Characterisation of both Hoodia gordonii and the associating wilt causing pathogen Fusarium oxysporum

English: 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 O’Donnell 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.