Guaiacol as a natural melanin biosynthesis inhibitor to control northern corn leaf blight

Abstract

BACKGROUND The natural 1,8‐dihydroxynaphthalene (DHN) melanin biosynthesis inhibitors (MBIs) are one of the promising approaches to the integrated management of plant diseases but have received scarce attention until now. Herein, to explore the natural DHN MBIs used in the control of northern corn leaf blight (NCLB), a library of 53 essential oil compounds was used to screen the MBIs against Exserohilum turcicum, the causal pathogen of NCLB, using tricyclazole as a reference compound. RESULTS The results of morphological change in the colony, thermogravimetric analysis, ultraviolet–visible spectroscopy, and transmission electron microscopy confirmed that guaiacol could effectively inhibit the melanin production at 50 μg/mL under in vitro conditions. The in vitro bioassay results indicated that this inhibition effect was concentration‐dependent and the minimum inhibition concentration of guaiacol was 50 μg/mL. The in vivo experimental results demonstrated that guaiacol significantly inhibited appressorium formation and penetration on corn leaf sheaths at the concentration of 500 μg/mL. The pot experiment results revealed that there were no differences between guaiacol (500 μg/mL) and tricyclazole (100 μg/mL) in control efficacy. The enzymatic assay suggested that guaiacol might exert the activity through inhibiting DHN polymerization to form melanins, which was distinct from tricyclazole. CONCLUSIONS Taken together, this study screened out guaiacol as a natural MBI from 53 essential oil compounds and verified its effectiveness in the control of NCLB at 500 μg/mL. Above all, this research opened an avenue for exploring natural DHN MBIs in the integrated management of plant diseases. © 2022 Society of Chemical Industry.

Dark Pigments in Entomopathogenic Fungal Microsclerotia: Preliminary Evidence of a 1,8-Dihydroxynaphthalene-melanin-like Compound in Metarhizium robertsii

“…This suggests that DHN-melanins might be present in the pigmented hyphal aggregates that the fungus differentiates in liquid culture, and that these dark pigments play an important role in MS formation and tolerance to both thermic and oxidative stress. Guaiacol, another inhibitor of DHN-melanin synthesis via a different mechanism to tricyclazole, possibly during melanin polymerization [26], also showed phenotypical and genic expression differences in the propagules obtained with its supplementation in the culture media. Thus, a hypothesis about the presence of DHN-melanin in this fungus is proposed.…”

“…There are two types of DHN-melanin synthesis inhibitors, which vary in their mechanism of action. While tricyclazole has inhibitory activity on the fungal reductases involved in the synthesis of 1,8-dihydroxynaphthalene, a key precursor of DHN-melanin, guaiacol blocks the polymerization reactions [26].…”