Browsing by Author "Ncube, Bhekumthetho."

Now showing 1 - 5 of 5

Assessment of spatial and temporal variation in water quality of the Pienaars River, Limpopo water management area.
(2018) Mlotshwa, Lungile Wendy.; Tsvuura, Zivanai.; Ndhlala, Ashwell Rungano.; Ncube, Bhekumthetho.
Abstract available in pdf.
In vitro regeneration and secondary metabolites in cyrtanthus species.
(2013) Ncube, Bhekumthetho.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.
Perennial geophytes form part of the diversified flora in southern Africa. The traditional medicinal system, integrates various plant components in the treatment of diverse ailments. In South Africa, bulbs are part of the extensively exploited floral resources for traditional medicine purposes. The reason for selective preference of certain groups of plant species or taxa, particularly geophytes, is rooted primarily on the beliefs that potent constituents are from the underground plant parts. The great surge of public interest in the use of plants as medicines however, assumes that plants will be available on a continuing basis. A vastly increasing human population coupled with the rapid degradation and fragmentation of natural habitats, exacerbate the threats posed by increasing demand on floral resources. The highly endemic members of the genus Cyrtanthus, most of which have limited geographic distribution ranges, are increasingly exploited for traditional medicines in South Africa. Bulbs of this species are the most preferred part for medicinal use, leading to the destructive harvesting of these plants. This form of plant harvesting poses threats to the long term sustainability of these plant resources in their natural habitats. Although sustainable harvesting of plant resources should be within the limits of their capacity for self-renewal, this seldom occurs owing to indiscriminate and destructive harvesting by commercial medicinal plant gatherers. As a consequence of this and other factors, intensive population decimation of a number of Cyrtanthus species is now evident and widespread, with some species threatened with extinction. The extinction of these species could lead to, in addition to the undesirable loss of genetic variability, loss of potential therapeutic agents. Conservation of these plant resources is therefore essential. The aim of this study was to establish efficient in vitro regeneration protocols for three threatened Cyrtanthus species (C. contractus, C. guthrieae and C. obliquus) endemic to southern Africa and explore the possible potential of improving the quality and quantity of bioactive secondary metabolites in culture. In vitro cultured twin-scale explants of the three selected Cyrtanthus species using different concentrations and combinations of 6-benzyladenine (BA) (0, 1.1, 4.4, 6.7, 8.9 μM) and naphthalene acetic acid (NAA) (0, 0.5, 1.1, 2.7 μM) in a 4 x 5 factorial treatment structure, established different optimal PGR combinations for shoot regeneration for each species. The highest shoot induction responses were obtained on MS medium with 4.4 μM BA/1.1 μM NAA for C. contractus and C. guthrieae and 6.7 μM BA/2.7 μM NAA for C. obliquus. The low concentration level of PGR requirements for shoot regeneration in C. contractus and C. guthrieae explants may suggest that the two species contain high enough endogenous hormones to induce shooting compared to those of C. obliquus. When the effect of different types and concentrations of cytokinins (CKs) [BA, kinetin (Kin), meta-topolins (mT), zeatin (ZT) and thidiazuron (TDZ)] on shoot multiplication were evaluated, 5 μM TDZ, 10 μM TDZ and 10 μM BA for C. guthrieae, C. contractus and C. obliquus respectively, were established as the optimum for shoot proliferation in each respective species. These results indicate, TDZ, a characteristically inexpensive CK, to be highly potent and effective in shoot proliferation of C. guthrieae and C. contractus. In terms of visual quality, shoots obtained from media supplemented with Kin and mT resulted in the best quality shoots in all three species at all concentrations tested. Furthermore, Kin also exhibited some auxin-like activitty by inducing rooting and callus on C. contractus and C. guthrieae cultures. The regenerated organogenic calli from C. guthrieae explants produced the optimum number of