Theses and Dissertations (Plant Science)

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A taxonomic revision of Lachnaea L. (Thymelaeaceae)
(University of Pretoria, 2000) Van Wyk, Abraham Erasmus (Braam); Beyers, Josephine Bertha Pauline
Lachnaea L., a genus endemic to the Cape Floristic Region, occurs almost exclusively in fynbos vegetation. In this revision a brief taxonomic history of Lachnaea is presented. Palynology and chromosome numbers were found to be taxonomically insignificant at specific level. Evidence from macromorphology, leaf anatomy, ecology and geographical distribution is used as the basis for species delimitation. Circumscription of the genus is extended to include the species of Cryptadenia Meisn. Previously proposed sections in Lachnaea are not upheld. Four species and all varieties are reduced to synonymy; 12 species and two subspecies are newly described and one new name is proposed. Forty species and two subspecies are now recognised. Geographically most species are concentrated in the 3319 (Worcester) grid. A phylogenetic hypothesis of Lachnaea resulting from two cladistic analyses is presented. The results of the analyses show that Lachnaea is monophyletic and that the sections are paraphyletic. The two analyses produced mixed resolution regarding the solitary-flowered species and gave conflicting results with regard to the evolutionary pathway of certain characters. Allopatric speciation appears to have been the dominant process in Lachnaea. Additional variables that may have governed diversification are altitudinal difference, allochory and post-fire regeneration strategies. The taxonomic treatment includes keys to the species and subspecies, detailed descriptions with notes on nomenclature, diagnostic features, relationships, distribution, ecology and conservation status. Line drawings and a distribution map are provided for each species.
Contributions to the ethnobotany of the Southern Ndebele
(University of Pretoria, 2011-11) Van Wyk, Abraham Erasmus (Braam); Skosana, Vusi Jackson
Plants have never been formally recorded in the Southern Ndebele language (isiNdebele). A need to investigate this aspect has resulted in the present study, which has been undertaken to identify and record the ethnobotanical (biocultural) significance of selected plants in Southern Ndebele, one of the 11 official languages of South Africa. The Southern Ndebele have a long history dating back to the early 1600s when the group first split from the original Zulu kingdom and entered the interior of South Africa. Even with such a long history, no comprehensive list of plant names in Southern Ndebele has been compiled to date. However, such a list has been recorded for the Northern Ndebele of Zimbabwe, also a Nguni language. The Southern Ndebele of South Africa and the Northern Ndebele of Zimbabwe (also known as the 'Matabele') are distantly related, each group, however, maintaining its own culture and other practices. For purposes of this study yet another language, Northern Ndebele of South Africa, is considered as distinct from Northern Ndebele of Zimbabwe. The Northern Ndebele of South Africa consist of the Gegana group that went further north and settled around Potgietersrus (now Mokopane), Zebediela, Mashashane and other areas in the vicinity of Polokwane (formerly Pietersburg). Their language (known as Sumayela or siNdebele by some scholars) is currently not recognised as a provincial or national language. Speakers of Northern Ndebele are therefore probably often counted as speakers of Northern Sotho (Sepedi), one of the 11 official languages of South Africa and spoken predominantly in Limpopo Province. Although the two Ndebele language groups of South Africa are geographically close to one another, plant names in Northern Ndebele of South Africa have not been considered in the present study. The term Southern Ndebele is used mainly to refer to all people who speak the similarly named language. Although the majority of this cultural group reside in the former KwaNdebele homeland, much of the region now forms part of Mpumalanga Province. Even though the study was conducted in a particular area of Mpumalanga, speakers of Southern Ndebele are not necessarily confined to Mpumalanga, but are widespread across South Africa. A qualitative survey was undertaken by conducting a number of one-on-one and group interviews with knowledgeable elders and professionals who know and understand the Southern Ndebele tradition and culture. Their views, experiences and perceptions about the plants used by the Southern Ndebele were recorded (supplied on a DVD accompanying this report). Voucher specimens of the plants were collected and deposited in the H. G. W .J. Schweickerdt Herbarium [PRU], Department of Plant Science, University of Pretoria. The multiple uses of the plants identified as well as the associated cultural beliefs and traditional conservation measures as practised by the Southern Ndebele, were recorded. The recording and listing of plants in Southern N debele could go a long way to ensure better communication, enhanced teaching and improved conservation practices. The study focused mainly on woody plants, most of which are native to South Africa, as well as on a few alien species useful to the Southern Ndebele. A list of shrubs and some herbaceous indigenous healing plants is also included in this report. Names of more than 100 plant species and infraspecific taxa are presented alphabetically according to scientific name. Also supplied are the family name, the Southern Ndebele name, and the locality and number of the relevant voucher specimen. As a Southern Ndebele by birth, the author has included his personal insight and knowledge of some of the plant names as well as some cultural background information as part of the introduction to the Southern Ndebele. A list of all Southern Ndebele terms/words and plant names used in the study is supplied to clarify and explain their meaning.
Gene expression study of candidate Arabidopsis defence genes in response to the bacterial wilt pathogen, Ralstonia solanacearum
(University of Pretoria, 2015) Berger, David Kenneth; Naidoo, Sanushka; dave.berger@fabi.up.ac.za; Kgoale, Degracious Moloko
Arabidopsis thaliana is a model plant widely used to gain insights in the so called plant-pathogen interactions. This is so because plants are sessile organisms living in an environment rich in disease causing microbes. In contrast, plants cannot relocate to avoid pathogen attacks like animals. As a result, plants rely on their immune responses to rapidly detect invading pathogens so as to fight and defend themselves against pathogens. Over the years, Ralstonia solanacearum has been recognised as an economically important causal agent of bacterial wilt in a vast distribution of plants ranging from important solanaceous crops, leguminous plants, a few monocotyledonous plants (Genin & Boucher, 2002) to major forest trees such as Eucalyptus (Coutinho et al., 2000). It has been documented that R. solanacearum affects over 200 plant species representing 50 botanical families (Hayward, 1991). Thus it is of utmost importance to gain as much insight into this devastating phytopathogen in order to accomplish better control methods. Chemical control is not an option for bacterial diseases, in contrast to fungal diseases. Integrated Pest Management (IPM) of bacterial wilt is considered to be a sustainable approach (Smith, 2000). Hence there is a need to generate disease resistant plants as part of IPM of bacterial wilt across the world. The first step in understanding resistance is to study compatible host plant responses to infection with R. solanacearum. A fascinating discovery was that A. thaliana is a compatible host to bacterial wilt. This has built a strong foundation, a step forward to gaining knowledge as to what happens in a host plant upon R. solanacearum infection. The study of the A. thaliana - R. solanacearum pathosystem has revealed that different ecotypes of Arabidopsis have different responses to the bacterium. Resistant and tolerant ecotypes of Arabidopsis are due to the possession of the recessive gene, AtRRS1-R on chromosome five. The RRS1-R protein physically interacts with an effector protein from the Type III Secretion System (T3SS) of R. solanacearum called PopP2 to elicit Effector Triggered Immunity (ETI) (Coutinho et al., 2000; Deslandes et al., 1998; Deslandes et al., 2002; Deslandes et al., 2003). The interaction thereof is strongly suggested to localise in the nucleus of the host plant involving at least two more A. thaliana proteins, RPS4 (Narusaka et al., 2009) and RD9 (Rivas, 2012). This further suggests that Arabidopsis responses to bacterial wilt involve an extensive cascade of distinct genes.
