Discovery of β-Carboline Oxadiazole Derivatives as Fungicidal Agents against Rice Sheath Blight

A series of beta-carboline oxadiazoles were synthesized, and their fungicidal activities and mechanism of action against rice sheath blight caused by Rhizoctonia solani was evaluated. The results showed that all of these compounds exhibited significant in vitro fungicidal activity. Significantly, compound Si (EC50 = 4.2 mu g/mL) displayed the best efficacy and superior fungicidal activity compared to validamycin A (EC50 = 197.6 mu g/mL). Moreover, the in vivo test also demonstrated that compound Si could effectively control rice sheath blight and showed higher in vivo protective and curative activities against R. solani than validamycin A. Preliminary mechanism studies revealed that compound Si caused the loss of mitochondrial membrane potential, reactive oxygen species accumulation, cell membrane destruction, and DNA synthesis interference. These findings indicated that compound Si displayed superior fungicidal activities against R solani and could be a potential fungicidal candidate against rice sheath blight.