Antimicrobial activity from Piper sarmentosum Roxb. against rice pathogenic bacteria and fungi

In vitro antimicrobial activity of the dichloromethane and methanol extracts of Piper sarmentosum leaves, fruits, stems, and the essential oil obtained from the fresh leaves together with their constituents were investigated against two rice pathogenic fungi: Rhizoctonia solani (sheath blight causal agent) and Bipolaris oryzae (brown spot causal agent), and two rice pathogenic bacteria: Xanthomonas oryzae pv. oryzae (Xoo) (bacterial leaf blight causal agent) and pv. oryzicola (Xoc) (bacterial leaf streak causal agent). Among them, the dichloromethane extracts of the leaves and fruits, and the essential oil showed significantly high potential anti-rice microbial activity. Based on bioassay-guided fractionation of the dichloromethane leave and fruit extracts, myristicin, sarmentine, brachystamide B, brachyamide B, and piperonal were isolated. Moreover, the major constituent of its oil was also myristicin. Myristicin and brachyamide B revealed the highest potent inhibition against R. solani and B. oryzae (half maximal inhibitory concentration (IC50) of 0.69 and 0.12 mmol L−1), respectively. Moreover, brachyamide B and piperonal displayed most antibacterial activity against Xoo (MIC/MBC 7.62/1.90 mmol L−1) and Xoc (MIC/MBC 2.59/20.75 mmol L−1), respectively. Additionally, the essential oil also exhibited the antimicrobial activity against all tested rice pathogenic bacteria and fungi. These compounds and the oil were first evaluated for anti-rice pathogenic microbial activity.