Micropropagation of P. cynaroides L.

Abstract

The exotic blooms of the indigenous South African flowering plants and the biodiversity of the floral material available, have led to a high demand for these flowers on the international market. A wide variety of high-quality flowers, of which Protea cynaroides L. is an important component, are exported from South Africa. However, because of the high demand for the export market the producers are unable to supply enough plant material. Therefore, due to the limited supply, poorer quality flowers are exported which results in lower prices obtained. One of the reasons for the lack of flowers available for export is that being a woody perennial, P. cynaroides require a longer period of time to grow when conventional propagation methods are used. Micro propagation of P. cynaroides may become the most suitable alternative propagation method for rapid production and to ensure high standards of quality. In this study, Stage I (establishment) and Stage 2 (multiplication) of micro propagation were investigated. Establishment (Stage I) of the explants was achieved by using Murashige and Skoog medium with the addition of 30 mg.1-1 GA3. However, it was found that browning of the explant tissues caused by phenolic oxidation was a major problem during the establishment stage, as the browning of many explants led to the inability of the axillary buds to sprout which resulted in death. Browning of tissues occurs when phenolic compounds are oxidized, this usually happens when the plant tissues are stressed or injured during explant preparations. Therefore, methods to control oxidation were tested in an experiment which included the use of sterilants (mercuric chloride and sodium hypochlorite) and antioxidants (ascorbic and citric acid). The selection of a few treatments which showed potential in controlling oxidation, followed by further tests, led to positive results. Phenolic oxidation was reduced by stirring the explants in 100 mg.1-1 ascorbic acid and 1500 mg.1-1 citric acid for 1 hour. This was followed by growing the explants in a 16-hour photoperiod which was suitable for the axillary buds to sprout. Subsequently, Stage 2 of micropropagation (multiplication) was successfully done by subculturing the explants from the establishment stage onto the multiplication media. The effects of phosphorous on the growth of the explants were tested by using two media, where no ammonium phosphate was added into one medium, while 1400 mg.1-1 ammonia phosphate was added to the other. Surprising results were obtained when explants in both media grew well, illustrating that P. cynaroides may be tolerant to high levels of phosphorous. However, a possible reason for this is that because no roots were formed by the explants in the multiplication medium, the phosphorous in the medium were not taken up by the explants. These results also illustrated that two-budded explants achieved a higher survival rate and longer mean length than one-budded explants. Investigation into the rooting requirements of the explants, Stage 3 (rooting) of micropropagation must still be achieved.