A potential antifungal agent: Insight into the antifungal mechanism against Phomopsis sp

19 myricetin derivatives containing thiazole were designed and synthesized. Their fungicidal activities in vitro against ten species of plant pathogenic fungi were evaluated. Bioassay results indicated that some of compounds exhibited remarkable antifungal activities. Among them, Z17 showed the strongest antifungal activity against Phomopsis sp, with in vitro EC50 of 12.3 µg/mL, which was superior to those of the control drug azoxystrobin (32.2 µg/mL) and fluopyram (77.7 µg/mL). In addition, Z18 also had the inhibitory activity against the Alternaria brassicae, with an EC50 value of 32.5 µg/mL, which was much higher than azoxystrobin (49.3 µg/mL). Z17 exhibited good protective activity (62.5%) against Phomopsis sp on kiwifruit in vivo at 200 µg/mL. The results of in vivo experiments revealed that Z18 could effectively defend against the infestation of cabbage by Alternaria brassicae, and improve the protection ability of the crop. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) demonstrated that Z17 could destroy the integrity of cell membrane of pathogen Phomopsis sp, thus affecting the normal growth of mycelia. The results of the mechanism research further confirmed that the action of Z17 changed the mycelial morphology of Phomopsis sp, affected the permeability of cells, increased the leakage of cytoplasm and MDA contents. Molecular docking simulation results revealed that compound Z17 could readily bind with the active site of SDH and could be a potential SDH inhibitor. In summary, this study provides new ideas for effectively controlling plant fungal diseases and developing new green chemical pesticide products.