Browsing by Author "Ngubane, Nombuso Portia"
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- ItemFungal endophyte assemblages associated with twigs of olives in the Core Cape Subregion, South Africa(Stellenbosch : Stellenbosch University, 2022-04) Ngubane, Nombuso Portia; Roets, Francois; Dreyer, L. L.; Slippers, Bernard; Kemler, Martin; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Fungal endophytes are increasingly gaining recognition for their role in plant health. In the face of global change and unprecedented biodiversity loss, it has become an urgent concern to understand these valuable microbes. The main objectives of the work presented here were two-fold, 1) to gain better understanding of the fungal endophytes in a threatened biodiversity hotspot and 2) to improve our understanding of fungal endophyte assemblages associated with ecologically and agriculturally important Olea species. The Core Cape Subregion provides a rare and important study area since it is one of the few areas of olive cultivation with close native relatives, including O. europaea subsp. cuspidata. Many olive (O. europaea subsp. europaea) orchards in the Core Cape Subregion are near natural O. europaea subsp. cuspidata populations. In Chapter 2, I investigated the role of host identity and geographic distance on fungal endophyte assemblages associated with the two Olea europaea subspecies in South Africa. Although many taxa were shared between these hosts, the native host harboured significantly higher alpha diversity. The beta diversity of fungal endophytes also differed significantly between hosts. Geographic distances played a significant role in shaping fungal endophyte assemblages of both hosts, more so in the native host. The native O. europaea subsp. cuspidata is a widely distributed plant growing across a variety of habitats that is also a favoured shade plant, planted in gardens, parks and roadsides. In Chapter 3, the response of fungal endophytes to different levels of disturbance (habitat context) and to differences in surrounding vegetation types (vegetation contrast) were assessed. Endophyte species richness was influenced by habitat context and vegetation contrast. However, fungal endophyte assemblage composition was only affected by habitat context. This suggests that although the host can tolerate different habitat context levels, its fungal endophytes are particularly sensitive to even the mildest of disturbances found in the semi-natural habitat context. In the Core Cape Subregion, two additional Olea species (O. capensis and O. exasperata) are native to South Africa. This made it possible to assess the impact of host identity and relatedness on fungal endophyte assemblages of native hosts (Chapter 4). Fungal endophytes were documented in five native hosts (three Olea and two non-Olea hosts) in the Kogelberg Biosphere. Although fungal endophyte assemblages were significantly different between hosts, this was not correlated to host relatedness (phylogeny). Other factors, other than host phylogeny, were more important to fungal endophytes in this area. The lack of a phylogenetic signal reflected in fungal endophyte assemblages of native Oleaceae hosts suggests that the differences in fungal endophyte assemblages between O. europaea susp. europaea and O. europaea susp. cuspidata are likely due to differences in their histories. The differences in planted African olive trees versus those in the natural context, and the differences between the cultivated and the native olives demonstrate the importance of habitat context. The dynamic nature and diversity of fungal endophytes within the investigated hosts highlights the need to improve our understanding of fungal endophytes in South Africa, especially in native hosts.
- ItemPopulation genetics of the Sporothrix splendens complex from Protea L. in South Africa(Stellenbosch : Stellenbosch University, 2017-03) Ngubane, Nombuso Portia; Dreyer, L. L.; Roets, Francois; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Ophiostomatoid fungi consist of a remarkable assemblage of species that are distantly related (Orders Microascales and Ophiostomatales) and that are grouped based on convergent evolution towards arthropod dispersal. Most of these fungi are known as pathogens of trees. An unusual assemblage of species belonging in the genera Knoxdaviesia (Microscales) and Sporothrix (Ophiostomatales) were found within infructescences of Protea species. Thus far three and nine species, respectively have been described from this niche. Although distantly related, these fungi share the same hosts and vectors with some of them more exclusive in their host selection than others. The reasons for preference towards certain hosts and the different levels of exclusivity are unknown, especially in Sporothrix. Also, in contrast to Knoxdaviesia, nothing is known regarding their population genetic structure. In this study we aimed to gain insight into the population genetics of Sporothrix species in the Sporothrix splendens clade. This was done by investigating the population structure of S. africana, S. protearum and S. splendens. In the second chapter the population structure of S. splendens across its entire known distribution range was investigated and compared to its distant relative K. proteae. These fungi share the same host (Protea repens) and vectors (mites and beetles). In the third chapter the aim was to expand on knowledge of the dispersal of Protea-associated ophiostomatoid fungi to include species found in Protea species occurring outside the Core Cape Subregion (CCR). To this end, the population structure of two sister species, S. africana and S. protearum, were investigated in order to ascertain whether gene flow is restricted based on geography or host identity and whether these two similar taxa represented two discrete species. Population genetic structure was assessed using a fast evolving anonymous marker (m128) and the slower evolving beta-tubulin marker. Genetic diversity (haplotype and nucleotide diversity), population differentiation, rates of migration, isolation by distance and the relationship between haplotypes were calculated for both markers. In the case of S. africana and S. protearum, analyses were partitioned to test the effect of geography and that of host identity. The population structure of S. africana, S. protearum and S. splendens were not structured according to geography and, in the case of the former two, neither were they structured according to host identity. These patterns matched those of Knoxdaviesia proteae and K. capensis. Also, much like the Knoxdavesia species from Protea, the Sporothrix species showed high genetic diversity, rates of gene flow and no signal for isolation by distance. In addition, two new species (Sporothrix smangaliso and S. nsini) were discovered in the course of field work and these are described in the forth chapter based on morphology and phylogenetic analyses of data from the ITS, beta-tubulin and calmodulin DNA markers. Results of this study provide strong evidence of convergent evolution between two distantly related fungal genera driven by adaptation to insect dispersal. In addition, they highlight the importance of the role played by long distance dispersers in shaping populations of Sporothrix and Knoxdaviesia within Protea. The discovery of two additional Sporothrix species belonging to two distantly related clades in the genus supports the hypothesis that the Protea niche was independently colonised more than once by members of this genus and that some clades have since experienced radiation such as the S. splendens clade. However, this radiation does not seem to be driven by host relationships or geography, at least for the non-CCR taxa, and warrants further investigation.