'n Ekologiese studie van die plantegroei van 'n noordelike en suidelike kloof van die Magaliesberge
(University of Pretoria, 1961-06) Janse van Vuuren, Daniel Rudolph
English: The vegetation of the two kloofs in the Magaliesberg range is described. These kloofs are 10 miles west of the Hartebeespoortdam in die Brits district covering an area of approximately 35 morgen. The altitude of the area varies from 4200 to 5200 feet above sea level. Geologically the region is situated within the Pretoria Series of the Transvaal System and consists of Magaliesberg Quartzites and Magaliesberg Shales. The soils conform very closely to the geological structure. They are residual and formed in situ. Owing to the mountainous topography there has been alluvial drift. The average annual rainfall of the area is 696.7 mm. measured at Wolhuterskop, of which 85% falls during the summer months October to March. There is an indication that the precipitation is higher at the top of the mountain than at the base, and also higher on the south side of the mountain than on the north side. The temperatures of the north and south sides of those. the mountain as well as those of the slopes of the kloofs are compared. Maximum temperatures are lower at the top of the mountain than at the base while minimum temperatures are higher at the top. Temperatures in general are higher on the north side. The temperatures of the slopes of the kloofs, receiving the greater insolation, are higher than those of the opposite slopes. The influence of biotic factors on the vegetation is discussed. The vegetation is classified according to the method described by Goodall (1953) into 16 groups. These 16 groups are described as belonging to the following six communities:- 1. Mimusops-Chrysophyllum-community. 2. Rauvolfia-community. 3. Croton-community 4. Chrysophyllum-community 5. Acacia caffra-community 6. Acalypha glabrata-community. The Mimuso-Chrysophyllum-community occupies most of the west slope and small patches of the lower portion of the east slope of the north kloof. The dominant trees are Mimusops zeyheri and Chrysophyllum magalismontanum. The Rauvolfia-community is confined to the streambanks in the north kloof. This community is characterized by the tropical element in the flora. Rauvolfia caffra is the dominant tree, while species such as Trema guineenais, Ilex mitis, Pygeum africanum_and Pittosporum viridiflorum are present. The east slope of the north kloof is occupied by the Croton-community. This is a dry open community with Croton- subgratissimus, Combretum zeyheri and Combretum holosericeum being the dominant trees. The Chrysophyllum-community covers the western slopes of the kloof near the northern top of the mountain. Chrysophyllum magalismontanum is the dominant tree. Trees such as Cornbretum holosericeum and Ochna pulchra are important constituents of the tree layer. The Acacia caffra-community occupies the slopes of the south kloof and small parts of the upper portion of the north kloof. This community is dominated by Acacia caffra. In the parts of the north kloof where the Acacia caffracommunity occurs, some of the associated species show an affinity with the Bushveld flora. Species such as Combretum zeyheri, Crysophyllum magalismontanum and Mimusops zeyheri are found in this community. On the south side the associated species are mostly widely distributed species, such as Dombeya rotundifolia and Euclea,_lanceolata. The Acalypha glabrata-community occupies the streambanks of the south kloof. The dominant tree is Buddle salicifolia, a specie of the Kalahari Thornveld. Calondendrum_capense and Celtis_africana, temperate forest species, form on important consituent of the tree layer. The vegetation of the north side of the range is dominated by Bushveld species, but a number of tropical forest species are present, e.g. Rauvolfia caffra, Pittosporum viridiflorum, Pygeum africanum and Trema guineensis. The vegetation of the south side of the mountain is dominated by widely distributed species, but there are traces of temperate or transitional forest, with species such as Celtis africana, Kiggelaria africana, Halleria lucida, Leucosidea sericea, Buddleja salvifolia and Cassinopsis ilicifolius.
The evaluation of traditionally used medicinal plants against targets associated with COVID-19
(University of Pretoria, 2023) Lall, Namrita; De Canha, Marco; Reid, Anna-Mari; u15190723@tuks.co.za; Alston, Brandon James
Covid-19 infection is characterized by multiple stages of symptoms, from mild flu-like symptoms to pneumonia and potential death. The sudden nature of the pandemic warranted immediate treatment and the repurposing of existing drugs was prioritized. Multiple vaccines are approved by the Food and Drug Administration (FDA) to limit the infection rate but there is still a need for the targeted treatment of Covid-19. This study evaluated selected medicinal plants based on their traditional use and the available literature on their ethnopharmacology. Ethanolic extracts of the samples were tested for activity against specific targets associated with Covid-19. The number of samples was filtered down to provide lead candidates for future research. Many of the extracts tested on human lung fibroblast (MRC-5) cells in the current study have not been tested on the cell line before. Of the selected plants, Aspalathus linearis, Bulbine frutescens, Clausena anisata, Capparis tomentosa, Foeniculum vulgare, Myrsine africana, Podocarpus latifolius, Polygala virgata, Rhoicissus tridentata and Tylosema esculentum reported no toxicity (IC50 > 400 μg/ml). Factor Xa plays an important role in blood coagulation through the process of activating prothrombin to thrombin. Foeniculum. vulgare, M. africana, P. latifolius and R. tridentata exhibited varying anticoagulant activity. Both R. tridentata (139.10 ± 4.70 μg/ml) and P. latifolius (193.45 ± 10.35 μg/ml) showed the greatest anticoagulant potential. This is the first report of both M. africana and R. tridentata being studied for their FXa inhibitory activity. Cytochrome P450 enzymes are essential in the metabolism of many important drugs. The potential herb-drug interactions were tested F. vulgare, M. africana, P. latifolius and R. tridentata against CYP 1A2, CYP 2C9, CYP 2C19, CYP 2D6 and CYP3A4. Myrsine africana showed increased activity in all CYP P450 enzymes tested when compared to the 100 % 14 activity control. Foeniculum vulgare and R. tridentata showed increased activity of CYP 1A2, CYP 2C9, CYP 2D6 and CYP 3A4. Furthermore, P. latifolius increased the activity of CYP 1A2, CYP 2D6 and CYP 3A4 activity but notably inhibited CYP 2C19 and CYP 2C9. Covid-19 infection causes an inflammatory response known as cytokine release syndrome. When tested against human inflammatory cytokines, F. vulgare and M. africana decreased IL- 6 expression (48 % and 24 % respectively) at 100 μg/ml, although at 200 μg/ml, M. africana showed a 77% increase in IL-6 expression. Furthermore, F. vulgare and M. africana inhibited the expression of IL-8 by 36% and 64% respectively (100 μg/ml) and 27 % and 36 % respectively at 200 μg/ml. Podocarpus latifolius showed inhibition of IL- 12p70 (22 %), IL-6 (66 %) and IL-8 (77 %) at 100 μg/ml and increased expression of IL-12p70 (24 %), TNF-α (98 %), IL-6 (113 %) and IL- 8 (78 %) at 200 μg/ml. Rhoicissus tridentata exhibited 12 % inhibition of IL- 6 at 100 μg/ml while inhibiting IL-8 expression (47 % at 100 μg/ml and 51% at 200 μg/ml) and increasing the expression of IL- 6 (23 %) and TNF-α (120 %) at 200 μg/ml. After evaluation of the selected extracts against targets associated with Covid-19 infection, four lead candidates displayed potential for further investigation. The chosen extracts exhibited good activity on different targets in this study suggesting further assessment into combination studies and the possible identification of bioactive compounds. Treatment targeted specifically at Covid-19 is still needed. This study explores the possibility for a plant derived product to fill this gap and provides the initial steps towards further research targeted towards this goal. This current study is the first report of both FXa inhibition and anti-inflammatory studies against pro-inflammatory cytokines in M. africana and R. tridentata.
