method was used to determine the historic output changes of bread-baking wheat and non-bread-baking wheat in the South African wheat industry. It was found that the output of both non-bread-baking and bread-baking wheat quality had a declining rate. However, the output of wheat of bread-baking quality was declining at a faster rate than that of wheat of non-bread-baking quality. To determine the returns from the current wheat quality standards, econometric modelling was used along with a benefit-cost analysis. It was found that the application of quality standards as set in the Agricultural Product Standards Act No. 119 of 1990 (APS) has led to an average total cost of R45.6 million and associated benefits of R28.2 million between 1999 and 2014. This has resulted in a benefit-cost ratio of 0.62. This implies that for every Rand invested in public breeding for quality improvement, 38 cents has been lost. This further suggests that for any amount invested in breeding solely for the purposes of quality improvement, a significant amount has not been recovered. There are therefore cogent reasons to consider reforming the Agricultural Product Standards Act. / Dissertation (MSc (Agric))--University of Pretoria, 2018. / Agricultural Economics, Extension and Rural Development / MSc (Agric) / Unrestricted

Recent advances in semiconductor growth techniques have led to the production of high quality Ge that plays a vital role in the fabrication of electrical devices. Germanium (Ge) is mainly used as a detector material being highly sensitive to X-rays, gamma rays and ionizing radiation, and also shows promise for high speed applications. However, the performance of the devices is strongly influenced by radiation damage. Antimony (Sb), being one of the most common dopants in Ge semiconductor devices, forms the well-known Sb-vacancy complex, also known as the E-center, when the fabricated device is exposed to high energy particle radiation. In this study, the defects induced by high energy alpha-particle irradiation were investigated by means of deep level transient spectroscopy (DLTS). Previous studies found that the DLTS peak traditionally ascribed to the E-center anneals out in two steps, with the first step at room temperature and the second at about 390 K. Possible explanations in the literature for this behavior include interstitials being released by other defects annealing out reacting with the Sb-vacancy. In this study, we have shown that, contrary to previous theories, the DLTS peak that was assigned to the E-center consists of two peaks relating to two defects of similar nature. The peaks were resolved using two techniques: Laplace-DLTS with manual input of regularization parameters and a technique referred to as subtraction of transients. It was found that the peak annealing at high temperatures corresponded to the well-known E-center while the peak annealing at lower temperatures was a new defect which was denoted the E’. Using these techniques, it was shown that, although the two defects had very similar emission characteristics (DLTS signatures: E-center was determined to have an ionization enthalpy of 0.0370±0.005 eV with an apparent capture cross section of 7.9 × 10?15 cm2 while the corresponding values for the E’ were 0.0375±0.005 eV and 6.2 × 10?15 cm2). Other properties of the defects differed significantly, for instance the true capture cross sections at T ? ? were 2.2 × 10?15 cm2 and 1.0 × 10?13 cm2 respectively and the capture barriers were 0.043 eV and 0.092 eV. The annealing activation energy of the E-center was 1.05 eV and that of the E’ was 0.73 eV with frequency factors of 2.5 × 109 s?1 and 2.7 × 108 s?1 respectively. Furthermore, the study showed that the defects had significantly different introduction kinetics, mainly a linear introduction rate for the E-center and the E’ introduced quadratically and being dependent on the introduction and presence of another defect. It is believed that the evidence presented in this study provides conclusive proof for the existence of an up to now unobserved defect in Ge which has up to now been confused with the well-known E-center. / Dissertation (MSc)--University of Pretoria, 2017. / Physics / MSc / Unrestricted

This thesis examines factors influencing smallholder dairy farmers’ participation in interlocked contractual arrangements, the nature and level of participation, the role of interlocked contractual arrangements in promoting smallholder farmers’ participation in markets and the impact of participation on household income. The study seeks to contribute to the ongoing debate about the prospects of these arrangements in enhancing smallholder farmers’ access to restructured and liberalised agrifood markets and whether they truly benefit from participating. The study was carried out in 2014 in the milk shed areas of three districts of Zambia where interlocked contractual arrangements were present. Key informant interviews and focus group discussions were used to collect data from representatives from two financial institutions, four milk collection centres and three milk-processing firms. Semi-structured questionnaires were used to collect data from 266 households engaged in dairy farming. A multi-stage sampling design was used to select these households. Data analysis employed descriptive statistics and econometric regression models. Detailed analysis was carried out by employing measures of dispersion and central tendency, as well as data normality tests. The double-hurdle model was used to identify determinants of smallholder farmers’ participation in interlocked contractual arrangements, while propensity score matching was used to assess the impact of participation on household income. Determinants of smallholder farmers’ decision to sell milk through interlocked contractual arrangements include ownership of improved breed animals, milk price, access to dairy marketing information, income from other sources and landholding size. While most of these factors also affected the proportion of milk sold, the following were important as well: household head education level, cattle-rearing culture, relative supplier’s dependency on buyer and existence of trust in the exchange relationship. Factors adversely affecting farmers’ participation include high stock feed cost, poor breeding programmes, low milk prices, a long time lag for contract review, low participation of women and youths and inadequate involvement in decision-making and transparency in grading. Results further show that ownership of a milk-processing plant and membership to a dairy cooperative enhance smallholder farmers’ involvement in value chain activities but not in key business decision-making. Interlocked contractual arrangements have enhanced smallholder farmers’ participation in the mainstream dairy value chain and access to resources and services, through reduction of information asymmetry and related costs and risks. They have achieved this through the concurrent use of contracts, transaction-specific investments, trust and relational norms. Support from development agencies and public and private sectors is also critical in addressing the multiple market and institutional failures that prevent smallholder farmers from participating in markets. Although results show that smallholder farmers are not excluded from participating in interlocked contractual arrangements, the intensity of their participation is low. Meanwhile, processors are willing to collaborate more with smallholder farmers because of their low side-selling risk. Whereas interlocked contractual arrangements offer prospects to enhance access to financial services and stock feed, much more needs to be done to increase the number of participating farmers. Results also reveal that participation in interlocked contractual arrangements enhances milk revenue but not household income. While interlocked contractual arrangements enhance smallholder farmers’ access to markets, they are not a panacea for addressing the high rural poverty rates. Thus, reorientation from overemphasis on contract farming to a mix of other strategies, such as livelihood diversification. / Thesis (PhD)--University of Pretoria, 2018. / Agricultural Economics, Extension and Rural Development / PhD / Unrestricted