shoots through indirect organogenesis when transferred to MS medium supplemented with a combination of 0.1 μM picloram and 0.01 μM BA. An almost two-fold shoot proliferation frequency was obtained when the resulting callus-derived microshoots where subsequently transferred to the optimised shoot proliferation medium for the species. Regenerated shoots for all species were rooted successfully on half- and full-strength MS media without plant growth regulators, transferred to organic soil mix, and successfully acclimatised in greenhouse conditions. The developed micropropagation protocols provide a rapid and cost effective way of conservation, domestication and commercial cultivation of Cyrtanthus species. The levels of proline and polyphenolic compounds measured at intervals of three, four and five weeks from initial plantlet culture under different levels of salinity and osmotic regimes, increased in a stress-dependent pattern. The levels of these metabolites also showed a significant increase with an increase in the duration of plantlets under stress conditions. The highest proline concentration (9.98 μmol gˉ¹ FW) was recorded in C. contractus at 300 μM NaCl after five weeks. The high level of total polyphenolic compounds (147 mg GAE gˉ¹ DW) for the same species was however, recorded in the 150 μM NaCl stress treatment. The activity of proline dehydrogenase (PDH) (EC 1.5.99.8) was shown to decrease with an increase in proline levels from week three to week five in almost all stress conditions evaluated. The high levels, particularly of phenolic compounds obtained under osmotic and salinity stress conditions in this study present a promising potential for manipulating culture and/or growing conditions for improved secondary compound production and hence medicinal benefits. In a study of the growth dynamics and patterns of assimilate partitioning to primary and secondary metabolites in response to varying levels and combinations of C (carbon) and N (nitrogen) in the culture media of Cyrtanthus guthrieae, relative growth rate (RGR) increased proportionally with an increase in C concentrations up to 88 mM sucrose (0.58 dˉ¹) beyond which it was hardly influenced by further increases in C. In C-limited media regimes with growth saturating N conditions, alkaloid accumulation became favoured while polyphenol content increased with an increase in C levels in the medium, a characteristic pattern that appeared to be less influenced by the amount of N. Of the primary metabolites, only proteins showed small significant variations across different media treatments, with starch and soluble sugars increasing proportionately with C levels. From a medicinal perspective, with regard to polyphenolic compounds in C. guthrieae, growth media conditions that allow for high levels of C pools in the tissue would thus be favourable for the enhanced synthesis of this group of compounds. The medium conditions with 175 mM sucrose and 10.3 mM NH₄NO₃ gave the highest total polyphenol, flavonoid and proanthocyanidin levels with a moderate growth rate. Pharmacological evaluation of the monthly collected C. contractus bulbs indicated some impressive bioactivities particularly the cytotoxicity effects against human cancer cell lines and enzyme inhibition (AChE and COX) by the extracts collected in certain months of the year. Of notable interest were the cytotoxicity effects, AChE and COX enzymes inhibitory activity of the extracts collected in May and September. Similarly, some extracts from in vitro precursor-fed plantlet and callus cultures demonstrated some excellent bioactivity, against COX and AChE enzymes. The results obtained from this study also reflect on the involvement of the environment in the quality of the extracts produced on a month to month basis and further suggest the importance of coinciding collection and use of plant extracts with the best time of the year or month. The good AChE and COX enzyme inhibitory activity by some of these extracts is of significant importance in the treatment of Alzheimer’s disease and neuroinflammation. The extracts represents an important component of traditional medicine.
Pre- and post-harvest response of selected indigenous leafy vegetables to water stress.
(2018) Maseko, Innocent.; Mabhaudhi, Tafadzwanashe.; Tesfay, Samson Zeray.; Ncube, Bhekumthetho.
