School of Animal, Plant and Environmental Sciences (ETDs)

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Browsing School of Animal, Plant and Environmental Sciences (ETDs) by SDG "SDG-12: Responsible consumption and production"

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    The effects of elevated carbon dioxide concentrations on the physiological and biological characteristics of Portulacaria afra
    (University of the Witwatersrand, Johannesburg, 2024) Basson, Domonique Courtney; Risenga, Ida
    There is a concern that rising atmospheric carbon dioxide (CO₂) concentrations may affect the medicinal or nutritional profile of medicinal plants. Portulacaria afra (P. afra) is a medicinal plant used by traditional healers to treat various skin conditions. The aim of this study was to determine whether elevated CO2 concentrations will affect the physiological and medicinal properties of the leaves, stems, and roots of P. afra. This was achieved by measuring the physiological, phytochemical, antioxidant, and antimicrobial activity of the various plant parts, which were exposed to ambient (420 ppm) and elevated (600 ppm) CO₂ concentrations and comparing them to samples grown in greenhouse conditions. The plant samples were placed in a Conviron climate stimulator for three months. Three harvests were completed during thistime. The physiological properties measured include the weight of the various plant parts as well as the chlorophyll content within the leaves. The phytochemical profile of the plant was examined through a set of standard colour tests (qualitative analysis) and the determination of the total flavonoid content (quantitative analysis) in all three plant parts exposed to the various treatments. The antioxidant activity was determined by analysing the scavenging activity of the extracts against 1,1 diphenyl-2- picrylhydrazel (DPPH) and hydrogen peroxide (H2O2) with the use of a spectrophotometer. The antimicrobial activity determined the extracts’ ability to inhibit the growth of six microorganisms related to skin conditions. The results of this study revealed that there was a 65% and 39% increase in the weight of the leaves and roots, which were exposed to 600 ppm, respectively. A higher phytochemical presence was recorded in plants exposed to 600 ppm. There was a significant increase in flavonoid presence and flavonoid content in the methanolic and hot water plant samples that were exposed to elevated CO2.The leaves, stems, and roots of P. afra exhibit strong scavenging activity against DPPH and even more so towards H2O2. The strongest antioxidant activity was 13 exhibited by the methanolic leaf extracts which were exposed to 600 ppm, against H2O2 (0.2±0.7 mg/ml). The antimicrobial activity of all three plant parts was relatively constant between the different treatments. Despite the relatively weak antimicrobial activity of P. afra (MIC values > 1000 (µg/ml), a notable increase in the antimicrobial activity of the leaves against Cutibacterium. acnes were observed in samples exposed to 600 ppm of CO₂. Portulacaria afra is a medicinal plant that exhibits great resilience towards elevated atmospheric CO2 concentrations. The phytochemical and biological properties in this study displayed either no change or an increase in activity, which suggests that P. afra may continue to provide relief against certain ailments in the future despite rising atmospheric CO2 concentrations
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    The reproductive system of Campuloclinium macrocephalum and its implications for biocontrol implementation
    (University of the Witwatersrand, Johannesburg, 2022) Moodley, Saness; Glennon, Kelsey; Goodman-Cron, Glynis
    Invasive species are a threat to biodiversity therefore it is imperative to determine the factors that facilitate the invasion potential of a species. Campuloclinium macrocephalum Less. (DC), the ‘pompom weed’, is an alien invasive species in South Africa and is currently threatening the persistence of the grassland, wetland, and savanna biomes. The species is also significantly contributing to a decline in plant diversity by outcompeting native vegetation in these areas. Various integrated approaches using combinations of chemical, mechanical and biocontrol management programs have been developed to manage the spread of the species in its invaded range, however the species has still been able to persist. The persistence of the species was hypothesised to be a consequence of the co-occurrence of apomixis and polyploidy, however despite the identification of triploid and tetraploid cytotypes in South African populations of the pompom weed, the reproductive strategy of the species has not yet been determined. The aim of this study was therefore to infer whether populations of C. macrocephalum (pompom weed) reproduces via vector-mediated crosses, self-pollination or apomixis (either facultative or obligate) and examine the relationship of the mode of reproduction with ploidy level. Male fertility was also assessed to ascertain if interploidy gene flow was possible. The collated information was then used to infer the potential impact of reproductive strategies and polyploidy on biocontrol. All examined populations were shown to have high mean pollen viability percentages of 90% and 98% with no significant differences in pollen viability amongst the four populations. The high pollen viability percentages were supported by prolific pollen grain germination on the stigmatic surfaces (margins of style at base of style branches) and the sides of the style. This suggested that the pollen grains can fertilize and interploidy mating is likely possible in South African populations of the pompom weed. It is plausible that the high pollen viability is enabling triploids to act as a ‘triploid bridge’. However, the high pollen viability was confounded by the pollen tube analyses revealing that pollen tube growth is being arrested on the stigmatic surface suggesting that overall male fertility is low. The arrested pollen tube growth is typically associated with a ‘triploid block’. Nevertheless, the production of viable gametes can reduce the triploid block and facilitate gene flow between populations. The predominant mode of reproduction was determined by assessing the contribution of insects to pollen transfer, pollinator exclusion experiments, germination trials, pollen tube growth to the ovules and genetic analyses. We found that the African Monarch butterfly (Danaus chrysippus) and the honeybee (Apis mellifera) contributed most to pollen transfer in comparison to the other insects visiting C. macrocephalum. A pollinator exclusion experiment showed that the pompom weed can set seed in the absence of pollinators, albeit at lower quantities than in the open treatments. Nevertheless, germination percentages showed that reproductive success was similar between open and bagged treatments in each population. The Modderfontein population showed lower reproductive success and seedling establishment in comparison to the other populations, presumably due to the severity of the biocontrol infestation on this population. Genetic analyses revealed low genetic variation within and amongst populations. Pollen tube analyses showed no pollen tube growth to the ovules in all samples, which suggests that seed set is independent of fertilization. The lack of pollen tube growth is a strong indicator of obligate autonomous apomixis which is further corroborated by the low genetic differentiation between maternal plants and their respective offspring. The co-occurrence of apomixis and polyploidy made it difficult to discern which factor contributes more to the invasiveness of the species, however, we hypothesise that autonomous apomixis provides the pompom weed with the competitive advantage to persist in its invaded range. However, further studies on the reproductive strategies of tetraploid cytotypes are needed to confirm this hypothesis. The low genetic variation suggests that all populations should be equally susceptible to biocontrol agents, however that this may be affected by other factors such as environmental conditions or phenotypic plasticity. Phenotype plasticity refers to a single genotype producing different phenotypes in response to environmental conditions. This could reduce the efficacy of biocontrol agents as they may exhibit differential responses on different phenotypes