Antifungal activity and mechanism of thymol against Fusarium oxysporum, a pathogen of potato dry rot, and its potential application

Dry rot is a major disease of potato during storage, which is caused by several Fusarium species. Biological control based on natural bioactive compounds that inhibit tuber disease provides an attractive alternative because they are ecofriendly and low toxic. In this study, a monoterpene phenol thymol (2-isopropyl-5-methylphenol) was found to have an effective antifungal effect against Fusarium oxysporum, the pathogen of potato dry rot in vitro and in vivo. After thymol treatment, the inhibition of mycelial growth was dose-dependent with thymol concentration, and the mycelial bending was obvious. The IC50 was 26.4 mg/L, and 80 mg/L thymol almost completely inhibited the growth of F. oxysporum. At 20 and 60 mg/L thymol, the spore germination rate of F. oxysporum decreased by 40 % and 80 % respectively compared with the control group. The pathogenicity and spore viability of F. oxysporum was significantly reduced after the treatment of thymol, while thymol did not alter chitin deposition. In addition, thymol could also improve the sensitivity of F. oxysporum to environment stresses (high/low temperature, UV, etc.) and induce the potato pieces to resist F. oxysporum. Furthermore, thymol had synergistic and additive effect on F. oxysporum with chemical fungicides mancozeb and carbendazim, respectively. A total of 370 differentially expressed genes (DEGs) were obtained from F. oxysporum treated with or without thymol. The analysis of Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway showed that DEGs were mainly related to metabolism, transport, membranes, etc. In general, this study provides a new idea for the development of thymol as an eco-friendly agent for the control of potato dry rot.