Effects and Inhibition Mechanism of Indole-3-Carboxaldehyde in Controlling Scutellaria baicalensis Root Rot

Scutellaria baicalensis Gorg is a medicinal herb of significant value in traditional Chinese medicine. Root rot is a major issue in S. baicalensis-producing areas. The aim of this study was to evaluate whether indole-3-carboxaldehyde, a metabolite derived from Purpureocillium lilacinum, has a significant effect on Fusarium solani (one of the main pathogenic fungi causing S. baicalensis root rot), and to clarify its antifungal mechanism. We evaluated the toxicity of indole-3-carboxaldehyde to F. solani using the growth rate assay and found that the EC50 value was 59.563 μg/mL; we also performed additional pot experiments under greenhouse conditions. The effects of indole-3-carboxaldehyde on fungal hyphal morphology and ultrastructure were evaluated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Indole-3-carboxaldehyde was found to induce the disintegration of the mitochondrial double membrane in F. solani, as well as cause cell wall separation. Further probing into the effects of indole-3-carboxaldehyde on mitochondrial aspects was conducted using enzyme activity test kits and real-time quantitative PCR. The findings indicated that indole-3-carboxaldehyde decreases the mitochondrial membrane potential; reduces the activities of SOD, CAT, POD, and GR enzymes; and hampers the growth of F. solani by suppressing the activity of mitochondrial electron transport chain complex I, resulting in H2O2 accumulation. This disruption of the mitochondrial antioxidant pathway impedes the effective clearance of reactive oxygen species (ROS), ultimately leading to the death of F. solani. Future studies of indole-3-carboxaldehyde should focus on its effect on metabolic pathways, which could facilitate the development of innovative pesticides.