Comparative study of roots of five Solanum species grown in Sri Lanka

Abstract

Genus Solanum is economically significant as both medicinal and nutritional crops. Solanum insanum L. (Elabatu), Solanum melongena L. (Wambatu), Solanum torvum Sw. (Thibbatu), Solanum violaceum Ortega (Thiththa thibbatu) and Solanum trilobatum L. (Wel thibbatu) grow well in Sri Lanka. Amongst them roots of S. violaceum Ortega, S. trilobatum L. and most commonly the roots of S. insanum L. are utilized as raw materials in Ayurveda. The objectives of this study were to identify root anatomical structures such as stone cells, vessels, starch grains, various types of crystals and fibers of these five Solanum species quantitatively and to examine the root chemical constituents in the form of fingerprint through the application of Thin Layer Chromatography (TLC). Fluorescence study was carried out to differentiate species with respect to nature of the chemicals present. Plants were collected from Gampaha district with maturity age between 12–15 months. One-way ANOVA was used in the quantitative anatomical data analysis. For root anatomical studies; free hand sections were taken using sharp blades and the sections were mounted using chloral hydrate and glycerine. All five Solanum species had similar root anatomical structures with a few differences. Parenchyma cells were in the cortex next to the outermost few layers of brownish cork cells. Inner to the cortex was the phloem. Solitary and grouped vessels were present in the centre, surrounded by tracheids and fibers. Xylem vessels and tracheids were simple pitted. Parenchyma cells in the cortex were filled with simple and compound starch grains. Stone cells were present in the cortex. Calcium oxalate microcrystals were present in the cortex as black powdery substance. Medullary rays were uniseriate or multiseriate. Vessel width of S. torvum Sw. was significantly higher than the other four species at 0.05 significant level. S. trilobatum L. had a comparatively small stone cell width at 0.05 significant level. When the retention factor values of spots of Methanol extract were studied in TLC, only the roots of S. violaceum Ortega could be identified separately from the other four Solanum species. Fluorescence analysis under visible and UV light, filtrates of root powder samples with 50% H2SO4, 50% glacial acetic acid, 1N aqueous NaOH, 1 N alcoholic NaOH, chloroform, distilled water and ethyl acetate gave different colours. Filtrates of root powder samples of S. insanum L., S violaceum Ortega and S.trilobatum L. showed blue fluorescence with 50% H2SO4 while S. insanum L., S. torvum Sw. and S. violaceum Ortega showed blue fluorescence with 1 N aqueous NaOH under 366 nm UV light. Quantitative chemical analysis of root is recommended for further studies in order to differentiate roots of all these five Solanum species separately.