South Africa has wide diversity of African leafy vegetables (ALVs) rich in nutrients and adapted to marginal production. However, there is limited availability of ALVs in South Africa due to lack of cultivation owing to limited agronomic and postharvest management information. The increase in population growth, malnutrition and climate change necessitates production of more food using limited water resources. The aim of this study was to evaluate pre and postharvest response of Amaranthus cruentus (pigweed), Vigna unguiculata (cowpea), Corchorus olitorius (Jute mallow) and a reference crop B. vulgaris (Swiss chard) to varying irrigation regimes. The current study consisted of a literature review and five experiments (two agronomic studies and three post-harvest studies. In literature, the performance of ALVs is drawn in comparison to exotic counterparts grown under different conditions; yet agronomic and nutritional factors are only valid when crops are grown under the same condition. Hence in the four experiments of this study, Swiss chard was used as a reference crop grown under same locality. Swiss chard was chosen because it is an alien leafy vegetable that has been indigenised in sub-Saharan Africa and is highly nutritious (contains high levels of Fe, Zn and β-carotene). Before conducting experiments there was need to identify potential gaps and research priorities for this study and even for future research. This was done by conducting a literature review study (Chapter 2) on the status of production and utilisation of ALVs in South Africa for the period 1994–2017. Results of the review indicated that there is a decline in consumption of ALVs partly as a result of limited availability and negative perception. In order to promote ALVs, further research on agronomy, post-harvest handling, storage and processing is required in South Africa. Field and rain shelter experiments were conducted at Roodeplaat, Pretoria, over two summer seasons, 2015/2016 and 2016/2017 to evaluate growth, yield and water-use of selected leafy vegetables under varying water regimes. A randomised complete block design with three replicates was used. The treatments evaluated were: three irrigation regimes (30%, 60% and 100% of crop water requirement (ETc) on three ALVs – Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata and a reference crop, Beta vulgaris. Seeds of A. cruentus and C. olitorius were obtained from the seed bank of the Agricultural Research Council (ARC) - Vegetable and Ornamental Plants (VOP), Roodeplaat, Pretoria seed bank. Vigna unguiculata (Bechuana white, a runner type) and Swiss chard (B. vulgaris L.) cultivar ‘Ford Hook Giant’ seeds were obtained from Hygrotech Seed Pty. Ltd., South Africa. Soil samples were taken from the field prior to land preparation and soil fertility analyses done at the Agricultural Research Council–Institute for Soil, Climate and Water (ARC–ISCW). Nitrogen, phosphate and potassium were applied according to the results and recommendations of the soil fertility analysis for both seasons. Seedlings of A. cruentus, B. vulgaris and C. olitorius were raised in commercial growing medium and covered with vermiculate to minimize water losses from above surface. Vigna unguiculata was sown directly. Seedlings were transplanted at four weeks after sowing. Irrigation scheduling was based on reference evapotranspiration (ET) and a crop factor for each crop. Data collection in field and rain shelter trials included plant height, leaf number, chlorophyll content index (CCI), chlorophyll fluorescence (CF) and yield. In A. cruentus, drought stress (30% ETc) reduced yield consistently in both field and rain shelter trials. Plant height and chlorophyll content index (CCI) were significantly reduced by water stress under field conditions. For C. olitorius, drought stress (30% ETc) reduced yield under rain shelter conditions while all measured parameters were not affected under field conditions. In V. unguiculata, stem fresh mass increased with increase in water application from 30%-60 ETc with no further significant increase under field conditions while all measured parameters showed a similar trend under rain shelter although the results were not significant. In B. vulgaris leaf number, plant height, CCI, yield, Mg, Ca, Na, Zn, and Mn were reduced by water stress for rainshelter. Using 60% ETc proved to be suitable for production of A. cruentus and B. vulgaris var. cicla whereas 30% ETc would be recommended for V. unguiculata. For V. unguiculata and C. olitorius application of 30% ETc is recommended while application of 60% ETc can be used under to slightly improve yield. Amaranthus cruentus and B. vulgaris were comparable in their response to water regimes while C. olitorius and V. unguiculata performed better than B. vulgaris under water stress, an indication of an opportunity to use these vegetables under drought conditions. The evaluation of nutritional quality of A. cruentus, C. olitorius, V. unguiculata and B. vulgaris was motivated by recommendations made in