Antimicrobial Potential of a Quinoline‐Based Novel Schiff Base Against Tomato Crop Pathogens

Abstract This study introduces a novel Schiff base ligand ( L ) and its metal complexes (L‐Cu 2+ , L‐Ni 2+ , and L‐Zn 2+ ), which exhibit remarkable antifungal and antibacterial activity against the plant pathogens Alternaria solani and Xanthomonas euvesicatoria , the causative agents of early blight and bacterial spot in tomatoes, respectively. At 250 µg/mL, all compounds demonstrated exceptional antimicrobial activity, achieving 100% inhibition of A. solani , surpassing the commercial fungicide's 91% inhibition. Additionally, the compounds produced substantial inhibition zones against X. euvesicatoria . They also showed scavenging of reactive oxygen species (ROS), indicating their potential to mitigate oxidative stress in plant cells. Phytotoxicity tests at 300 µg/mL confirmed that none of the compounds adversely affected tomato seed germination. The dual action of pathogen inhibition and ROS neutralization, combined with non‐toxicity to plants, suggests that L and its complexes are promising candidates for crop protection. Across all assays, efficacy was ranked as L‐Cu 2+ > L > L‐Zn 2+ ≈ L‐Ni 2+ , with the L‐Cu 2+ complex demonstrating superior overall performance.