Effect of Vermicompost Leachate on Biomass and Antibacterial Properties of Five Bulbous Medicinal Plants: A Case Study From KwaZulu Natal, South Africa

Abstract

Study was done on biomass and antibacterial activity of five bulbous medicinal plants using vermicompost leachate (VCL), from KwaZulu Natal, South Africa. Vermicompost Leachate is a liquid generated by earthworms and microorganisms during the conversion of the organic matter into Vermicompost. One year- old seeds of (Bulbine natalensis, Merwilla plumbea, Tulbaghia violacea, Drimia robusta, and Bowiea volubilis) were subjected to VCL at different concentrations. Three concentrations of VCL, prepared by diluting with water in ratios of 1:5, 1:10 and 1:20 v/v on growth and biomass in green house were applied and harvested after 120 days. Bulbine natalensis seedlings treated with VCL at 1:10 concentration showed a significantly higher result compared to other treatments. Merwilla plumbea treated at higher concentrations of VCL (1:10 and 1:120) showed significantly high growth rate compared to the control. Tulbaghia violacea treated with VCL concentration of 1:20 showed significance compared to the control. However, seedling treated with VCL concentration of 1:20, all other treatments showed significance compared to control. Drimia robusta and Bowiea volubilis treated with different concentration of VCL showed significant increase in shoot length, number of leaves; shoot fresh weight and leaf area as compared to the control. From this study it was concluded that, vermicompost leachate has potential alternatives for improving the growth biomass of medicinal plants in terms of cost and environmental implications. Antibacterial activities were also evaluated using the micro-dilution assay against two Gram-positive (Bacillus subtilis, Staphylococcus aureus) and one Gram-negative bacteria (Escherichia coli). High activity was observed in the EtOH extracts in all the plants. Water extracts of B. natalensis exhibited higher activity against all the three bacterial strains. The dichloromethane (DCM) extracts of B. natalensis showed the lowest activity with a minimum inhibitory concentration (MIC) value of 0.098 mg/ml against S. aureus in VCL dilutions of 1:10 and 1:20 and 0.39 mg/ml against E. coli in all dilutions. Merwilla plumbea rhizome exhibited low activity with a MIC value of 0.78 mg/ml against E. coli compared to the Gram-positive bacterial strains. VCL dilutions of 1:10 and 1:20 could successfully be used to enhance the antibacterial properties of these bulbs.