Discovery of Potential Rosin-Based Triazole Antifungal Candidates to Control Valsa mali for Sustainable Crop Protection

To investigate the potential application value of dehydroabietic acid, 27 novel dehydroabietyl-1,2,4-triazole-5-thioether-based derivatives were designed and characterized by IR, 1H NMR, 13C NMR, and LC-MS. Their antifungal activities were evaluated against five plant fungi, namely, Valsa mali, Colletotrichum orbiculare, Fusarium graminearum, Sclerotinia sclerotiorum, and Gaeumannomyces graminis; the results showed that compound 5h-1 (Co. 5h-1) exhibited a considerable inhibitory effect against V. mali. Moreover, in vivo experiments indicated that Co. 5h-1 had a certain protective effect on apple branches. The preliminary structure–activity relationship analysis suggested that the electron-withdrawing group on the benzyl group was significantly better than that of other substituent derivatives. Through electron microscopy analysis, it was found that Co. 5h-1 hindered the growth of mycelia, damaged their cell structure, and caused the large accumulation of reactive oxygen species (ROS). Preliminary research on the mode of action indicated that Co. 5h-1 could affect the activity of CAT by increasing the α-helix (0.790%), decreasing the β-sheet (0.170%), which led to the accumulation of ROS. In addition, Co. 5h-1 also affected the activity of CYP51, hindered the biosynthesis of ergosterol, and increased cell membrane permeability. Overall, this above research proposed that Co. 5h-1 can be a novel leading structure for development of a fungicide agent.