Impact of spatial variation and extraction solvents on bioactive compounds, secondary metabolites and antifungal efficacy of South African Impepho [Helichrysum odoratissimum (L.) Sweet

Abstract

Extracts of indigenous plants have been explored to control several plant diseases and fruit pathogens, as well as in the development of bioactive compounds. This study investigated the impact of spatial variation and application of different extraction solvent on the antioxidant properties (total polyphenols (TP), and radical scavenging capacity via 2,2-diphenyl-1-picrylhydrazyl (DPPH)), secondary metabolite profile and the inhibitory activity (against Botrytis cinerea) of South African Impepho (Helichrysum odoratissimum L.). Fresh H. odoratissimum were harvested from two different agro-climatic sites of South Africa: Western Cape (WC) and Kwazulu Natal (KZN) provinces. Crude extracts were obtained using 95% ethanol and 70% acetone. Rovral® WP was used as control in antifungal study. Secondary metabolites of these extracts were relatively quantified using gas chromatography-mass spectroscopy (GC-MS). Extracts obtained via acetone had the highest soluble solids (SS), TP and DPPH capacity, for H. odoratissimum from WC and KZN (p ≤ 0.05). All extracts of H. odoratissimum provided considerable inhibition against B. cinerea in comparison to the controls. A total of 18 chemical classes of secondary metabolite were identified across all samples. Sesquiterpenoids were found to be the most relatively abundant class of compounds (31%–40%), followed by sesquiterpenes (9%–40%) and alkanes (7%–12%). Acetone extract of H. odoratissimum from KZN had the highest relative amount of sesquiterpenes. Higher relative abundance in viridiflorol (26% and 16.8% for acetone and ethanol extracts, respectively), were obtained for samples collected from WC compared to KZN province (p ≤ 0.05).