Nitrogen application influences quality,pharmacological activities and metabolite profiles of Athrixia phylicoides DC. (Bush tea) cultivated under greenhouse and field conditions

Bush tea (Athrixia phylicoides DC.) is a popular aromatic plant, indigenous to South Africa. For many decades, indigenous people have widely consumed the tea as a healthy beverage and a medicine. The objective of the study was to investigate the influence of nitrogen fertiliser application on the quality, pharmacological activities and metabolite profiles of the leaves and twigs of bush tea cultivated under greenhouse and field conditions. Treatments consisted of 0, 75, 150, 225, 300 and 375?kg/ha N, arranged in a randomised complete block design with five replicates. Parameters measured were leaf tissue nitrogen, total polyphenols, total flavonoids, total tannins, total antioxidants, antimicrobial activity and cytotoxicity. In addition, metabolites were identified and measured using gas chromatography linked to mass spectrometry (GC-MS) and liquid chromatography linked to mass spectrometry (LC-MS). The results of this study showed a significant quadratic response of total polyphenols, total flavonoids, total tannins and total antioxidants of bush tea leaves and twigs, irrespective of the growth environment ranging from 150 to 225?kg/ha N. The results further suggested that, despite the growing environment, nitrogen treatments did not improve the minimum inhibition concentration and minimum microbicide concentration of bush tea with extract concentrations ranging from 25.0 to 3.1?mg/g. Bush tea was found to be non-toxic (IC₅₀ above 100) under both growing conditions, irrespective of nitrogen treatments. Despite trials being conducted under greenhouse and field conditions and with different nitrogen treatments, there were no distinct differences regarding the gas chromatography linked to mass spectrometry and liquid chromatography linked to mass spectrometry compounds. The future aims of the study are to investigate the effects of nitrogen fertilisation, the timing of nitrogen fertilisation and the planting density on the yield, quality, plant metabolites and pharmacological activity of field-grown bush tea.