ANTIBACTERIAL ACTIVITY OF HYDROALCOHOLIC EXTRACTS FROM Ricinus communis L. AND Tagetes erecta L. AGAINST PHYTOPATHOGENIC BACTERIA OF AGRICULTURAL IMPORTANCE

Abstract

Phytopathogenic bacteria are responsible for many crop diseases, and their control is largely based on chemical products that can generate resistance and tolerance. Plant extracts represent an alternative and a potential source of compounds with antibacterial activity. In this study, the antibacterial activity of hydroalcoholic extracts of Ricinus communis L. leaves and Tagetes erecta L. flowers was determined against the phytopathogenic Gram-positive bacterium (GPB) Clavibacter michiganensis subsp. michiganensis and the Gram-negative bacteria (GNB) Pseudomonas syringae pv. tomato and Xanthomonas campestris. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values are reported. The extracts were obtained by maceration, and their phytochemical constituents were determined through chemical screening, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Both extracts showed bactericidal activity against the three bacteria. While P. syringae and X. campestris were more sensitive to the extract of R. communis leaves, C. michiganensis was more sensitive to the extract of T. erecta flowers. The most sensitive bacterium was X. campestris, showing the lowest MIC and MBC values for the extract of R. communis leaves (0.195 and 0.39 mg mL-1, respectively). The bactericidal activity of R. communis leaves against the GNB could be associated with their higher TPC and TFC values compared with those of T. erecta flowers. However, a lower MBC was obtained with the T. erecta flower extract against C. michiganensis. This shows the importance of the chemical structure of secondary metabolites, which is related to their mode of action. In addition, the extract of T. erecta flowers showed a narrower MBC range (25–100 mg mL-1) against the three bacteria than the extract of R. communis leaves (0.39–200 mg mL-1). Therefore, the hydroalcoholic extract of T. erecta flowers could be a valuable source of secondary metabolites for controlling these phytopathogenic bacteria.