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Masters Degrees (Crop Science)

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Browsing Masters Degrees (Crop Science) by Subject "Bambara groundnut--Seeds--Quality."

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    Responses of Bambara groundnut (Vigna Subterannea L. Verdc) landraces to field and controlled environment conditions of water stress.
    (2012) Zondi, Lungelwa Zandile.; Modi, Albert Thembinkosi.
    Bambara groundnut (Vigna subterranea L. Verdc) is a drought tolerant African legume capable of producing reasonable yields where other crops may fail. However, it remains an underutilised crop, owing to limited research, cultivated using landraces, of which scant information is available describing their agronomy and genetic diversity. The aim of this study was to evaluate the response of bambara landraces from different geographical locations to water stress under controlled and field conditions. Seeds were sourced from subsistence farmers of Tugela Ferry and Deepdale in KwaZulu-Natal (South Africa) and Zimbabwe, and characterised into three seed coat colours: light-brown, brown and red. Seed quality was assessed using the standard germination test. Vigour indices of germination velocity index and mean germination time were determined. Seedling establishment was evaluated using seedling trays using a factorial experiment, with four factors: 1. provenance – (Tugela Ferry and Deepdale), 2. seed colour – (red, light-brown and brown), 3. water regimes – (30%, 60% and 100% field capacity), and 4. soil media – (clay, sand and clay + sand). Seedling leaf samples were used to evaluate proline accumulation as an indicator of stress tolerance. A field trial was used to evaluate productivity of bambara landraces under rainfed and irrigated conditions. A pot trial was conducted under controlled environment conditions with three factors: temperature (33/27°C and 21/15°C), water regimes (30% and 100% of crop water requirement) and bambara landrace selections. Results showed no significant differences in germination capacity between bambara landrace selections. Germination time differed significantly (P<0.001) between bambara landrace selections. The Jozini provenance was shown to perform best, followed by Zimbabwe, Tugela Ferry and Deepdale. Brown landrace selections had higher (P<0.001) germination compared with red and light-brown selections, respectively. Seedling establishment showed that emergence was higher (P<0.001) at 100% FC compared with 60% FC and 30% FC. Emergence was higher (P<0.001) in the Sand+Clay mixture compared with Clay and Sand media. Dark-coloured selections had higher (P<0.001) emergence compared with light-coloured selections. Results from the field trial showed that the red landrace selections emerged better (P<0.001) than the light-brown and brown landrace selections, respectively. Plant growth was lower under irrigated compared with rainfed conditions. Stomatal conductance was higher (P<0.001) under irrigated compared with rainfed conditions, whereas chlorophyll content index was higher (P<0.05) under rainfed compared with irrigated conditions. Results of the pot trial showed that emergence was significantly (P<0.001) affected by temperature. It was higher at 33/27°C compared with 21/15°C (P<0.001). Dark-coloured landraces had higher emergence compared with the light-brown landraces. Stomatal conductance was lower at 30% ET relative to 100% ETc. There were no significant differences between water regimes with respect to biomass, pod number per plant, pod mass per plant, seed number per pod, seed mass per plant and harvest index. It is concluded that seed colour is an important variable in the identity of bambara landraces. Provenance plays a significant role in seed performance and there is a significant interaction between provenance and seed coat colour. This study could be expanded to obtain more data for crop improvement through inclusion of many sites and seasons for better agronomic advice to farmers.
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    Seed quality and water use characteristics of a bambara groundnut (Vigna subterranea L.) landrace differing in seed coat colour.
    (2014) Chibarabada, Tendai Polite.; Modi, Albert Thembinkosi.
    Bambara groundnut (Vigna subterranea L.) is an underutilised African legume that fits the same ecological niche as Arachis hypogea (groundnuts). Because of its reported drought tolerance and high water use efficiency there are now renewed efforts to study bambara groundnut with a view to promoting it as an alternative crop in marginal production areas. It is still cultivated using unimproved landraces, and little is known about their seed quality. There is need for information describing aspects of their seed quality in order for farmers to successfully produce the crop. The study evaluated seed quality and seedling water use characteristics of selected seed coat colours of bambara groundnut. Lastly, the study investigated the effect of water stress imposed on maternal plants on subsequent yield and seed quality of bambara groundnut. A single bambara groundnut landrace was characterised into four distinct selections based on seed coat and speckling colour; plain red, plain cream, cream with brown speckles (brown speckled) and cream with black speckles (black speckled). Seed quality (viability and vigour) was evaluated using the standard germination, electrolyte conductivity and imbibition tests as well as water activity, seed coat thickness and mineralogy. Seedling water use characteristics were evaluated under varying water regimes (25%, 50% and 75% field capacity). Measurements included plant growth and physiological (chlorophyll content index and chlorophyll fluorescence) responses up to 21 days after planting; thereafter seedling water use efficiency was determined. Irrigation was withdrawn thereafter in all water treatments to determine physiological and metabolic responses (total soluble sugars, antioxidants and phenols) to terminal stress. A field trial was grown in 2013/14 summer season under irrigated and rainfed conditions. Yield and yield components as well as subsequent seed quality (viability and vigour) of progeny was determined from harvested material. Darker coloured seeds and seeds with similarly coloured speckles showed better viability while the plain cream landrace selection was more vigorous. Seedling water use efficiency in bambara groundnut improved with decreasing water availability. Drought avoidance strategies and acclimation to water stress were also found to be present at the seedling establishment stage. Yield was negatively affected by water stress. Subsequent seed viability and vigour were respectively higher in seeds produced under irrigated and rainfed conditions. The study concluded that although bambara groundnut is a water use efficient crop, water stress may affect yield and subsequent seed quality.