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 (EC 50 ) as low as 0.03 μg/mL, superior to Boscalid (EC 50 = 0.40 μg/mL) and Fluxapyroxad (EC 50 = 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.