Discovery of Highly Efficient Novel Potential Succinate Dehydrogenase Inhibitors Containing a Stilbene Group for Management of Sheath Blight of Rice and Sclerotinia Stem Rot of Oilseed Rape

In the search for novel succinate dehydrogenase inhibitors (SDHIs) fungicides for managing rice sheath blight (RSB) and sclerotinia stem rot (SSR), 28 pyrazole-4-carboxamides incorporating stilbene or diphenylacetylene scaffolds were synthesized and evaluated for antifungal activities. The results showed that compound 7m exhibited the most promising antifungal efficacy against Rhizoctonia solani and Sclerotinia sclerotiorum with EC50 (half maximal effective concentration) values of 0.004 and 0.028 μg/mL, outperforming Boscalid and Fluxapyroxad. Furthermore, the detached leaf assay showed that 7m showed remarkable protective and curative efficacies against R. solani and significant inhibition of S. sclerotiorum growth on oilseed rape leaves, indicating that it had a promising application prospect for RSB and SSR management. Further SDH enzymatic inhibition assay, scanning electron microscopy (SEM), molecular docking studies, and molecular dynamics (MD) simulations revealed that compound 7m shared an antifungal mechanism similar to that of Fluxapyroxad, which was further validated by density functional theory (DFT) and electrostatic potential (ESP) calculations. These findings suggested that 7m held significant promise as a novel SDHI for the effective management of RSB and SSR, warranting further investigation.