Haploid-inducer development by CRISPR/Cas9 mediated CenH3 gene modification in Helianthus annuus (Sunflower)
(University of Pretoria, 2023) Crampton, Bridget Genevieve; Swanevelder, Zacharias Hendrik; u18258566@tuks.co.za; Mabuza, Londiwe M.
Sunflower is the third most important oil seed crop globally following soybean and rapeseed. Climate change threatens crop production with various limitations, including unpredictable temperature fluctuations, altered rainfall patterns and, novel diseases and pests. Conventional, mutation and accelerated breeding technologies, such as haploidization, have been able to address some of these challenges through the production of resistant cultivars. The production of sunflower doubled haploid lines through in vitro approaches such as anther, pollen and unpollinated ovule culturing have been tested with little success, mainly due to sunflower being recalcitrant to tissue culture regeneration. A universal in vivo technique based on the modification of the CenH3 gene leads to uniparental chromosome elimination during hybridisation with a wild type line. This technique has been successfully demonstrated to induce a small number of haploid progenies in Arabidopsis thaliana, maize and wheat. Given the universal function and conserved nature of the CENH3 protein, this approach promises to be a breakthrough in haploid induction technology. The aim of the current study was to facilitate the production of a sunflower haploid inducer line through CENH3 protein modification using the CRISPR/Cas9 technology. Two CRISPR/Cas9 constructs were designed to target three different amino acids (P51S, G52E and A55V) in the histone fold domain region of the sunflower CENH3 through homology directed repair (HDR). The individual constructs (pDe-Cas-258-nptII, pDe-Cas-1185-bar) were introduced to sunflower mature cotyledons by Agrobacterium-mediated transformation while the geminiviral construct (IL-60-BS-Cas9-1185) was mechanically introduced into sunflower seedlings. Next generation sequencing revealed that only four of the transgenics obtained via Agrobacterium transformation contained two of the targeted amino acid conversions (P51S and A55V) and the other three did not contain any mutations. 20% of the plants inoculated with the geminiviral construct displayed mutations, with one plant displaying complete homology directed repair. Furthermore, a slight increase in HDR was observed with the use of a geminiviral vector when compared to Agrobacterium mediated transformation. Sunflower mutant plants were tested for their ability to act as haploid inducers using flow cytometry. Flow cytometric analysis revealed 71% and 12.5% aneuploidy in the T1 and T2 generations, respectively. No haploid progeny was obtained in either generation. The overall results of this study indicate that uniparental chromosome elimination coupled with the use of viral vectors for the delivery of CRISPR/Cas9 components into plant cells, have the potential to improve double haploid technology in sunflower. The research carried out in this study will enhance the improvement of sunflower through genome editing and the production of doubled haploid lines.
Gene silencing mediated by dsRNA reduces grey leaf spot disease in maize
(University of Pretoria, 2023) Berger, David Kenneth; Theron, Jacques; carla.buitendag@up.ac.za; Buitendag, Carla
Grey leaf spot (GLS) is a devastating fungal foliar disease which affects maize globally. The causal agent for GLS in southern Africa is Cercospora zeina. Current methods to control GLS include chemical fungicides and tilling. However, GLS remains a destructive disease with up to 60% yield losses reported in susceptible hybrids. Advances in plant biotechnology utilize a natural gene silencing mechanism known as RNA interference (RNAi). RNAi is mediated by double-stranded RNA (dsRNA) that targets the expression of genes that share sequence complementarity with the dsRNA. This phenomenon has been adapted in new crop protection strategies such as spray-induced gene silencing (SIGS), which involves the external application of dsRNA that targets pathogenicity genes to combat disease. SIGS is a gene-specific, environmentally friendly, biodegradable, and safe treatment. In a previous study from our research group a dsRNA construct was generated which targets three pathogenicity genes in C. zeina. The in vivo results indicated that this dsRNA construct significantly reduced the fungal cell viability (α = 0.05). In this study, the aim was to test the ability of the dsRNA construct to control GLS disease in planta. Maize leaves were inoculated with C. zeina conidia and treated with the dsRNA construct or a negative dsRNA treatment control, Green fluorescent protein (GFP) dsRNA. In addition, the percentage of germinated conidia over a 24-h period was determined in vitro with light microscopy (LM) and in planta using scanning electron microscopy (SEM). This study demonstrated that the dsRNA construct significantly reduced GLS disease symptoms, compared to the positive disease control (α = 0.05). The GFP dsRNA treatments resulted in similar GLS disease symptoms as the positive disease control. A new dsRNA construct was created based on previous successful SIGS studies in Botrytis cinerea, which had demonstrated efficient disease control using the application of external dsRNA. The new dsRNA construct designed in this study will be evaluated in future studies with the aim to obtain highly effective SIGS results in C. zeina which produce almost no GLS symptoms in maize. This study demonstrates promising results that RNAi technologies such as SIGS could be used to control GLS disease in maize.
