Hoodia gordonii has been used by the San people for centuries as an appetite
suppressant while they were on long hunting trips. These succulents are globally known
as an important component in diet supplements and products which assist in weight-loss.
Together with other plants these contribute towards a multimillion US dollar market, as
many pharmaceutical and nutritional companies have made significant financial
investments in the research and development for people who suffer from weight
problems and obesity. In South Africa, H. gordonii is classified as being endangered,
because so many pharmaceutical companies cashed-in on the dietary characteristics of
these succulents. The plant is found in the South Western parts of Southern Africa
mainly in the Karoo, Kalahari and Namib deserts. Plants were also grown in cultivated
nurseries under favourable conditions for commercial use. However, diseases have
dramatically hampered production in nurseries with almost total loss of crop. Although
not many diseases have been documented on this plant, Fusarium wilt, a devastating
fungal disease of H. gordonii, caused by F. oxysporum had been identified. This disease
is not only responsible for economic losses, but also contaminates the soils with spores,
which remain dormant until the next season as inoculum. This study concentrated on the
morphological characterisation and molecular identification of the Fusarium wilt causing
pathogen present in four areas (Kakamas, Klein Pella, Pofadder and Prieska) as well as
the morphological evaluation of the host. Fusarium oxysporum was identified as the
causal agent of Fusarium wilt on H.gordonii plants. The AFLP analysis and DNA
sequences resulted in two distinct groups. Those that clustered in the AFLP cluster B
were also grouped in a TEF cluster B, however some isolates from AFLP cluster A also
grouped together with the TEF cluster B. The low genetic variation revealed by the AFLP
analysis indicated that differences amongst the pathogen isolates occur, but the DNA
sequences confirmed that these isolates share a common ancestor. DNA sequencing
analysis was used to place 44 South African F. oxysporum isolates into the phylogenetic
groups as described by OâDonnell and associates. South African F. oxysporum isolates
clustered into two groups. The observed genetic variation amongst individual isolates
was lower than the genetic variation between out-group isolates. Two clusters were
identified; within each cluster isolates had a relatively high frequency of clones. These
clones confirm that these pathogen isolates share similar allele frequencies. Results from
sequencing data showed that the isolates fall within the FOSC, however there was no
isolates identified that show 100% similarities when compared with all three genes
sequences with recorded genetic sequences of F. oxysporum isolates in other parts of the world. Therefore, based on the current taxonomic system, of host specificity the
fungus only infects H. gordonii, so the study has proved that a possible new formae
specialis has been identified. New preventative measures must be applied to the host
when planting in nurseries. Knowledge gained from analyses of the genetic
fingerprinting, DNA sequencing of these isolates and the mporphological evaluation of
the host might assist with the development of effective control strategies, i.e. resistance
breeding against Fusarium wilt. This will provide an incentive to potential farmers to plant
H. gordonii, thus improving production of this succulent for pharmaceutical companies
and nurseries in South Africa.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-10292014-103553 |
| Date | 29 October 2014 |
| Creators | Philippou, Onoufrios Agathoclis |
| Contributors | Prof WJ Swart, Dr A Minnaar-Ontong, Dr A van Biljon |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-10292014-103553/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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