Propagation of Coleonema album (Thunb.) Bartl. & J. C. Wendl. : a horticultural and medicinal plant.

Abstract

Coleonema album is a South African green treasure, endemic to the Cape region and hard to find in other parts of the country. It is ranked among the most highly utilized medicinal plants at present. The plant extracts exhibit a wide range of pharmacological activities due to its bioactive compounds. Immunat, a tincture from this plant is marketed commercially. Medicinal plant gatherers are on the lookout for this plant due to its high demand and market price. Several natural product companies in South Africa are now exporting Coleonema album oil. Its showy beautiful white flowers make it a valuable ornamental plant. There is no accredited germination protocol available for this medicinal and ornamental plant till date. In this study, the chemical and environmental conditions required for optimum seed germination and seedling growth were studied. The effect of light, temperature shifts, cold and warm stratifications, smoke-water, butenolide, pH levels, plant growth regulators (kinetin, 6-benzyladenine, indole acetic acid and α-Naphthalene acetic acid), salt solutions (sodium chloride and ammonium nitrate) on seed germination were investigated. Seeds showed favourable response of germination at low temperatures (10 and 15 ºC). Seeds exposed to continuous darkness at low temperatures showed highest germination at 15 ºC. Temperature shift (from 20 ºC to 15 ºC) favoured seed germination. pH 6 is the most conducive pH level for Coleonema album seed germination (52.5%). Sodium chloride and ammonium nitrate solutions (pretreatment for 2 weeks) significantly improved germination at a 10-2 M concentration with 62.5 and 75% germination respectively. Coleonema album seeds exhibit a temperature-dependent physiological dormancy. Seed germination of this plant is quite erratic as seed germination started 21 days after incubation and lasted for over 90 days. Germination rate of the seeds is too slow to meet the local and international demand for this plant. Plant tissue culture techniques have been used as an alternative for mass cultivation of plants that are difficult to propagate from seeds. Therefore, an effective micropropagation protocol was developed as a measure to conserve this highly utilized medicinal plant. The effects of the cytokinins: BA, kinetin, TDZ and topolins on in vitro shoot formation of Coleonema album were investigated. Of all the cytokinins tested, 5 μM mT gave the highest number of shoots (14.50) per explant. Combination of 5 μM mT with various concentrations of IBA and NAA significantly increased shoot production. Shoots cultured on IBA supplemented medium produced roots. Root production from NAA cultures is unfavourable as most of the shoots developed callus at the base of the stem. The result of this study has shown that mT has potential as a highly active alternative to BA and other cytokinins for Coleonema album in vitro shoot production. Over 1,000,000 plantlets could be produced annually using the in vitro propagation protocol developed in this study. The results of this study will be useful as a guide for mass cultivation of this ornamental and medicinal plant. It will also provide an opportunity for propagation of Coleonema album in other parts of the country. By virtue of this, the pressure on the wild population of this species could be greatly reduced.