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Stellenbosch University (2022)

Fungal endophyte assemblages associated with twigs of olives in the Core Cape Subregion, South Africa

Ngubane, Nombuso Portia

Titre : Fungal endophyte assemblages associated with twigs of olives in the Core Cape Subregion, South Africa

Auteur : Ngubane, Nombuso Portia

Université de soutenance : Stellenbosch University

Grade : Doctor of Philosophy (PhDConsEcol) 2022

Résumé partiel
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.

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