Within the Department there is a strong research interest in the micropropagation (mass production by tissue culture) of selected crops (e.g. cassava) and of South African indigenous plants. Particular emphasis is placed on the mass production of plants via the developmental process known as ?somatic embryogenesis?. The somatic embryos that are produced are used in both genetic transformation and cryopreservation studies.
Genetic transformation involves the insertion of new genes into the plant tissues using the microorganism Agrobacterium. Cryopreservation is the storage of tissues at temperatures below -70 oC and is an ideal method for the long-term conservation of South Africa s plant genetic resources.
Staff interested in this research area:
Dr David Mycock
Dr Vincent Gray
Postgraduate students
JONATHAN GROLL(PhD) Supervisors: Dr Dave Mycock and Dr Vincent Gray
The induction, proliferation and maturation of somatic embryos of cassava (Manihot esculenta Crantz.)
In Africa, the starch stored in the tubers of cassava provides a staple food for over 200 million people. Although not extensively grown in South Africa there is renewed interest in the cultivation of this species as a source of starch for the paper industry. A multi-step approach, whereby each of the stages of somatic embryogenesis is independently optimised was used to produce an improved protocol for cassava somatic mbryogenesis. A novel approach was used to produce a highly embryogenic callus tissue without extensive selection for embryogenically competent material. The embryos produced by such a method were exposed to a controlled desiccation treatment above a saturated salt solution in order to further optimise and improve cassava germination.
In vitro storage of Zea mays L. by cryopreservation
Maize is one of the most important crops grown by humans, however due to the extensive development of hybrids original germplasm is being lost. Consequently it has become necessary to develop effective preservation procedures to ensure the availability of useful germplasm at any time. Cryopreservation is the non-lethal storage of biological tissue at ultra-low temperatures (usually - 196 oC). The chief advantage of storing biological material at such low temperatures is that both metabolic processes and biological deterioration are slowed considerably or even halted. Cryopreservation comprises many steps, of which freezing is only one. Successful recovery is dependent on the combined effects of cryogenics and pre- and post-freeze treatments. This project is investigating the pre- and post-cryostorage procedures for a local maize variety.
SANDRA LAMINSKI(PhD) Supervisors: Dr Vincent Gray and Dr Robbie Robinson
Molecular characterization and transformation in South African cassava (Manihot esculenta Crantz.)
The project uses a number of molecular techniques to characterize a group of elite South African cassava cultivars. RAPDS and isozymes were included here. Two reporter genes, GUS and GFP were inserted into the genomes of selected cassava cultivars using Agrobacterium tumifaciens.
Somatic embryogenesis from Blesbok sweet potato (Ipomoea batatas L.) tubers
The protocol for sweet potato somatic embryogenesis from tuber explants, developed by Newell et al.(1995), was modified for the elite South African cultivar, Blesbok. Disk explants were left for four weeks on medium containing a range of 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin concentrations. Explants were then transferred to medium containing 1 mg/l 1-napthalene acetic acid (N ) and 0.1 mg/l 6-benzylaminopurine (BAP). Greening and subsequent abnormal root development occurred in the absence of 2,4-D. Somatic embryogenesis was observed at 2,4-D concentrations of 0.1 ans 0.5 mg/l. Browning was observed at all 2,4-d concentrations higher than 0.5 mg/l. This is the first account of the successful induction of somatic embryogenesis using Blesbok sweet potato tubers.
Supervisors: Dr Dave Mycock (University of the Witwatersrand) and Dr M.P.Watt (University of Natal - Durban)
The development of medium and long-term storage protocols for Eucalyptus grandis
Eucalyptus trees are of great economic importance, providing fuelwood, timber and raw materials for the paper and pulp industry. Consequently, the demand for Eucalyptus wood is steadily increasing as the human population increases. In order to meet this demand, rapid advances in tree improvement and breeding techniques to produce clones with shorter rotation times and superior quality wood are necessary. However, successful breeding requires a broad genetic base. Therefore the integration of genetic conservation into tree improvement and tree breeding strategies is essential. In situ conservation strategies are not suitable for the conservation of forest species due to the unavailability of suitable land for conservation stands. Ex situ strategies, involving the use of in vitro techniques such as minimal growth storage and cryopreservation are therefore required. Hence the aim of this project is to establish protocols using these techniques for medium and long-term storage of E. grandis, one of the most important commercial tree species in South Africa.
The in vitro storage of cassava (Manihot esculenta Crantz)
This project aims at achieving genetic resource conservation as well as improving practical storage aspects for cassava tissue. A micropropagatory procedure will be utilized in order to supply a range of in vitro material which will be stored in two ways: Long-term storage will be in the form of cryopreservation and medium-term storage in the form of encapsulation. Ultrastructural as well as water content and viability determinations will be used to monitor the tissue response to these processes.
