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

Background The rice sheath blight caused by Rhizoctonia solani is a devastating disease for rice in China. However, unreasonable uses of chemical fungicides applied to control the disease raise major environmental and food safety issues. Ecofriendly biocontrol alternatives were urgently needed. Eugenol, one of the main ingredients in Syzygium aromaticum has drawn much attention owing to its antifungal properties. However, its mode of action on causing are still not clear. Herein, the antifungal activity and mode of action of eugenol against R. solani were investigated. Results The results confirmed that the mycelium of R. solani treated with eugenol were shrunk and dehydrated, the cytoplasmic wall separated, and the vacuoles and mitochondria decreased or dissolved. Moreover, we found that eugenol down-regulated the expression of C-4 methyl sterol oxidase, inhibited the synthesis of ergosterol, increased the membrane permeability and impaired the transportation of amino acids and glucose across the cell membrane. Additionally, eugenol also decreased the mitochondrial membrane potential and initiated an oxidative stress reaction by increasing reactive oxygen species and malondialdehyde, which together with membrane damage contributed to the antifungal activity of eugenol. Meanwhile, eugenol might inhibit R. solani via affecting oxidative phosphorylation and the TCA cycle. Conclusion In view of the multi-target properties of eugenol against R. solani, eugenol provides an alternative approach to chemical control strategies against rice sheath blight. This article is protected by copyright. All rights reserved.