Discovery of Novel Compounds for Combating Rising Severity of Plant Diseases Caused by Fungi and Viruses

In recent years, the severity of plant diseases caused by plant pathogenic fungi and viruses has been on the rise. However, there is a limited availability of pesticide chemicals in the market for effectively controlling both fungal and viral infections. To solve this problem, a series of novel pyrimidine derivatives containing a 1,3,4-oxadiazole thioether fragment were synthesized. Among them, compound 6s exhibited remarkable in vivo protection activity against tobacco mosaic virus, demonstrating the superior 50% effective concentration (EC₅₀) value of 0.42 μM, outperforming ningnanmycin (0.60 μM). Meanwhile, compound 6s exhibited remarkable antifungal activity against Botrytis cinerea Pers. in postharvest blueberry in vitro, with an EC₅₀ value of 0.011 μM, surpassing the inhibition rate of Pyrimethanil (0.262 μM). Additionally, compound 6s also demonstrated remarkable curative and protection activities against blueberry fruit gray mold in vivo, with control efficiencies of 54.2 and 60.4% at 200 μg/mL concentration, respectively, which were comparable to those of Pyrimethanil (49.3 and 63.9%, respectively). Scanning electron microscopy showed that the compound 6s-treated hyphae of B. cinerea Pers. in postharvest blueberry became abnormally collapsed and shriveled. Furthermore, the molecular docking simulation demonstrated that compound 6s formed hydrogen bonds with SER-17, ARG-43, and SER-39 of succinate dehydrogenase (SDH), providing a possible explanation for the mechanism of action between the target compounds and SDH. This study represents the first report on the antiviral and antifungal activities of novel pyrimidine derivatives containing a 1,3,4-oxadiazole thioether fragment.