Aggressiveness of diverse African isolates of Cercospora zeina on maize
(University of Pretoria, 2022) Berger, David Kenneth; Nsibo, David L.; u14237459@tuks.co.za; Mokgobu, Tumisang
Cercospora zeina the causal agent of grey leaf spot of maize causes up to 67% yield losses when susceptible maize cultivars are planted. Variations in the levels of aggressiveness of C. zeina isolates have been reported previously. However, none of the previous studies links the variation in their levels of aggressiveness to the genetic diversity. This study links the genetic diversity within and between African populations of C. zeina isolates to differences in aggressiveness. In this study, the variation in the aggressiveness of five C. zeina isolates (CEDV05074, CMW25467, ZWRRS263, UGKPC38, and KEKER468) was assessed using six quantitative traits namely, incubation period, infection efficiency, lesion size, disease severity index (DSI), area under disease progression curve (AUDPC) and sporulation capacity. Our findings reveal that the genetic diversity previously observed in the C. zeina isolates influences their level of aggressiveness. From this study, we noted the need to standardize the protocol for assessing the infection efficiency and the timing for measuring lesion size in the maize-C. zeina pathosystem. Our findings also proved that hybrid-3 was the most susceptible hybrid and therefore will be used for future aggressiveness assays. Lastly, the identity of the five C. zeina isolates was confirmed using four molecular tools namely, CTB7 gene region, mating type genes, internal transcribed spacer (ITS) gene region, and microsatellite markers. Overall, this study is a step towards mechanisms involved in the pathogenicity of C. zeina. Furthermore, using isolates with high aggressiveness is key for maximizing selection gain when using artificial inoculation to assess maize plant resistance to GLS disease.
Induced antibiotic resistance and staphyloxanthin as a prospective target for treatment against pathogenic antibiotic-resistant staphylococci
(University of Pretoria, 2023) Meyer, Jacobus Johannes Marion; u10066846@tuks.co.za; Mushomba, Martin Mbugua
The past century saw the discovery of antibiotics as an effective treatment for bacterial infections. Life-threatening infections that were previously untreatable could now be neutralized by antibiotics with few side effects. However, in recent years this once effective treatment has become less efficient as the bacteria it once treated are becoming increasingly resistant. Antibiotic resistance presents a major concern in human public health not just on a national level, but potentially at a global level. The development of bacterial resistance to antibiotics is a natural response to stress. Plants have always been an important source of medicines and treatments. In cases where bacteria have become resistant to antibiotics, there have been notable successes in re-establishing antibiotic effectiveness when the antibiotics were used in combination with antibacterial plant extracts. The aim of this study was to compare the metabolites of an initially susceptible wild-type (WT) Staphylococcus with its mutated strain which had lost its antibiotic susceptibility. The mutated antibiotic resistant strain was made by exposing the susceptible WT strain to starvation stress. Metabolites from both strains were then extracted in methanol and analysed by 1H-NMR. Multivariate analyses of the NMR spectra showed significant differences in metabolites between the WT and resistant strains. LC-MS and GC-MS analyses of methanolic bacterial extracts showed that staphyloxanthin, a carotenoid that aids in pathogenesis and protects against oxidative stress was partially identified in low concentration from the WT strain. This was confirmed by comparing mass spectra with data on the NIST (National Institute of Standards and Technology) library database. The susceptible WT strain produced two staphyloxanthin precursors, compounds very similar to the two long chain parts of staphyloxanthin, while the resistant strain did not produce any detectable staphyloxanthin or its precursors. The precursors detected by GC-MS analysis and determined from the NIST Library were similar to squalene and tetradecanoic acid. These were the long hydrocarbon chains on the staphyloxanthin structure. This comparative model of analysing a WT and its consequently resistant strain could also be used as a platform to test the effectiveness of different plant treatments against bacterial defence mechanisms like staphyloxanthin. Focusing on the mechanisms of resistance without impeding bacterial growth might reduce the rate of adaptive resistance in-turn, thereby reducing the rate of antibiotic resistance during antibiotic therapy.
Vegetation in an age of global change : encroachment, succession, and phenology
(University of Pretoria, 2022) Greve, Michelle; Daniel, Kissling; samanthajamison07@gmail.com; Jamison-Daniels, Samantha-Leigh
To successfully predict how ecosystems and associated species will respond to global change drivers, an understanding of the underlying drivers of the assembly, diversity and functional responses of biological communities is needed. The objective of this thesis was to provide insights into the ecology of vegetation through means of exploring phenological and successional patterns and drivers in an age of global change. First, using herbarium records, the timing and climatic drivers of fruiting phenology of 58 widespread South African fleshy- and dry-fruited tree species, which possess different physiological requirements, were tested. Second, the patterns of succession through bush clump formation (a form of woody encroachment) in a South African savanna were explored, and the microclimatic determinants of succession determined. Third, a systematic review to assess whether consistent trends exist in plant functional traits across successional gradients, and to assess whether a bias exists in trait-based successional studies (e.g., between geographic distribution, growth forms, and vegetation types) was conducted. Significant differences in fruiting phenology of fleshy- and dry-fruited species were found: fleshy-fruited species fruited earlier than dry-fruited species, and the effects of climatic predictors on fruiting phenology across species depended on fruiting type: only fleshy-fruited species were limited by winter temperatures, while high temperature seasonality typically resulted in later fruiting for both fleshy- and dry-fruited species. Bush clump formation was initiated by the establishment of a founder individual which resulted in microclimatic changes, facilitating the establishment of other species, and resulting in a deterministic successional change (as bush clump size increased) from an open habitat (characterised by savanna species) to a closed habitat (characterised by forest species). Out of 398 recorded traits reported in successional studies, only six were frequently reported across trait-based successional studies; however, all traits showed consistent trends across successional gradients. Clear biases in trait-based successional studies were observed: woody communities have been studied more often than herbaceous communities, with forest communities being disproportionally studied; and most studies have been conducted in Europe. By linking patterns of phenology and succession to environmental drivers, the impacts that global change drivers may have on community assembly patterns could be inferred. The dependence of phenology on climatic factors suggests that climate change will result in shifts in phenology with implications for seed dispersal and food availability of frugivorous animals. Changes in the microclimate conditions brought about by the associated succession of bush clump formation suggests that microclimate plays a role in the replacement of ancient savannas by forest species; such replacement will compromise the diversity and ecosystem services of savannas. This suggests that management interventions should include processes that naturally keep the system open, such as fire. Finally, our ability to generalise how traits change with succession, over broad vegetation types and geographic regions, is mostly limited to forest systems, and consistent trends observed may not hold in other biomes. Therefore, in a changing, disturbance-driven world in which succession may become increasingly important in community assembly, it is pertinent to predict how communities other than forests, and non-woody taxa, assemble post-disturbance.
