Unraveling the polypharmacology of a natural antifungal product, eugenol, against Rhizoctonia solani

BACKGROUND Rice sheath blight caused by Rhizoctonia solani is a devastating disease of rice in China. However, indiscriminate use of chemical fungicides applied to control the disease raise major environmental and food safety issues. Ecofriendly biocontrol alternatives are urgently needed. Eugenol, one of the main ingredients in Syzygium aromaticum, has attracted much attention owing to its antifungal properties. However, its mode of action is still not clear. Herein, the antifungal activity and mode of action of eugenol against R. solani were investigated. RESULTS Results confirmed that the mycelia of R. solani treated with eugenol shrank and became dehydrated, the cytoplasmic wall separated, and the vacuoles and mitochondria decreased or dissolved. Moreover, we found that eugenol downregulated expression of C-4 methyl sterol oxidase, inhibited synthesis of ergosterol, increased membrane permeability and impaired the transportation of amino acids and glucose across the cell membrane. In addition, eugenol decreased the mitochondrial membrane potential and initiated an oxidative stress reaction by increasing reactive oxygen species and malondialdehyde, which together with membrane damage contribute to the antifungal activity of eugenol. Meanwhile, eugenol might inhibit R. solani by affecting oxidative phosphorylation and the tricarboxylic acid cycle (TCA cycle). CONCLUSION In view of its multitarget properties against R. solani, eugenol provides an alternative approach to chemical control strategies against rice sheath blight.

Automated summary

Eugenol, a main component of Syzygium aromaticum, exhibits antifungal properties by causing morphological changes in Rhizoctonia solani mycelia, downregulating expression of C-4 methyl sterol oxidase, inhibiting ergosterol synthesis, increasing membrane permeability, impairing transportation of amino acids and glucose, as well as affecting oxidative phosphorylation and the tricarboxylic acid cycle. Additionally, eugenol induces oxidative stress by decreasing mitochondrial membrane potential, increasing reactive oxygen species, and malondialdehyde levels, ultimately contributing to its antifungal activity against R. solani.