Effect of pH on growth, mineral content and essential oil quality of buchu (<i>Agathosma betulina</i>) grown under controlled conditions

Abstract

Buchu (Agathosma betulina) is a traditional medicinal plant in the Western Cape province of South Africa and the essential oil derived from the leaves is exported in large volumes. The essential oil is not only used for medicinal purposes, but also as a flavour enhancer in the food industry. Agathosma betulina seedlings were transplanted into 9.5 l pots filled with a 1:1 mixture of graded, washed sand and coco peat. Five pH treatments (3–3.99, 4–4.99, 5–5.99, 6–6.99 and 7–7.99), replicated eight times, were applied using a hydroponic system to determine the optimum pH (H₂O) range for the production of high-yielding buchu with acceptable essential oil quality. Plant height displayed an exponential increase over time, but plants in the pH 7–7.99 treatment grew less vigorously compared to other treatments. Biomass production was higher in the pH 4–4.99 treatment. High levels of diosphenol and absence of any measurable amounts of cis- and trans-acetylthio-p-menthan-3-one isomers were obtained in the oil analyses from all pH treatments, which indicated that the oil originated from pure A. betulina.

Keywords: Agathosma betulina, biomass yield, essential oil, pH variation

South African Journal of Plant and Soil 2013, 30(2): 107–112