The functional biogeography of African acacias (Vachellia and Senegalia) at adult and seedling life stages
(University of Pretoria, 2022) Greve, Michelle; Oberlander, Kenneth; u16078030@tuks.co.za; Milne, Laura
Savannas constitute the largest biome on the African continent. Savanna systems are characterised by the coexistence of C4 grasses in the understorey and trees or shrubs in the overstorey. This balance is maintained by gradients of rainfall, fire and herbivory, which influence woody cover by limiting tree recruitment and persistence. Therefore, in order to persist in savannas, trees must possess adaptations to withstand these limiting factors. The aim of this thesis was to investigate the trait biogeography of African savanna trees of the Mimosoid clade, which is one of three taxa dominating the woody component of African savannas. More specifically, I assessed whether trait trade-offs exist, if fire, herbivory and precipitation drive species trait variation, and whether trait syndromes associated with fire, herbivory and precipitation exist, for a) southern African mimosoid seedlings and for b) African acacias (Vachellia and Senegalia). To measure seedling traits, twelve mimosoid species were grown in an experimental setup and several above- and belowground traits were recorded at an age of 60 days. To measure adult traits, a trait database was compiled using species descriptions of acacias from literature. Estimates of water stress, fire regime and browser biomass experienced across the distribution range of each species were extracted from macroecological maps. Linear models detected trade-offs between traits of adult Senegalia species only and revealed trait responses to aridity, fire and browser predictors for both seedlings and adults. Hierarchical clustering, t-tests and an NMDS ordination analysis were used to show drought severity was the only predictor that differed between the two trait clusters and formed a syndrome at the seedling stage. Adult syndromes were identified using hierarchical clustering, principal component analysis and canonical discriminant analysis; both Vachellia and Senegalia had four species clusters linked to different combinations of aridity, fire and browser gradients. The provenance of savanna species influenced the traits of woody species at both the seedling and adult stages. At the seedling stage, traits reflected strategies to secure a water supply and develop large resilient seedlings to avoid desiccation for species from arid areas. Certain adaptations seem to remain from seedling to adult stages, such as reduced leaf area in arid-adapted species or shorter architectures in species from highly browsed areas. In contrast, some strategies show the opposite trend in seedlings versus adults. Recovery strategies were prioritised in seedling species that originated from areas subjected to intense fire or browsing. In contrast, resistance strategies were prioritised in the adult stage and some strategies indicate a broad adaptation to more than one savanna driver. These findings have important ecological implications as they indicate how traits at both the seedling and the adult stage may offer resistance or tolerance to environmental pressures that would control woody densification and bush encroachment.
The evolution and persistence of polyploidy in Oxalis obliquifolia Steud. ex A.Rich. populations in Gauteng
(University of Pretoria, 2022) Oberlander, Kenneth; Greve, Michelle; u11304775@tuks.co.za; Vaz de Sousa, Damian
Background: Polyploidy is a major factor in the adaptation and speciation of many plant lineages. Many evolutionary factors may contribute to autopolyploid frequency within plant populations, including rates of new polyploid formation, the ability of new polyploids to establish successfully, long-term persistence of polyploids in the environment, and the ability of new polyploids to expand their range. Despite recent progress, there are still many questions regarding polyploid success, in spite of the challenges posed by minority cytotype exclusion, and relatively little is known about ploidy variation in the South African Flora. Aims and objectives: Oxalis obliquifolia Steud. ex A.Rich. is notable for its large distribution range (from the Cape to Ethiopia) and high degree of morphological variability. The aims of this investigation were to document the occurrence of different cytotypes of O. obliquifolia across Gauteng Province, South Africa, and assess the impact of empirical data on theories that attempt to explain polyploid persistence in populations. The objectives of the study were: firstly, to sample individuals of O. obliquifolia across Gauteng and assess their cytotype using flow cytometry and chromosome squashes; secondly, to determine if there were differences in abiotic niches occupied by different cytotypes; thirdly, to determine the morphological and phenological traits associated with polyploidy; fourthly, to assess the degree of reproductive isolation between different cytotypes; and finally, to assess the degree of relatedness between individuals of different ploidy-levels across mixed-ploidy sites. Methods: Over 320 samples from 25 sites were collected and cytotyped, using standard flow cytometric and ploidy confirmed using meiotic chromosome squashes. Individuals were mapped and abiotic variables assessed for correlations with cytotype distribution using GIS, climate data, field observations, soil data, and ordinations and PerMANOVAs. Different cytotypes (100 individuals, including diploids, tetraploids and hexaploids) were grown under identical conditions to assess the associations between polyploidy and morphology and phenology, and results were analysed using linear models and discriminant analyses. Reproductive isolation and frequency of polyploidisation were assessed using crossing experiments (1140 crosses, with different maternal cytotypes), as well as AMOVA analyses based on Internal Transcribed Spacer DNA sequences. Results: Remarkably, six distinct cytotypes were identified, with over 50% of sites comprising multiple ploidies. Abiotic variables were not associated with cytotype distribution possibly due to scale. The common garden experiment demonstrated a clear Gigas effect, which may confer a competitive advantage for polyploids over their smaller diploid progenitors. Larger flowers and differences in flowering phenology suggest pollinator interactions may play a role in enabling polyploid persistence. Crosses between cytotypes are possible under artificial settings, however DNA analysis suggests diploids and polyploids are reproductively isolated in the wild, and that polyploidisation is not a frequent enough event to explain the high levels of cytotype sympatry observed. Diploids and polyploids are behaving as separate species, despite high sympatry and non-zero potential inter-cytotype seed set. Tests on biotic interactions may provide insights into how polyploids have flourished in this system.
Broad- and fine-scale vegetation patterns in the Waterberg, South Africa
(University of Pretoria, 2022) Le Roux, Peter; Barker, Nigel P.; tamrynsventer@gmail.com; Venter, Tamryn S.
