Potent Bacteriostatic Activity of a Naphthalene-2-Acyl Imidazolium Salt against Xanthomonas oryzae pv. oryzae

Rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) remains a serious yield threat. To identify selective antibacterials, we synthesized a small library of naphthalene-2-acyl imidazolium salts (NAIMSs) and evaluated their anti-Xoo activity. Diskdiffusion assays of 18 analogues revealed a clear structure-activity relationship: isopentyloxy-substituted derivatives were active, whereas others were not. Among them, NAIMS1f exhibited potent inhibition with a minimum inhibitory concentration of 0.75 μg mL-1. Growth kinetics demonstrated bacteriostatic action, completely suppressing low-inoculum growth but not killing high-density cultures. NAIMS1f showed higher sensitivity toward Xoo than Escherichia coli, Bacillus pumilus, or Pseudomonas syringae, defining a useful sensitivity window. These findings identify NAIMS1f as a promising lead for Xoo-focused inhibition in vitro and provide a basis for future mechanistic and pre-field validation studies.