Theses and Dissertations

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    Modelling the Transmission Dynamics of Banana Xanthomon as Wilt Disease with Control Measures
    (Mapinda, John Joel, 2020-03) Mapinda, John Joel
    Banana Xanthomonas Wilt disease (BXW) is a bacterial disease which highly threaten ba nana production in East and Central Africa. It is caused by a bacteria known as Xanthomonas campestris pv. musacearum (Xcm). Mathematical modelling gives an insight on how to best understand the transmission dynamics and control of the disease. The existing mathematical models for the dynamics of BXW disease have not included contaminated soil, community farming education programmes and clearance of Xcm bacteria in the soil. This study formu lated a model which includes contaminated soil. In analysis of the model, the existence and stability of the equilibrium points was checked, calculated the basic reproduction number and carried out sensitivity analysis of some model parameters. We further conducted numerical simulation to validate the results. The numerical simulations showed that the infection rate by contaminated farming tools (βi and βe), the infection rate by contaminated soil (ω2), vertical disease transmission rate (θ), and the shedding rate of Xcm bacteria in the soil (φ) are posi tively sensitive to the basic reproduction number. While, the most negative sensitive parameters are the clearance rate of Xcm bacteria from the soil (µh), removal of infected plants from the farm (r), harvesting (αp), and banana plants disease induced death rate (d). The result also showed that contaminated soil contributes to the transmission and persistence of BXW dis ease. Furthermore, the basic model was modified to include the control measures. Numerical simulations was conducted to examine the impact of the suggested control measures. It was observed that as Participatory community farming education programmes, timely removal of infected banana plants, clearance of Xcm bacteria in the soil and vertical transmission control measures increases it dramatically reduces the number of secondary infections hence greatly contribute to the control of the BXW disease. Therefore, It is recommend that, along with the existing control measures such as sterilization of farming tools, timely removal of the male bud using a forked stick and planting healthy suckers, scientist and technologist should carry out studies to find a way to reduce or avoid vertical disease transmission and increase the Xcm clearance rate in the soil. Furthermore, technology for early detection of infected plants should be brought down to the local farmers at affordable costs. This will help stakeholders to detect and remove the infected plants from the farm in time and hence reduce the number of sec ondary infections. Moreover, Participatory community farming education programmes such as Farmers field schools (FFS) should be emphasized and practised.
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    THE IMPACT OF LAND COVER AND LAND USE ON THE HYDROLOGIC RESPONSE IN THE OLIFANTS
    (University of the Witwatersrand, Johannesburg, 2006) Ncube, Mthokozisi
    Water availability in Southern Africa is highly variable both in time and space, thereby exposing the region to high risks in water availability. This is further compounded by numerous human activities which have significant impact on water resources. The brunt of the risks associated with water scarcity is particularly heaviest on resource- constrained farmers who depend largely on rain-fed agriculture for subsistence. With continuously increasing demands on the water resources, the need for a better understanding of the hydrological systems becomes crucial as it forms the gateway for providing reliable information for managing water resources. It is also increasingly becoming more important to address land and water linkages because land use decisions are water use decisions. Operational hydrology provides an insight into the effects of man-made changes, the foreseeable hydrological characteristics at a given site, and the long-term prediction of the future hydrological effects of human activities. This provides for a more holistic approach in managing land and water resources as well as the impact of land use on partitioning rainfall into streamflow. This report discusses the application of the SWAT model to the B72E - F quaternary catchments in the Olifants Water Management Area to assess streamflow generation and the effects of human-environment interactions on the hydrology. Results show an expected correlation between land cover and the hydrologic response where an increase in land cover corresponds to a reduction in the streamflow. Range grass shows a higher reduction in the streamflow followed by forestry with arid land giving the highest increase in streamflow. Prediction in the similar neighbouring and ungauged B72A catchment gives a MAR of 68mm. Additionally, a rigorous analysis of the concepts of a local hydrological model, HDAM, is done with respect to rainfall which is the main driver of the model. Modifications of some of the relationships used in the model are suggested with the potential of streamlining the model and making it more applicable in the region.