Natural areas are under threat due to land transformation, placing additional pressure on existing protected areas and emphasizing the need for more conserved areas. However, effective conservation planning requires considerable biodiversity data to identify priority areas for conservation, despite many areas being poorly sampled. The Waterberg, a mountainous area in the Savanna Biome in Limpopo, South Africa, is floristically relatively poorly known and currently vulnerable to land conversion. The aim of this study was, therefore, to better understand vegetation patterns in the Waterberg, so to inform conservation efforts in the region. First, a vascular plant species list was compiled (mainly from online datasets) for the Waterberg Mountain Complex, comprising 2722 taxa from 901 genera, 182 families, and 61 orders. This includes 27 endemic taxa (percentage endemism: 0.99%) and 49 taxa of conservation concern. The Waterberg displays a high diversity of genera and families, comparable to other species-rich areas including the Soutpansberg and the Cape Floristic Region. The current estimates of the vascular plant endemism in the Waterberg are too low for the region to be considered a centre of plant endemism, but with its rich higher-order diversity the Waterberg could potentially be considered a centre of floristic diversity. Species composition in the Waterberg is relatively similar to two other mountainous areas in the Savanna Biome: the Magaliesberg and the Soutpansberg. However, the Waterberg was the most under-sampled of the three areas. Second, the transferability of plant richness models between two large Waterberg reserves was tested to examine if the richness-environment relationship from one reserve can accurately estimate richness patterns in the other reserve. When richness models demonstrate good transferability, they allow accurate modelling of biodiversity for understudied regions. However, models for six plant richness variables (total species, grass species, herb species, woody species, genus, and family richness), based on a set of 16 predictor variables all consistently showed poor transferability. This result was independent of the three modelling approaches used, which varied the number of predictor variables and/or minimized differences in environmental conditions between the two reserves. The poor transferability of these richness models possibly reflects the degree to which each reserve contains novel environments absent from the other reserve as well as the aggregative nature of richness variables (i.e. they are the sum of the occurrence patterns of different species, with each species potentially responding differently to multiple components in the environment). The plant richness models from this research are currently not useful for predicting richness to other areas in the Waterberg, due to their poor transferability. However, as the Waterberg region has a high plant diversity and has generally been poorly sampled, it is important to continue conducting more botanical surveys in the area while simultaneously trying to improve plant richness models as a secondary measure to address biodiversity gaps for the region. The combination of additional floristic surveys and spatial models of biodiversity data will help to inform conservation decisions in the Waterberg.
The role of dispersal mechanisms in range shifts of plant species across sub-Antarctic Marion Island
(University of Pretoria, 2022-09) Le Roux, Peter; Greve, Michelle; u13107021@tuks.co.za; Mazibuko, Nompilo
Dispersal is a key lifecycle event and is the means through which species spread geographically, across both fine and broad scales. Despite their ecological importance, dispersal events have proven challenging to quantify as they are often difficult to observe and measure accurately. An attempt to overcome this has been the use of mechanistic models and standardised experiments that combine theory and experimental data to simulate dispersal events that occur through wind, animals, water, and anthropogenic activity. The dispersal estimates obtained using such methods can be useful in multiple ways, including being incorporated into species distribution models to gain ecological and evolutionary insight into the current and future distributions of species across landscapes. Indeed, studies that include dispersal potential have developed more accurate predictions of how species and ecosystems respond to changing environmental conditions. Here, I use mechanistic modelling and standardised experiments to conduct the first quantification of the dispersal potential of the dominant vascular flora in the sub-Antarctic (via anemochory, thalassochory, zoochory, and anthropogenic activity) and test whether species’ dispersal capacity is correlated with inter-specific variation in recent changes in species’ ranges. My results show that species dispersal potential is not correlated with the magnitude of species range expansion for both native and alien species. Inter-specific variation in range expansion was also not related to species’ habitat specificity or functional traits, suggesting that other mechanisms (e.g. demography, competition, and/or the thermal requirements and nutrient demands of species) must be responsible for the variation observed in species range expansion rates. Since my findings contradict ecological theory and evidence from several other dispersal-focused studies, I conclude by reviewing the literature regarding methods for estimating dispersal and present suggestions about how these methods can be integrated to improve our understanding of the effects of dispersal at local scales. While there have been considerable advancements in methods for quantifying dispersal (especially where long-distance dispersal is concerned), this research shows that there is still room for improvement in how we study dispersal events and their effects at smaller scales.
Fungal diversity of [Tylosema esculentum (Burch.) A.Schreib.] and T. fassoglense (Kotschy ex Schweinf). Torre & Hillc. seeds, leaves and tubers from South Africa
(University of Pretoria, 2022) Kritzinger, Quenton; Truter, Mariëtte; Barker, Nigel; Schonfeldt, H.C. (Hettie Carina); u15071538@tuks.co.za; Armfield, Taryn Jean
The marama bean, encompassing both Tylosema esculentum ((Burch.) A.Schreib.) and Tylosema fassoglense ((Kotschy ex Schweinf.) Torre & Hillc.), has been identified as an orphan crop of southern Africa with a great potential for commercialisation. The potential of the marama bean to be developed into a valuable crop poses a question regarding possible biotic constraints, including fungal pathogens and mycotoxigenic fungi. This study investigates the mycoflora and mycotoxins associated with marama bean in South Africa, as well as the potential pathogenicity and mycotoxigenicity of various fungal species on the marama bean. Various fungal isolates were obtained from marama bean leaves, seeds and tubers collected from eight locations in South Africa, ranging from the Gauteng and North West to Limpopo and Mpumalanga provinces. The various fungal isolates were identified using a dual morphological and molecular approach. A total of 116 species spanning 27 families were molecularly identified, several of which have been previously reported on marama beans in Namibia, including various Alternaria, Epicoccum, Fusarium, Penicillium, Phoma and Rhizopus species. Other notable fungal genera isolated from the South African marama bean include Aspergillus, Lasiodiplodia, Neofusicoccum, Botryosphaeria, Chaetomium, Diaporthe, Bipolaris, Pestalotiopsis, Neopestalotiopsis, and Talaromyces. Multi-mycotoxin analysis was performed on the plant material as well as on isolated fungal cultures in vitro using maize patty cultures, focusing on Aspergillus, Fusarium and Penicillium. Several of the species analysed indicated the potential to produce aflatoxin iii B1 and fumonisins B1, B2 and B3 in vitro, however, no mycotoxins were detected in any of the collected plant material. Twenty of the fungal isolates (spanning thirteen different species) were selected to investigate the potential of the fungal species to be pathogenic to the marama bean, and subjected to detached leaf assays and further pathogenicity analysis. A disease symptom rating system was established to account for the various symptoms produced by the different fungal species. Black leaf spots, leaf lesions, stem lesions and leaf discoloration were the most prevalent symptoms observed. Lasiodiplodia pseudotheobromae, Botryosphaeria dothidea, Neofusicoccum parvum, Bipolaris sp., and Diaporthe rhusicola were the top five fungal species with the highest disease rating scores after the five-week period. However, Pestalotiopsis maculans was predicted to be pathogenic over a longer time period. Koch’s postulates confirmed that eleven of the thirteen fungal species were re-isolated after the pathogenicity trial, with the exceptions being Colletotrichum fructicola and the Fusarium solani species complex isolates. Multi-mycotoxin analysis of the seedlings indicated that zearalenone was detected in the Alternaria alternata, F. fujikuroi and F. oxysporum species complex treatments. In conclusion, an unexpectedly large diversity of fungal species was found to be associated with the marama bean in South Africa, several of which have the potential to be pathogenic to the marama bean and produce mycotoxins in vitro and in vivo. Further studies would be required to determine the extent of the pathogenicity of the various fungal species, as well as investigating under what conditions the pathogens would thrive and produce mycotoxins on the plants, thereby identifying future obstacles for marama bean cultivation and commercialisation.
