The main component of creosote obtained from dry wood distillation—guaiacol—is a natural antioxidant that has been widely used in pharmaceutical and food preservation applications. However, the antifungal mechanism of guaiacol against phytopathogens remains unclear. In this study, we found that guaiacol exerts inhibitory effects against mycelial growth, conidial formation and germination, and deoxynivalenol (DON) biosynthesis in Fusarium graminearum in a dose-dependent manner. The median effective concentration (EC50) value of guaiacol for the standard F. graminearum strain PH-1 was 1.838 mM. Guaiacol strongly inhibited conidial production and germination. The antifungal effects of guaiacol may be attributed to its capability to cause damage to the cell membrane by disrupting Ca2+ transport channels. In addition, the decreased malondialdehyde (MDA) levels and catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activity by guaiacol treatment indicate that guaiacol displays activity against DON production by modulating the oxidative response in F. graminearum. Taken together, this study revealed the potentials of antioxidant in inhibiting mycotoxins in F. graminearum.

Guaiacol (2-methoxyphenol), also called methylcatechol, is a white or yellow crystalline material or transparent yellow oily liquid that is mainly found in guaiac resin or pine oil in nature; in addition, guaiacol is the main component of creosote, which is obtained from dry wood distillation. Guaiacol is used in a wide range of industrial applications and often used to produce a variety of fragrances, such as eugenol, vanillin and artificial musk. Guaiacol is also widely used in medicine for the synthesis of guaiacol benzoate (potassium guaiacol sulfonate), as a local anesthetic or antiseptic, and in the preparation of oral solutions for expectoration and the treatment of indigestion. However, few studies on the use of guaiacol to inhibit plant pathogens have been reported. Some essential oils containing substituted phenols, such as eugenol, thymol, carvacrol and guaiacol, have strong antimicrobial and antioxidant activities. Vanilla extract and vanillin, which are rich in guaiacol, can inhibit the growth of Alternaria alternata. Some plant acids or wood vinegar solutions with antibacterial or antifungal effects are also rich in guaiacol. A recent study suggested that wheat straw vinegar can significantly inhibit the growth of F. graminearum and DON production, which the active ingredient is guaiacol compounds, but the antimicrobial activity of guaiacol against F. graminearum is poorly understood.

Therefore, in this work, we identified the inhibitory activity of guaiacol against the growth of F. graminearum and its production of DON. Guaiacol-induced disruption of the cell membrane in F. graminearum was studied by physiological assessment and microscopic observation. All of these results can improve our understanding of the action mode of guaiacol, which will assist us in providing new reference data for the management of FHB caused by F. graminearum.The standard strain of F. graminearum was PH-1 (NRRL31084), which is used to investigate the detailed physiological and biochemical responses under guaiacol treatment. The strains were grown on Potato Dextrose Agar (PDA) medium and Carboxymethyl Cellulose (CMC) medium for mycelial growth assay and sporulation assay, respectively. Trichothecene biosynthesis inducing (TBI) media was used for the DON production assay. Yeast extract peptone dextrose (YEPD) medium was used for conidial germination assays and fungal culture prior to quantitative real-time RT-PCR (qRT-PCR) analysis for gene expression. Guaiacol was stored at 4°C in darkness.