Abstract
Background: Salvia dolomitica Codd. and Salvia namaensis Schinz. are indigenous to southern Africa and are used as medicinal plants in folk medicine.Aim: This study aimed to assess the effects of different levels of water deficit treatments on the growth, concentration of secondary metabolites, and anti-Fusarium oxysporum activity of S. dolomitica and S. namaensis.Setting: Experiments were carried out on the Bellville campus of the Cape Peninsula University of Technology, Cape Town.Methods: Four weeks old seedlings of the two species were subjected to 3-, 6-, 9- and 12-day water deficit regimes. Secondary metabolites such as polyphenols, alkaloids, and flavanols were assessed using spectroscopic methods. The anti-fungal activities of crude extracts obtained from plants were evaluated in a micro-dilution bioassay.Results: In all treatments, the plant height, crown width, number of stems and leaves, and fresh and dry weights reduced with increased water deficits. Acetone extracts from all treatments showed anti-fungal activity. However, extracts from the treatment with moderate water deficit (6-day watering interval) recorded significantly (P 0.01) better inhibition of F. oxysporum at the 18 h post incubation than the commercial fungicide, Mancozeb.Conclusion: This research has revealed that mild to moderate water deficit level favours the accumulation of alkaloids in S. dolomitica. Meanwhile, mild to severe water deficit significantly lowered flavanol content in S. namaensis. There was a correlation between the increase in total alkaloid contents and the enhanced anti-fungal activity of extracts of S. dolomitica. The present findings pave the way for optimised cultivation of medicinal plants and development of bioactive natural products.
Highlights
South Africa is ranked as the 30th driest country globally (World Resources Institute 2015)
The trays of cuttings were placed on hotbeds maintained at a temperature of 26.5 °C under intermittent mist in the production glasshouse with controlled environmental conditions (22 °C; 100% Relative humidity (RH)) until the roots appeared through the drainage holes of the trays
This study indicates that moderate water deficits increased the flavanol content of S. dolomitica extracts, and mild and severe water deficit treatments decreased the flavanols’ levels
Summary
South Africa is ranked as the 30th driest country globally (World Resources Institute 2015). South Africa is a water-scarce country (Goldin 2010; Muller et al 2009), it is home to 6% of the world’s plant diversity (Raimondo 2015), and has one of the richest temperate flora globally (Staden & Lotter 2015). South Africa has many indigenous medicinal species that have the prospects of becoming sources of natural pesticides. The global demand for natural products is increasing as the world becomes more conscious of synthetic products’ negative impacts on human and environmental health (Saha, Dasgupta & Saha 2005). Salvia dolomitica Codd. and Salvia namaensis Schinz. are indigenous to southern Africa and are used as medicinal plants in folk medicine
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