Eugenol induces apoptosis and autophagy of Rhizoctonia solani Kühn by destroying mitochondria structure and function

Rhizoctonia solani is a broadly destructive plant-pathogenic fungus with a wide host range. Eugenol has inhibitory activity against R. solani, making it a potential new antimicrobial agent. However, its mode of action at the cellular level has not been systematically elucidated.

Eugenol exhibited moderate fungicidal activity, and inhibited R. solani in a dose-dependent manner. Microscopically, the mycelial morphology showed signs of shrinkage and depression, along with an increase in vacuoles, uneven chromatin distribution, and mitochondrial deformation and dissolution. Transcriptome analysis showed that tricarboxylic acid cycle-related and programmed cell death-related genes exhibited significant changes in expression after eugenol treatment. Further biochemical experiments found that eugenol induced reactive oxygen species accumulation accompanied by an increase in malondialdehyde level (379% of control) and decrease in superoxide dismutase enzyme activity (57% of control) in mycelia. Eugenol treatment led to mitochondrial structural damage (collapse of the mitochondrial membrane potential and reduction in Tomm20 level) and functional disorders (decreases in Aconitase-2 level). In addition, characteristics typical of mycelial cell apoptosis were observed, including activation of the apoptosis executor caspase-3, decreased expression of the anti-apoptotic protein Bcl-2, and DNA fragmentation. Moreover, decreased expression of the autophagy marker protein p62 and the co-localization of intracellular lysosomes and mitochondria indicated that cells might clear damaged mitochondria through autophagy.

These findings collectively suggest that eugenol induces apoptosis and autophagy in R. solani mycelia mediated by mitochondrial damage, offering new insights into its antifungal mechanism at the cellular level. © 2026 Society of Chemical Industry.