most agronomic studies based on biomass yield with no follow-up on nutritional value. Samples from each crop were collected from each of the three irrigation regimes (30%, 60% and 100%ETc) during each harvest (6, 8 and 10 weeks after transplanting for both seasons) and analysed for macro and micronutrients. Results from A. cruentus indicates that Ca and Mg were significantly higher under drought stress (30% ETc) while Na, K and Zn increased with water application up to 60% ETc with no further increase thereafter. Similarly, Ca and Mg were higher under drought stress and Zn under medium stress in C. olitorius. Calcium was high under drought stress condition in B. vulgaris while Na and Zn where high in medium stress; with a further increase in water application resulting in diminishing returns. Phosphate and potassium were high in medium stress condition in V. unguiculata while in water application up to 100% ETc the two elements showed diminishing returns. The high nutrients alternated between the most severe water stress (30% ETc) and medium stress (60 ETc) treatments across all crops in this study, an indication that although the crops can be grown under drought conditions, slight irrigation can lead to improved production. Leaf Fe, Zn, Mn, Mg and Ca increased with time of harvesting that increased from 6 to 8 weeks, with no further change in nutritional yield when crops were harvested at 10 weeks in A. cruentus, V. unguiculata and B. vulgaris. In C. olitorius, Fe, Zn, Mn, Mg and Na were high when harvested at 6 weeks compared to late harvesting (8 and 10 weeks). The first postharvest study investigated the effect of three irrigation regimes (30%, 60% and 100% ETc) and three drying (sun, oven, shade) methods on phenolic, flavonoid and gallatannin content of the four vegetables. Fully irrigated C. olitorius and subjected to sun drying (100% ETc x sun drying) had higher total phenolic content followed by medium stress subjected to shade drying (60% ETc x shade drying). Furthermore, water stressed plants that were then shade- or sun-dried retained better gallotannin content than other treatment combinations. Amaranthus cruentus grown under drought then shade- or sun-dried (30% ETc x shade and sun drying) retained better quality in all phenolic components measured. In V. unguiculata, phenolic content was high in water-stressed plants subjected to sun-drying (30% ETc x sun drying) while sun drying retained flavonoid and gallotannin than shade and oven drying. In B. vulgaris, well irrigated plants and shade- or oven-dried (100% ETc x shade/oven drying) had better phenolic content. Shade dried leaves had better flavonoid while drought-stressed plants had better gallotannins content compared to other treatments in B. vulgaris. All three ALVs can be grown under drought stress and subjected to sun or shade drying to retain nutrient compared to B. vulgaris. The second experiment on postharvest investigated the interaction of packaging (non-perforated and perforated), temperature [room storage, refrigerated storage (4℃), retail storage, 10℃] and storage duration (2, 4, 6, 8, 10 days) on C. olitorius. Plants rarely experience a single stress factor but are simultaneously exposed to multitude stress factors in their growing environment. The results showed that treatment combination of 4℃ with perforated packaging retains higher phenolic content followed by perforated packaging at 10℃ while lower phenolics were in treatment combinations that were stored at room temperature. Total phenolic content was higher at 2 days and 4 days storage in non-perforated packaging compared to all other treatments combinations. Furthermore, phenolic content decreased disproportionately with storage duration in non-perforated packaging treatment combinations, performing better than perforated in every storage duration. Flavonoid content and total phenolics decreased with increase in storage duration while better retaining these in any treatment combination of 4℃/10℃ compared to room temperature. Phenolic content was significantly higher from 2 to 4 days then declined from 6 through to 10 days at 4℃. At room temperature, phenolic contents decreased from 2 to 4 days storage durations but were higher at 6 and 8 days storage durations before dropping at 10 days. Antioxidant activity and overall acceptance was improved in any treatment combinations kept at 4 and 10℃ compared to room temperature for both types of packaging as storage duration increased. Antioxidant activity and overall acceptance degradation was reduced in treatment combination kept at 4 and 10℃ compared to room temperature for both types of packaging as storage duration increased. Corchorus stored at room temperature had a shelf life of 2 days, but 8 days at 4℃ and 10 days at 10℃ for both types of packaging.
Role of fertilisation regimes on the yield and nutritional benefiits of cowpeaamaranth intercropping systems.
(2020) Mndzebele, Buhlebelive Melusi Mgcini Phiwayinkosi.; Modi, Albert Thembinkosi.; Mabhaudhi, Tafadzwanashe.; Ncube, Bhekumthetho.
