Diphenyl Ether Hydrazone Derivatives as Novel Succinate Dehydrogenase Inhibitors for Effective Control of Rice Sheath Blight

Rice sheath blight, caused by Rhizoctonia solani pathogen, poses a significant threat to global food security. To address this challenge, we designed and synthesized diphenyl ether hydrazone derivatives (3aa-3bb) as potential succinate dehydrogenase inhibitors. Most of these derivatives achieved 100% inhibition against R. solani at 50 μg/mL concentration. Notably, compound 3az exhibited an exceptional efficacy of 95% control rate with an EC₅₀ of 0.28 μg/mL, which significantly outperformed boscalid at a concentration of 200 μg/mL, without affecting the rice growth and development. Furthermore, after treatment with 3az, the growth morphology and intracellular changes of R. solani mycelia were consistent with those observed with boscalid. Additionally, the IC₅₀ values of compounds 3ay and 3az were 1.55 and 1.11 μM, respectively, which were better than the IC₅₀ value of boscalid (1.85 μM). The finding by molecular docking studies revealed that compound 3az interacts with novel binding sites, offering an opportunity for the development of innovative SDH inhibitors for the efficient control of rice sheath blight disease.