Discovering the antibacterial activity of tryptanthrin derivatives for controlling kiwifruit canker and tobacco wilt disease.

Background: Plant bacterial diseases have severely affected the yield and quality of agricultural products, among which kiwifruit canker and bacterial wilt disease, caused by Pseudomonas syringae pv. actinidiae (Psa) and Ralstonia solanacearum (Rs), respectively, seriously restrict the development of the related industry. However, there are few effective green agents available to target these diseases.

Results: Herein, we synthesized 41 novel derivatives of the natural product tryptanthrin, among which partial compounds showed noticeable antibacterial activity against Psa and Rs. Compounds T7NO-4 and T7NH-2 can affect bacterial biofilm formation, change the membrane permeability, and cause bacterial necrosis. Compound T7NO-4 exhibits effective control activity against kiwifruit canker disease, with protective and curative efficiency of 75.61% and 66.84%, respectively. Compound T7NH-2 exhibits good protective activity against tobacco wilt disease but poor curative activity. To improve its curative activity, considering the characteristic that bacterial wilt disease is more prone to outbreak under weakly acidic soil conditions, introducing a ZIF-8 framework to make T7NH-2@ZIF-8 nanoparticles that exhibit pH-responsive release, then making T7NH-2@ZIF-8@TA through modifying with tannic acid (TA). T7NH-2@ZIF-8@TA nanoparticles exhibit superior efficacy against tobacco wilt disease.

Conclusion: This study demonstrates that 7-piperazine tryptanthrin derivatives exhibit good inhibitory activity against Psa and Rs and may be promising lead agents against plant bacterial diseases, with improved biological activity through being loaded into nanocarriers. © 2025 Society of Chemical Industry.