Activity-guided separation of Chromolaena odorata leaf extract reveals fractions with rice disease-reducing properties

An aqueous extract from the plant Chromolaena odorata [syn Eupatorium odoratum ], Eupatorieae, Asteraceae, protected rice against sheath blight by induced resistance. As an initial step towards identification of the specific disease-reducing compounds, leaves from C. odorata were extracted with water and methanol and the extracts separated using a group separation system followed by analysis using capillary electrophoresis. The fractions from the extracts were tested in vitro and in planta using Bipolaris oryzae (cause of brown spot of rice) to test for their potential to reduce disease severity. Activity-guided separation of the C. odorata extracts indicated that compounds with activity could, at least partly, be isolated on a weakly acidic cation exchange column. Further purification yielded fractions with disease reducing effects of up to 72 % at 15 days after inoculation. Activity was found both in methanol and water extracts, indicating that the bioactive compound(s) are hydrophilic, low molecular weight compounds. The disease-reducing fractions did not display any direct antimicrobial effects, but data indicate that they protect the plants by induced resistance as evidenced from increased activity of β-1,3-glucanase.