Novel Pyrazole-4-carboxamide Derivatives with a Tetrahydroquinoline Skeleton: Promising SDHIs for the Control of Rhizoctonia solani.

In this study, 30 tetrahydroquinoline-based pyrazole-4-carboxamide derivatives were designed, synthesized, and screened for antifungal activities. Among them, compound 6m displayed the strongest inhibitory activity against Rhizoctonia solani, with a half-maximal effective concentration (EC50) as low as 0.03 μg/mL, superior to Boscalid (EC50 = 0.40 μg/mL) and Fluxapyroxad (EC50 = 0.06 μg/mL). Further detached-leaf assays on rice verified that 6m could markedly suppress the growth of R. solani with strong protective and curative effects even at 50 μg/mL. Follow-up mechanistic studies indicated that compound 6m might exert antifungal activity through SDH inhibition-related mechanisms. These findings suggested that compound 6m might be a potent candidate as a succinate dehydrogenase inhibitor (SDHI) against R. solani. Further research, including field trials and biosafety assessment, was needed to realize the potential of compound 6m as an effective tool for rice protection.