Effects and Inhibition Mechanism of Indole-3-Carboxaldehyde in Controlling <i>Scutellaria baicalensis</i> Root Rot

<i>Scutellaria baicalensis</i> Gorg is a medicinal herb of significant value in traditional Chinese medicine. Root rot is a major issue in <i>S. baicalensis</i>-producing areas. The aim of this study was to evaluate whether indole-3-carboxaldehyde, a metabolite derived from <i>Purpureocillium lilacinum</i>, has a significant effect on <i>Fusarium solani</i> (one of the main pathogenic fungi causing <i>S. baicalensis</i> root rot), and to clarify its antifungal mechanism. We evaluated the toxicity of indole-3-carboxaldehyde to <i>F. solani</i> 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 <i>F. solani</i>, 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 <i>F. solani</i> 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 <i>F. solani</i>. Future studies of indole-3-carboxaldehyde should focus on its effect on metabolic pathways, which could facilitate the development of innovative pesticides.