Novel Carbazole-Triazole-Thioether Conjugates as Multifunctional Antimicrobial Agents against Phytopathogen

Carbazole and triazole derivatives exhibit diverse biological activities and pharmacological properties. Herein, we report a series of novel 1,2,4-triazole thioethers containing carbazole moiety and evaluate their biological activities. The results showed that some titles exhibit excellent antibacterial activities against Xanthomonas axonopodis pv. citri ( Xac ) in vitro . In particular, E36 exhibits the most excellent antibacterial effect against Xac , with EC ₅₀ values of 9.4 mg/L, which was significantly better than the control drugs Bismerthiazol (BMT, EC ₅₀ values of 70.5 mg/L) and Thiodiazole-copper (TDC, EC ₅₀ values of 96.0 mg/L). Meanwhile, E36 exhibits a significant in vivo effect against Xac , with the therapeutic and protective efficacy of 48.57% and 51.96%, respectively, at a concentration of 200 mg/L, which was superior to TDC and equivalent to BMT. Additionally, E36 also exhibits exciting antifungal activity against Verticillium dahliae . Our study further demonstrates that compound E36 attenuates the pathogenicity of Xac by suppressing bacterial motility and extracellular polysaccharide (EPS) production, while it enhances host disease resistance by upregulating the expression of the citrus rbcL protein, thereby promoting carbon fixation and improving photosynthetic efficiency. This work indicates that 1,2,4-triazole thioethers containing carbazole moiety has the potential to be developed as a novel germicide.