Measuring and optimising umckalin concentration in wild-harvested and cultivated Pelargonium sidoides (Geraniaceae)

Pelargonium sidoides DC. (Geraniaceae) root extracts are used locally and globally as herbal medicines. Subsequently, high levels of wild root harvest in the years preceding this study, to supply international demand for raw materials, prompted this investigation of the prospects for sustainable root harvest through wild collection and greenhouse cultivation. A novel method was developed for the purification of umckalin, a bioactive constituent in root extracts, such that the root umckalin concentrations of wild and cultivated plants could be quantified by HPLC. A geographical survey of wild plants revealed that root umckalin concentrations were inversely related to the average annual rainfall of the collection site (r2 = 0.43, p < 0.0001) and directly related to soil pH (r2 = 0.46, p < 0.0001). Thus, the possibility of inducing high umckalin concentrations in greenhouse-cultivated plants was investigated by subjecting plants to water stress. This treatment, and those using leaf applied hormones (cytokinin and gibberellin) and root competition with a fast growing annual (Conyza albida), did not significantly affect root umckalin concentrations compared to well-watered controls. However, greenhouse-cultivated control plants showed wild equivalent umckalin concentrations and circa six times greater growth rates than plants in a wild harvest experiment. These results support the ex situ cultivation of roots to supply future market demand.