In vitro antifungal activity and mechanism of action of carvacrol against Sclerotinia sclerotiorum (Lib.) de Bary

This study aimed to examine the antifungal effects of nine monoterpenes on Sclerotinia sclerotiorum via the mycelial growth rate method. The effects of carvacrol on the morphological structures of hyphae were investigated by scanning electron microscopy (SEM). The oxalic acid (OA), total protein contents, and the activity of cell wall-degrading enzymes, including chitinase, cellulase and β-1,3-glucanase, were assessed. The results showed that the antifungal rates of carvacrol, thymol and eugenol reached 100% at a concentration of 400 mg/L, and the EC50 values of carvacrol, thymol, and eugenol were 43.40, 56.22, and 86.63 mg/L, respectively. The treatment of S. sclerotiorum with carvacrol had no significant effect on sclerotia formation, but the mycelial surface was shrivelled, uneven and broken, with cytoplasm flowing out. The OA content of S. sclerotiorum was significantly reduced to 133.78 µg/mL after treatment with carvacrol. Additionally, the total protein content of S. sclerotiorum mycelia in the carvacrol treatment group was significantly reduced to 15.67 µg/mL compared with that of the control group, and the activity of cellulase in the carvacrol treatment group was significantly higher than that in the control group.