Several African leafy vegetables (ALVs) contribute to food and nutritional security of rural communities, particularly due to their ability to grow in marginal soils. These ALVs such as amaranth and cowpea among others provide valuable macro- and micronutrients that are key to rural household dietary needs. The aim of this study was to assess the effect of fertiliser application on the symbiotic nitrogen fixation, enzymatic phosphatase activity, agro biological properties, nutrition as well as recommended daily allowance in an intercropped Amaranthus cruentus (amaranth) and Vigna unguiculata (cowpea) farming system. The nitrogen fixation and nutritional yield of cowpea-amaranth intercrop study was motivated by limited information relating symbiotic nitrogen fixation and fertilisation of ALVs, such as cowpea and amaranth grown under intercropping system, in addition to nutritional yield. Field trials were conducted at the Agricultural Research Council (ARC), Vegetables and Ornamental Plants campus situated in Roodeplaat, Pretoria, South Africa, during 2014/15 and 2015/16 summer seasons from November to January. The 2 x 4 factorial experiments were laid out in a completely randomized design (CRD) with four replications. The factors evaluated were intercropping (amaranth and cowpea) and fertiliser (control, 25%, 50%, and 100% of the recommended NPK levels). Soil sampling was done before land preparation and soil nutrient analysis was done at the Agricultural Research Council–Soil, Climate and Water (ARC–SCW). The application of nitrogen, phosphorus and potassium were guided by the soil analyses results and recommendations on both seasons. Vigna unguiculata was sown directly in the soils and amaranth was transplanted approximately four weeks after planting amaranth in the nursery. Irrigation was done based on reference evapotranspiration (ET) and a crop factor for each crop. Collected data included acid and alkaline phosphatase activity, phosphorus in the soils, phosphorus in the cowpea and amaranth plants, as well as biomass of cowpea and amaranth at physiological maturity. In the rhizosphere of cowpea and amaranth grown as sole crops, there was a higher acid and alkaline phosphatase activity as compared to those on intercropping. The highest rhizospheric phosphatase activity occurred when both crops were grown without fertilizer or 25% NPK. Applying NPK activates soil-bound phosphorus (P) using root exudates, which is important for the production of ALVs. The results showed a reduction in symbiotic N2 fixation of cowpea with the increase fertiliser addition. The above ground and above ground edible biomass of amaranth increased proportionately to the rate of fertiliser application up to 100% NPK, but in cowpea it only increased up to 50% NPK. Nutritional yield of iron and zinc increased with the increase in fertiliser application amounts on cowpea and amaranth. The land utilisation values were greater than one, hence an advantage of intercropping. Cowpea was more aggressive, showed high actual yield losses and high competitive ratio relative to amaranth. More income could be obtained from intercropping cowpea and amaranth compared to the respective sole crops at 100% NPK. In the experiment on the potential of intercropped amaranth and cowpea to meet nutritional requirements, the seasonal above ground and above ground edible biomass of amaranth and cowpea increased with fertiliser application up to 100% NPK. More above ground and above ground edible biomass on amaranth and cowpea were obtained in sole cropping when compared to intercropping. Macro and trace nutritional element contents were highest at 100% NPK fertiliser level. The lowest nutritional contents of macro and trace elements was recorded at the control. Overall, amaranth and cowpea contributed to the recommended daily allowance of calcium, magnesium, iron, and zinc, where there was more at the 100% NPK fertiliser level. The research demonstrates the benefits of grain leguminous crops in soil nutrient fertility enhancement and inorganic fertilization with intercropping in managing micronutrient deficiency to meet the nutritional needs of rural communities. Moreover, the study demonstrated the benefit of applying 25%NPK to 50%NPK fertiliser on the above ground and above ground edible biomass of amaranth and cowpea. In sum, macro and trace elements that are crucial for the nutritional health of rural communities were improved, thus contributing more to the recommended daily allowance, which limits food and nutrition insecurity, and fosters sustainable development.
Seasonal pharmacological and phytochemical properties of medicinal bulbs.
(2010) Ncube, Bhekumthetho.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.
