Phytochemical composition and antibacterial activity of fruit extract of Solanum incanum L. against Ralstonia solanacearum

Abstract

Aims: To determine the phytochemical composition and antibacterial activity of Solanum incanum fruits against Ralstonia solanacearum. Study Design: Experimental design involving completely randomized design Place and Duration of Study: The study was conducted at department of Chemistry and Biochemistry, School of Sciences and Aerospace studies, Moi University, Kenya, between January and June 2021.Methodology: Extraction was done by maceration using ethanol as the extracting solvent. Phytochemical screening was done following standard procedures. Total Phenolic Content (TPC) and Total Flavonoid Content (TFC) were determined using the Folin–Ciocalteu colorimetric method and aluminum chloride colorimetric assay respectively. The extract was further analyzed using Gas Chromatography Mass spectroscopy (GC-MS) and Fourier transformed Infrared (FT-IR). In vitro antibacterial activity was determined using disc diffusion method while in vivo studies was done under greenhouse conditions. Results: Phytochemical analysis showed presence of alkaloids, glycosides, steroids, tannins, flavonoids, phenols, saponins and terpenoids. The TPC and TFC were found to be 84.997 ± 0.2 mg GAE/g and 20.535 ± 0.2 mg/g QE of dried sample respectively. GC-MS analysis revealed the presence of 15 compounds, (9E)-1-Methoxy-9-Octadecene (26.85%), 9-Octadecenamide (Z) (21.43%), E-15-Heptadecenal (7.28%), E-14-Hexadecenal (6.28%), 2,4-Di-tert-butylphenol (4.96%) among others. FT-IR analysis revealed presence of OH, C-H, N-H, CO functional groups at wavenumbers 3348 cm -1 , 2931 cm -1 , 1589 cm -1 , and 1218 cm -1 respectively. The antibacterial activity for in vitro studies at concentrations 0.01, 0.05, 0.10, and 0.15 g/10 mL, the diameters of zone of inhibition were 20.75 ± 1.3, 25.75 ± 0.5, 27.25 ± 0.5, and 30.75 ± 0.5 mm respectively. This was comparable (P= .02) to that of ampicillin (positive control) which had zones of inhibition of 26.75 ± 0.5, 28.75 ± 0.5, 31.75 ± 0.4, and 35.00 ± 0.0 mm at the concentrations respectively. For the in vivo studies the plant extract and ampicillin delayed the development of the disease by eight and ten days post-inoculation respectively while symptoms of bacterial wilt for water treatment (negative control) were observed four days post- inoculation. Conclusion: The plant extract had remarkable antibacterial activity and can be used to make viable formulations to control the devastating bacterial wilt disease.