Patterns and drivers of forb diversity in South African grasslands
(University of Pretoria, 2022) Greve, Michelle; Lehmann, Caroline Elizabeth; u16046006@tuks.co.za; Myburgh, Annerine
Biodiversity forms the basis of ecosystem functioning, which forms the foundation of ecosystem services. Quantifying diversity patterns and its drivers is needed to effectively conserve and maintain ecosystems. Diversity is scale-dependent and can be measured as richness at a local scale (alpha-diversity), compositional dissimilarity among sites (beta-diversity) and the accumulation of these two components as diversity across a landscape (gamma-diversity). The effect of the spatial scale of sampling on alpha- and beta-diversity patterns in the same highly diverse ecosystem has rarely been assessed. South African grasslands are both diverse and understudied, providing an ideal location to assess diversity patterns, its drivers, and how spatial scale impacts these. Despite being a grassland, the diversity of this biome is ascribed to herbaceous forb species, even though the majority of the biomass is comprised of grasses. The first aim of this dissertation was to assess patterns of forb alpha- and beta-diversity at species-, genus-, and family-level and the drivers thereof. The second aim was to assess the effect of spatial scale on the species-level diversity patterns and drivers. Forty-two grassland sites were sampled and the species, genus, and family alpha- and beta-diversity, calculated. A total of 487 species, belonging to 146 genera and 49 families were recorded. Beta-diversity was also examined at each taxonomic level via the use of the Jaccard distance index with the dissimilarity at species, genus and family level being 89.52 ± 5.93 %, 79.14 ± 8.82 % and 65.54 ± 9.85% respectively. Spatial grain had a pronounced effect on the non-parametric interpolation of gamma-diversity. Large grain alpha-diversity significantly increased with slope and certain soil and geology types and decreased with an increase in the degree of northness. Intermediate grain alpha-diversity was also significantly higher on certain soil types and textures. Small grain alpha-diversity significantly increased with longer fire return intervals and decreased with higher grazing pressure. The mean beta-diversity at large, intermediate and small grains were 89.52 ± 5.93 %, 94.42 ± 5.12 % and 97.34 ± 5.49 % respectively. Turnover was the most important component of beta-diversity at all spatial grains. Geographic distance and the difference in the degree of northness between sites significantly increased beta-diversity across all spatial grains. In addition to this, the presence of the vertisol soil type and the difference in the days since the last fire increased beta-diversity at large, and intermediate grains respectively. Little variation in beta-diversity was explained at a small grain. The high levels of diversity of the South African grassland biome across all taxonomic levels was demonstrated by this study. Grassland sites were not only very species rich but demonstrated high compositional turnover, which indicated that unique suites of species can be found in different regions. The pronounced effect of spatial scale on the patterns and drivers of diversity became apparent. Therefore, taking spatial scale and environmental gradients into account when making decisions with regards to systematic conservation planning or environmental impact assessments is critical, especially in highly diverse systems, such as the grassland biome. This will ensure the effective conservation of these systems and the associated ecosystem services.
A bioactivity guided study on the anti-gonococcal and anti-inflammatory activity of Ficus abutilifolia stem bark extracts
(University of Pretoria, 2022) Tshikalange, T.E. (Thilivhali Emmanuel); Bapela, Mahwahwatse Johanna; leshayedomingo@gmail.com; Domingo, Leshaye Cynthia Theresia
Background: With high annual infection rates and rapidly increasing antimicrobial resistance (AMR), Neisseria gonorrhoea has become a major global public health concern, especially because delayed treatment often results in severe reproductive complications, and increases the risk of contracting the human immunodeficiency virus (HIV). Aims of the Study: In South Africa, traditional healers use the stem bark of Ficus abutilifolia (Miq.) Miq. to manage gonorrhoea and to treat associated inflammatory conditions. Therefore, this study aimed to evaluate the anti-gonococcal and anti-inflammatory potential of extracts obtained from the stem bark of F. abutilifolia. Materials and Methods: The chemical constituents of the stem bark were extracted in dichloromethane, absolute methanol, 50% methanol (methanol: water, 1:1, v/v) and water, to yield four crude extracts. The anti-gonococcal potential of the crude extracts was determined using the in vitro broth microdilution assay, whilst the anti-inflammatory potential was determined by screening for inhibitory activity against 15-lipoxygenase (15-LOX). Active extracts were subjected to bioassay-guided fractionation and phytochemical analysis using proton nuclear magnetic resonance (1H-NMR) spectroscopy and gas chromatography time-of-flight mass spectrometry (GC-ToF-MS), to determine the compounds or classes of compounds responsible for the observed bioactivity. Results: The polar crude extracts (absolute methanol, 50% methanol, water) all displayed good anti-gonococcal activity, with a minimum inhibitory concentration (MIC) value of 0.20 mg/mL. Low IC50 values comparable to that of quercetin (15.13 ± 0.19 μg/mL) were also reported for these extracts (absolute v methanol: 18.33 ± 0.70 μg/mL; 50% methanol: 23.82 ± 0.90 μg/mL; decoction: 25.58 ± 0.41 μg/mL), thus indicating significant anti-inflammatory potential. 1H-NMR-based metabolomics revealed distinct chemical differences between the active and non-active fractions on the PCA, OPLS-DA and contribution plots, with bioactivity attributable to prominent peaks in the alcohol, vinylic, aromatic, phenolic and amide regions. GC-ToF-MS analysis was also used to tentatively identify compounds present in the active fractions, however, due to the low mass spectral similarity caused by the polar nature of these fractions, the identity of these compounds could not be established with certainty. Conclusion: The results obtained in this study support the traditional use of F. abutilifolia. As this is the first report of anti-gonococcal activity in F. abutilifolia, the results may also help to discover new classes of compounds for the treatment of gonorrhoea and/or associated inflammatory conditions.
