Antagonistic activity and defense mechanism of carvacrol and eugenol against Fusarium solani

Abstract:

[Background] Fusarium solani, one of the most destructive soil-borne pathogens worldwide, seriously affects the yield and quality of crops. Therefore, it is urgent to develop broad-spectrum sustainable biocontrol agents and the abundant secondary metabolites of plants are natural sources. [Objective] To explore the activity of carvacrol and eugenol against F. solani and the possible underlying mechanism. [Methods] With the mycelium growth rate method, crossing method, and spore germination method, the inhibitory effect of carvacrol and eugenol on mycelium growth and spore germination of F. solani was analyzed. The scanning electron microscope (SEM) was used for observing the mycelial morphology of F. solani, and propidium iodide (PI) staining was used for observing the damage to F. solani cell membrane. Moreover, the extracellular conductivity, protein content, and ergosterol biosynthesis were analyzed. [Results] Carvacrol and eugenol significantly suppressed the mycelial growth and spore germination of F. solani in a dose-dependent manner with the median effective concentration (EC₅₀) values of 92.39 μL/L and 263.00 μL/L, respectively. According to the observation under SEM, the cell wall and cell membrane of F. solani were damaged after exposed to carvacrol and eugenol. As a result, the mycelia had bends, folds, and depressions rather than the normal linear morphology. PI staining revealed that two essential oils broke F. solani cell membrane and enhanced the membrane permeability, resulting in the outflow of cytoplasmic contents and the surge in extracellular conductivity and protein content. After treatment with high concentration of carvacrol (400 μL/L) and eugenol (800 μL/L) for 48 h, the ergosterol content in F. solani decreased by 78.61% and 67.73%, respectively. [Conclusion] Carvacrol and eugenol inhibit the mycelial growth and spore germination of F. solani, damage the cell membrane, enhance membrane permeability, and disrupt the ergosterol biosynthesis on cell membrane, thereby exerting the antifungal activity. In conclusion, this study lays a theoretical basis for the screening of biocontrol agents of F. solani.