Effect of water stress on antimicrobial activity of selected medicinal plant species

Abstract

a b s t r a c t Available online xxxx Edited by J.J.M. MeyerSome traditional medicinal practitioners believe that cultivated medicinal plants will lose healing powers, compared to plants growing in nature. Several scientists have shown that a plant under stress will produce secondary metabolites that may influence its medicinal properties. This perception has negative effects on the cultivation of medicinal plants to control local extinctions by uncontrolled collection of medicinal plants. To investigate this perception we examined the effect of water treatments on the antimicrobial activity of selected plant species grown under controlled conditions. Firstly, Tulbaghia violacea and Hypoxis hemerocallidea plants were subjected to watering regimes of 1000 ml of water in intervals of 3,14 and 21 days in a preliminary experiment. Subsequently, T. violacea, Leonotis dysophylla and Bulbine frutescens were subjected to different water regimes of 50, 100, 200 and 500 ml every second day for 240 days. Air-dried leaves of matured plants were finely ground and extracted with acetone. Minimum inhibitory concentration (MIC) and total activity were determined in order to evaluate the antimicrobial activity and potential use of plant extracts against four bacteria and two fungi. In general there were no statistically significant differences in MIC and total activity values and there were no clear trends across treatments. The applied water treatments did not cause significant effects on the antimicrobial activity of extracts. The fact that water stress did not materially influence antimicrobial activity does not mean that water stress does not affect other medicinal properties. Nevertheless our results question the general perception of traditional medicinal practitioners that plants growing under natural stress conditions have higher biological activities at least as far as water stress related to antimicrobial activities is concerned.

The effect of Beauveria bassiana inoculation on plant growth, volatile constituents, and tick (Rhipicephalus appendiculatus) repellency of acetone extracts of Tulbaghia violacea

“…T. violacea is frequently harvested from the wild by traditional healers, putting intense pressure on the wild populations [ 37 , 38 ]. Despite its medicinal uses, very few studies have focused on the optimization of the cultivation with the view of improving yield and quality of the medicinal materials, and bioactivity derived from this species [ 39 ].…”

A Proposal Towards a Rational Classification of the Antimicrobial Activity of Acetone Tree Leaf Extracts in a Search for New Antimicrobials

“…For bacteria, the inhibition was determined after 2 h and for fungi, after 24 h of incubation [23]. It is also clear that environmental conditions and also the season of growth can have an effect on the antimicrobial activity, although water stress and temperature stress did not have a major effect on the antimicrobial activity of some plants [29,30].…”

Constraints to Cultivation of Medicinal Plants by Smallholder Farmers in South Africa

“…Among some conservationists and social researchers, there is a reported concern about the acceptance of cultivated medicinal plants [58,81], as cultivated material is believed by some to lack spiritual power [82,83]. Although cultivated medicinal plant material is accepted as an alternative, certain South African conservative traditional health practitioners have expressed views suggesting that cultivated plants lack efficacy in healing.…”