Bioactivity and 1H NMR-based metabolomics analysis of polyherbal formulations used traditionally for the treatment and management of sexually transmitted infections
(University of Pretoria, 2022) Tshikalange, T.E. (Thilivhali Emmanuel); Bapela, Mahwahwatse Johanna; u14064635@tuks.co.za; Baba, Urvishi
Ethnopharmacological relevance: Sexually transmitted diseases (STDs) is a major global concern of an ever-growing population. The daily rate of infectious STDs increases by an estimate of one million infections. The development of antimicrobial resistance pathogens is a further concern. Complementary and alternative medicines (CAM) is investigated to provide aid/relief from this resistance. Medicinal plants are used traditionally as an alternative form of medicine. Aim: The aim of this study was to evaluate four medicinal plants (Dicoma anomala sbsp anomala, Elephantorrhiza elephantina, Eucalyptus cinerea and Kigelia africana) used in combination and individually for their antimicrobial activity against sexually transmitted diseases and to determine the similarities of these combinations based on their chemical constituents. Furthermore, the study determined the cytotoxicity effects and mycotoxin presence of the most active extracts. Methodology: Aqueous extracts of various different combinations and individual plant were prepared, and stored at various conditions (includes: temperatures of 4˚C, 25˚C and 37˚C for 7 and 14 days respectively). The extracts were evaluated for their antimicrobial properties against a bacterium Neisseria gonorrhoea and a fungus Candida albicans using the microtiter dilution assay. The fractional inhibitory concentration index of the combinations was also determined against both pathogens. The chemical profile of these samples was analysed using a metabolomic approach via nuclear magnetic resonance and liquid-chromatography mass spectrometry methods (1H NMR and LC-MS). Cytotoxicity studies were conducted to determine the level of toxicity of noteworthy samples against non-cancerous Vero cell lines. Furthermore, various mycotoxin levels present were determined via high-performance liquid chromatography. Results: Antimicrobial activity of polyherbal formulations containing four individual plants (Dicoma anomala sbsp anomala Elephantorrhiza elephantina, Eucalyptus cinerea and Kigelia africana) in combination, which were stored at 25˚C for 7 and 14 days respectively, exhibited noteworthy activity against N. gonorrhoea. Eight of the ninety-eight extracts displayed a minimum inhibitory concentration (MIC) value of 0.39 mg/mL. 1H NMR metabolomic analysis of all the combinations and individual plants exhibited prominent signal peaks in the aliphatic region (0.8- 3.00 ppm), carbohydrate region (3.00- 6.00 ppm) and some combinations yield signals within the aromatic region (5.00- 9.00 ppm). Thus, resulting in a similarity between phytoconstituent amongst the various different combinations irrespective of their storage conditions and antimicrobial activity. The similarity within the different types of combinations is displayed via distinct grouping on the PCA and OPLS-DA score plots. Concerning cytotoxicity studies eight polyherbal formulations were tested, cytotoxicity levels against non-cancerous Vero cell lines ranged from slightly cytotoxic to non-cytotoxic (289.12 ± 21.23 µg/mL to 866.47 ± 22.41 µg/mL). Polyherbal formulations subjected to mycotoxin analysis displayed non-detectable mycotoxin levels. Conclusion: The biological and chemical activity observed amongst the different plant combinations supports the traditional usage of polyherbal formulations in the treatment and management of sexually transmitted diseases.
The physiological effects of heat stress on anthesis and pollination in domesticated sunflowers (Helianthus annuus L.)
(University of Pretoria, 2022) Creux, Nicole; Fourie, Gerda; uyabongeka.memela@up.ac.za; Memela, Uyabongeka
Anthesis and pollination are precisely timed events, which change with the surrounding environment depending on light, temperature, and humidity. Plants and pollinators may exhibit mismatched behaviors as a result of temperature changes, and relatively little information exists about how heat stress and heat waves affect anthesis and pollination in sunflowers (Helianthus Annuus L.). This study investigates the effect of heat stress on timing of pollen emergence, style elongation rate, pollinator visits, pollen viability and stigma receptivity. We sampled during the anthesis period in a field setting under different summer conditions, including sunny and overcast days each with artificially heated and unheated plants; and a natural heatwave. Sunflower insect visits were video imaged in all test conditions, and individual insects were counted. A variety of staining and imaging techniques were used to determine pollen fertility, style elongation, and stigma receptivity. Heating sunflower capitula to approximately 10°C above the natural temperature resulted in a faster rate of style elongation, earlier pollen emergence and reduced stigma receptivity. In both the sunny and overcast days, time-lapse images showed that pollen emergence was 15 minutes earlier on heated plants than unheated ones. Heatwaves, however, bring in significantly more early morning visitors than unheated sunny, which was not observed by artificial heating. At temperatures of 40°C on sunny days, stigma receptivity and pollen fertility appears to significantly decrease over time. Sunflowers are considered a robust and temperature hardy plant, which maintains yields even when subjected to harsh conditions. This is one of the first studies to assess the effect of heat stress on sunflower anthesis. Our findings suggest that even though sunflower anthesis and pollination can be negatively affected by the high temperatures associated with heatwave events, it is able to adapt and manage stress by changing timing of pollen emergence and insects visits to earlier in the day before the high temperatures can have their detrimental effect.
Growth performance and changes in the leaf metabolite profile of Moringa oleifera Lam. cultivars grown in an open hydroponic system and harvested at different Frequencies
(University of Pretoria, 2022-06) Du Toit, Elsie Sophia; Prinsloo, Gerhard; u16398212@tuks.co.za; Managa, Lavhelesani Rodney
Moringa oleifera Lam. is an important plant species with various uses and applications, being cultivated across the world, with most of the production in Africa and Asia. Among other uses, moringa tree is useful for human and animal nutrition, health, cosmetics, biogas and water purification. The tree is associated with important biological activities, due to presence of various flavonoids, flavonol glycosides, glucosinolates, isothiocynates, phenolic acids, terpenes, sterols, and alkaloids compounds. However, the composition and concentration of bioactive compounds in plants, could be affected by factors such as the growing environment, harvesting practices, climatic factors, etc. The aim of this study was therefore to determine changes in the leaf metabolite profile of three M. oleifera genotypes, namely PKM-1, Indian conventional hybrid and Malawi hybrid due to cultivation systems, harvesting frequencies, harvesting time, seasonal changes and genotypes. Trees of these cultivars were grown in an open hydroponic structure and in the field and leaf material were collected throughout the growing season from October to May. Proton nuclear magnetic resonance (1H-NMR) was used for data acquisition, and multivariate data analysis by means of principal component analysis (PCA), partial least square discriminatory analysis (PLS-DA), and orthogonal partial least square discriminatory analysis (OPLS-DA) were applied to determine the changes in the leaf metabolite profile, and also to identify the spectral features contributing to the separation of samples. Targeted metabolite analysis was used to match the NMR peaks of the compounds with the NMR chemical shifts of the contribution plot. The difference in concentration of the compounds were statistically determined comparing the concentrations of the compounds in the different samples. The results showed differences in the leaf metabolite profile due to effect of cultivation systems, harvesting frequencies, harvesting time, genotypes, and changes in growing seasons. Among the compounds that were affected, were chlorogenic acid, ferulic acid, vanillic acid, wogonin, niazirin, esculetin and gamma-Aminobutyric acid. All these compounds showed an increase in concentration under “low” and “intermediate” harvesting frequencies as compared to “high” harvesting frequency. The concentration level of these targeted compounds was also affected by cultivation system, harvesting time, and by genotypes. These results provide insight into the effect of harvesting frequencies, harvesting time, cultivation system and genotypes on the metabolite profile and associated medicinal activity of M. oleifera leaf materials.

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