Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The Mountain Fynbos biome, a division of the Cape Floristic Region (CFR), is
home to round-leafed Buchu [Agathosma betulina (Berg.) Pillans], one of South
Africa’s best-known endangered herbal medicinal plants. Agathosma betulina is
renowned as a traditional additive to brandy or tea, which is used for the
treatment of a myriad of ailments. In its natural habitat, A. betulina thrives on
mountain slopes in acid and highly leached gravelly soils, with a low base
saturation and low concentrations of organic matter. To adapt to such adverse
conditions, these plants have formed mutualistic symbioses with arbuscular
mycorrhizal (AM) fungi. In this study, the effect of indigenous AM taxa on the
physiology of A. betulina is investigated. In addition, the AM taxa responsible for
these physiological responses in the plant were identified using morphological
and molecular techniques.
Agathosma betulina was grown under glasshouse conditions in its native
rhizosphere soil containing a mixed population of AM fungi. Control plants,
grown in the absence of AM fungi, were included in the experimentation. In a
time-course study, relative growth rate (RGR), phosphorus (P)-uptake, P
utilization cost, and carbon (C)-economy of the AM symbiosis were calculated.
The data showed that the initial stages of growth were characterized by a
progressive increase in AM colonization. This resulted in an enhanced P-uptake
in relation to non-AM plants once the symbiosis was established. Consequently,
the lower P utilization cost in AM plants indicated that these plants were more efficient in acquiring P than non-AM plants. When colonization levels peaked,
AM plants had consistently higher growth respiration. This indicated that the
symbiosis was resulting in a C-cost to the host plant, characterized by a lower
RGR in AM plants compared to non-AM plants. Arbuscular mycorrhizal
colonization decreased with increasing plant age that coincided with a decline in
P-uptake and growth respiration, along with increases in RGR to a level equal to
non-AM plants. Consequently, the AM benefit was only observed during the
initial stages of growth. In order to identify the AM fungi in planta, morphological
and molecular techniques were employed, which indicated colonization by AM
fungi belonging to the genera Acaulospora and Glomus. Phylogenetic analyses
of a dataset containing aligned 5.8S ribosomal RNA gene sequences from all
families within the Glomeromycota, including sequences obtained during the
study, supported the above mentioned identification. / AFRIKAANSE OPSOMMING: Die Fynbos bergbioom, ‘n onderafdeling van die Kaapse Floristiese Streek,
huisves rondeblaar Boegoe [Agathosma betulina (Berg.) Pillans], een van Suid
Afrika se bekendste bedreigde medisinale plante. Agathosma betulina is bekend
vir sy gebruik as tinktuur vir die behandeling van verskeie kwale. Die plant kom
voor in bergagtige streke, in suur en mineraal-arm grond, met ‘n lae organiese
inhoud. Gevolglik, om aan te pas by hierdie ongunstige kondisies, vorm die
plante simbiotiese assosiasies met blaasagtige, struikvormige mikorrisa (BSM).
In die huidige studie is die effek van hierdie BSM op die fisiologie van A. betulina
ondersoek. Die identiteit van die BSM is ook gevolglik met morfologiese en
molekulêre identifikasie tegnieke bepaal.
Agathosma betulina plante is onder glashuis kondisies in hul natuurlike grond
gekweek, wat ‘n natuurlike populasie van BSM bevat het. Kontroles is ook in die
eksperiment ingesluit en hierdie stel plante is met geen BSM geïnokuleer nie.
Gevolglik is die relatiewe groeitempo, fosfor opname, fosfor verbuikerskoste
asook die koolstof ekonomie van die plante bereken. Die data het getoon dat die
eerste groeifase gekarakteriseer is deur toenames in BSM kolonisasie vlakke.
Dit het tot ‘n hoër fosfor opname in BSM geïnokuleerde plante gelei. Die laer
fosfor verbuikerskoste gedurende hierdie fase het aangedui dat die plante wat
geïnokuleer is met BSM oor beter meganismes beskik het om fosfor uit die grond
te bekom. Toe BSM kolonisasie vlakke gepiek het, was groei respirasie hoër in
BSM geïnokuleerde plante as in die kontroles. Dit het aangedui dat die BSM kolonisasie van plante tot hoër koolstof kostes vir hierdie plante gelei het, wat
weerspieël is in die laer groeitempo van die BSM geïnokuleerde plante. Die
BSM kolonisasie vlakke het gedaal met toenemende ouderdom van hul gasheer
plante, wat gekarakteriseer is deur ‘n laer opname van fosfor en laer groei
respirasie, tesame met ‘n toename in relatiewe groeitempo tot vlakke soortgelyk
aan die van die kontrole plante. Die BSM voordele vir die plant is dus net
gedurende die eerste groeifase waargeneem. Die BSM wat verantwoordelik is
vir hierdie fisiologiese veranderinge is gevolglik geïdentifiseer met behulp van
morfologiese en molekulêre tegnieke en dit is gevind dat BSM wat behoort tot die
genera Acaulospora en Glomus binne hierdie plante voorkom. Filogenetiese
analise gegrond op opgelynde 5.8S ribosomale RNA geen volgordes afkomstig
van al die families binne Glomeromycota asook volgordes gevind in die studie,
het die bogenoemde identifikasie gestaaf.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16600 |
| Date | 10 1900 |
| Creators | Cloete, Karen Jacqueline |
| Contributors | Botha, A., Valentine, A.J., University of Stellenbosch. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xiii, 126 leaves : ill. |
| Rights | University of Stellenbosch |
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