Phytochemical Composition, Preparation And Characterization Of Biochar Composite From Solanum Incanum Fruits For Control Of Bacterial Wilt In Tomato Plants

Abstract

Ralstonia solanacearum causes bacterial wilt in tomato plants thereby leading to severe losses of the crop. This has led to the overuse of chemical pesticides often resulting to environmental contamination and human health risks as well as development of resistant strains of bacteria to several chemical pesticides. Therefore, there is need for novel methods to control bacterial wilt. This study focuses on the use of biochar composites and Solanum incanum fruit extracts to control bacterial wilt in tomato plants. The specific objectives were to: determine the phytochemical composition of the extract; isolate and test the biochemical characteristics of R. solanacearum; characterize biochar prepared from S. incanum fruits biomass; and compare the effectiveness of the plant extract, biochar composite, and ampicillin in control of R. solanacearum. Maceration method using ethanol as the solvent was used in extraction. Phytochemical screening was done following standard methods. The extract was analyzed using Gas Chromatography-Mass Spectroscopy (GC-MS) and Fourier Transformed Infrared (FT-IR). Ralstonia solanacearum was isolated by plating the bacterial tuber exudate on Triphenyl Tetrazolium Chloride (TZC). The residual biomass was transformed into biochar at pyrolysis furnace temperatures of 300 ℃ and 500 ℃ and characterized using FT-IR and scanning electron microscope (SEM). In vitro and in vivo studies were done to determine the antibacterial activity of the plant extract, biochar composite, and ampicillin. Phytochemical screening showed the presence of alkaloids, flavonoids, phenols, saponins, tannins and terpenoids. FT-IR spectra showed peaks at 3415 cm-1, 2931 cm-1, 1596 cm-1, and 1398 cm-1 for O-H, C-H, C=C, and C-O-H groups respectively. GC-MS results of the extract showed 15 compounds, with (9E)-1-Methoxy-9- octadecene (26.85%) as the major compound and others like 2-4-Di-tert-butylphenol, n- Tetracosanol-1, 1-Tridecene, E-15-Heptadecenal. The SEM images showed differences in morphological properties with the biochar prepared at 500 ℃ being more porous than that for 300 ℃. The in vitro antibacterial activity of the plant extract showed an inhibition zone of 30.75 ± 0.5 mm at a concentration of 0.15g/10 mL compared to ampicillin with a zone of inhibition of 35.00 ± 0.0 mm at the aforementioned concentration (P< 0.05). In the in vivo studies, distilled water treatment had a disease incidence of 100% 10 days post- inoculation (dpi). Plant extract and ampicillin treatment had a disease incidence of 100% and 60.0% respectively, 16 dpi. Activated biochars for 300 ℃ and 500 ℃ had a disease incidence of 80.0% and 66.7% respectively, 30 dpi. Biochar composite for 300 ℃ had a disease incidence of 73.3%, 64.5%, 60.0%, 22.2%, 13.3%, and 0% at a concentration of 1%, 2%, 3%, 4%, 5%, and 7% respectively, 30 dpi. Biochar composite for 500 ℃ showed disease incidences of 60.0%, 46.7%, and 22.2% at 1%, 2%, and 3% concentrations respectively, 30 dpi. No symptoms were observed at a concentration of 4%, 5%, and 7%. In conclusion, biochar composite is more effective in managing bacterial wilt than activated biochar, ampicillin, and plant extract. Biochar composite for 500 ℃ is recommended as a substitute for synthetic pesticides.