Germination and seedling growth requirements for propagation of Dioscorea dregeana (Kunth) Dur. and Schinz — A tuberous medicinal plant

Intensive collection of underground tubers of the medicinal plant Dioscorea dregeana from indigenous forests is a threat to the wild population. Domestication of this plant is the only possible alternative to fulfill the demand of formal and informal medicinal markets in South Africa. This study reports fundamental requirements for seed germination and seedling growth of D. dregeana. Germination responses of seeds were tested at different temperature regimes, light conditions and smoke treatments. The highest percentage germination (≥ 95%) and mean germination time (MGT) of 10 days was at 30/15 °C, followed by 25 °C. No germination was observed at 10 °C. Different light conditions did not significantly affect percentage germination at 25 °C; however, under constant dark conditions the MGT was reduced. Smoke-water (1:500 v/v) and a butenolide (10− 7 M), isolated from smoke, stimulated germination and improved seedling vigour. Seedling growth was best at 25 °C and 30/15 °C, with large underground tubers forming on all seedlings. This indicates that temperature plays a significant role in regulating growth of tubers. Seedlings watered once a week with half-strength Hoagland's nutrient solution showed best growth performance, whereas, a deficiency of either nitrogen, phosphorous or potassium negatively affected seedling growth. Thus, we recommend application of moderate fertilizers and watering once per week at 25 °C for raising healthy D. dregeana seedlings.