Rosin-Based Schiff Derivatives as Potent Fungicidal Agents against Rhizoctonia Solani : Fungicidal Activity Evaluation and Mode of Action Insights

This study developed a series of rosin-based Schiff derivatives to control rice sheath blight caused by Rhizoctonia solani, with azoxystrobin as a positive control in in vitro fungicidal screening across eight phytopathogens. Compound 3c displayed the most potent inhibitory effect against R. solani (effective concentration value of 3.54 mg/L), outperforming azoxystrobin (8.64 mg/L). In vivo activity assays confirmed that 3c exerted significant protective and curative effects on rice plants, with values of 84.0% and 78.9%. Morphological and ultrastructural observations revealed that 3c destroyed cell structures and triggered a cytoplasmic leakage. Physiological and biochemical analyses indicated that 3c inhibited the activities of antioxidant enzymes (especially the catalase enzyme), disrupting intracellular redox homeostasis, detoxification capacity, and energy metabolism. Molecular docking results demonstrated that 3c stably bound to the active site of CAT through hydrogen bonds and hydrophobic interactions. Collectively, these findings suggest that 3c is a promising fungicidal candidate for sustainable management of rice disease.