Medicinal bulbs form part of the diversified flora in South Africa. The plants are used extensively in South African traditional medicine in the treatment of various ailments. Due to the ever-increasing demand and the unrestricted collection of medicinal plants from the wild, many of these slow growing bulbous plant species are driven into over-exploitation and extinction. The main parts collected for use are the underground bulbs, leading to the destructive harvesting of the whole plant. This form of plant harvesting poses threats to the long term sustainability of these plant resources from their natural habitats. Sustainable harvesting of these plants should be within the limits of their capacity for self-renewal. However, this seldom occurs with the often inconsiderate medicinal plant gatherers. Conservation of these plants is therefore necessary. A strategy that would take into consideration the sustainable harvesting and perhaps simultaneously provide similar medicinal benefits, would be the substitution of bulbs with leaves of the same plant. This study was aimed at evaluating the seasonal pharmacological and phytochemical properties in bulbs/corms and leaves of medicinal bulbs with a view of promoting the substitution of bulbs with leaves in traditional medicinal use. Four medicinal bulbous plants, Tulbaghia violacea, Hypoxis hemerocallidea, Drimia robusta and Merwilla plumbea were evaluated for the pharmacological and phytochemical properties in their bulbs/corms and leaves in spring, summer, autumn and winter seasons, with a view of promoting the use of leaves as a conservation strategy. Dried plant materials were sequentially extracted with petroleum ether (PE), dichloromethane (DCM), 80% ethanol (EtOH) and water in each season. The extracts were tested for activities against Gram-positive (Bacillus subtilis and Staphylococcus aureus), Gram-negative (Escherichia coli and Klebsiella pneumoniae) bacteria and the fungus Candida albicans using the in vitro microdilution assays to obtain minimum inhibitory concentrations (MIC) and minimum fungicidal concentrations (MFC). The four plant species were also evaluated for their ability to inhibit cyclooxygenase (COX-1 and COX-2) enzymes. Spectrophotometric methods were used to evaluate saponin and phenolic contents of samples from the four plant species in each season. Antibacterial activity was fairly comparable between bulbs/corms and leaves of H. hemerocallidea, T. violacea, and M. plumbea, with at least one extract showing some good activity (MIC < 1 mg/ml) in most of the seasons. Bulb extracts of D. robusta did not show good antibacterial activity while the leaf extracts showed good activity (0.78 mg/ml) against B. subtilis in spring, summer, and autumn and S. aureus (0.78 mg/ml) in autumn. The best antibacterial activity was recorded in winter, with MIC values as low as 0.195 mg/ml from the DCM bulb extracts of T. violacea against K. pneumoniae and S. aureus and PE corm extracts of H. hemerocallidea (0.195 mg/ml) against B. subtilis. Good antibacterial activity from water extracts were only recorded from corm extracts of H. hemerocallidea in summer, autumn and winter, H. hemerocallidea leaf extracts in autumn and winter, and M. plumbea bulb extracts in autumn. The leaf extracts of all the screened plant species demonstrated good fungicidal activity in autumn, with H. hemerocallidea corm water extracts recording an MFC value as low as 0.39 mg/ml. The leaf extracts of H. hemerocallidea (water), D. robusta (DCM) and M. plumbea (DCM) had good MFC values of 0.78 mg/ml each, in spring. The DCM leaf extracts of T. violacea also showed good fungicidal activity (0.78 mg/ml) in summer, while corm water extracts of H. hemerocallidea had an MFC value of 0.39 mg/ml in winter. There were no fungicidal activities recorded from all the bulb extracts in all the seasons. All the PE and DCM extracts in all the tested plant samples recorded between moderate (40-70%) and high (> 70%) COX-1 and COX-2 inhibition levels across all seasons. The EtOH corm extracts of H. hemerocallidea also demonstrated moderate to high inhibitory activity against COX-1 enzyme across all seasons. Bulb and leaf extracts of T. violacea showed selective inhibitory activity for COX-2 enzyme in all the seasons. The highest COX inhibitory levels were recorded in COX-2 from the PE leaf (spring) and bulb (autumn) extracts of T. violacea, with both recording 100% inhibitory activity. Phytochemical analysis revealed higher total phenolic compounds in bulbs/corms and leaves of all the analysed plant species, to be either higher in spring or winter. Plant material collected in autumn had the least levels of total phenolics. An almost similar trend to that of total phenolics was observed for flavonoids, gallotannins and condensed tannins in most plant samples, with higher levels either in spring or winter. Total saponins were consistently higher in winter than in the other seasons in all the screened plant species. There were in some cases, relationships between the peaks in the levels of some phytochemical compounds and the observed levels of bioactivity in different assays. The results obtained from this study demonstrate that the leaves of the screened plant species may substitute or complement bulbs in the treatment of certain ailments in traditional medicine. Thus, plant part substitution can be sustainably utilised in the conservation of these plant species while retaining the same medicinal benefits.