Browsing by Author "Chibarabada, Tendai Polite."

Now showing 1 - 2 of 2

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 Irrigation was withdrawn thereafter in all water treatments to determine physiological and metabolic responses (total soluble sugars, antioxidants and phenols) to terminal stress.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.
Water use and nutritional water productivity of selected major and underutilised grain legumes.
(2018) Chibarabada, Tendai Polite.; Modi, Albert Thembinkosi.
Grain legumes have potential to alleviate the prevalence of food and nutrition security in water scarce areas. There is need to promote underutilised grain legumes to diversify crop production and build resilience. This requires knowledge on their water use (ET), environmental adaptation and nutritional content (NC) in comparison to major legumes. The study benchmarked underutilised grain legumes [bambara groundnut (Vigna subterranea) and cowpea (Vigna unguiculata)] to major grain legumes [groundnut (Arachis hypogaea) and dry bean (Phaseolus vulgaris)] with respect to ET, water productivity (WP), NC and nutritional water productivity (NWP). Field experiments were conducted during the 2015/16 and 2016/17 summer seasons under varying water regimes [optimum irrigation (OI), deficit irrigation (DI) and rainfed (RF)] and environmental conditions (Ukulinga, Fountainhill and Umbumbulu) in KwaZulu-Natal, South Africa. Data collected included stomatal conductance, leaf area index, timing of key phenological stages and yield. Water use was calculated as a residual of the soil water balance. Water productivity was calculated as the quotient of grain yield and ET. Grain was analysed for protein, fat, Ca, Fe and Zn. Yield, ET and NC were used to compute NWP. Results from the field trials were used calibrate and test the performance of AquaCrop model for groundnut and dry bean. Under varying water regimes, crops adapted to limited soil water through stomatal regulation and reduction in canopy size and duration. Yield, yield components and WP varied significantly (P < 0.05) among crop species. During 2015/16, groundnut had the highest yield and WP under DI (10 540 kg ha-1 and 0.99 kg m-3, respectively). During 2016/17, the highest yield and WP were observed in dry bean under DI (2 911 kg ha-1 and 0.75 kg m-3, respectively). For both seasons, dry bean had the lowest ET across all water treatments (143 – 268 mm). Dry bean and groundnut out–performed bambara groundnut with respect to yield, harvest index and WP. Yield varied significantly (P < 0.05) across environments and seasons. Cowpea was the most stable species. Results of NWP were significant among crops (P < 0.05). Yield instability caused fluctuations in NWP. Groundnut had the highest NWPfat (46 – 406 g m-3). Groundnut and dry bean had the highest NWPprotein (29 – 314 g m-3). For NWPFe, Zn and Ca, dry bean and cowpea were more productive. Overall, the AquaCrop model was successfully calibrated for groundnut and dry beans. Model testing showed AquaCrop’s potential for simulating growth, yield and ET of groundnut and dry bean under semi-arid conditions. Underutilised grain legumes need to undergo crop improvement for successful promotion. There is need to improve adaptation of grain legumes to different environments and resilience to extreme weather events. Future studies should consider benchmarking more underutilised grain legumes to major grain legumes.