|GILL, TORRENCE - US Department Of Agriculture (USDA)|
|LI, JIANMING - Purdue University|
|DOPPLER, MEGAN - Purdue University|
|Scofield, Steven - Steve|
Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2016
Publication Date: 10/1/2016
Citation: Gill, T.A., Li, J., Doppler, M., Scofield, S.R. 2016. Thymol-based sub-micron emulsions exhibit antifungal activity against Fusarium graminearum and inhibit Fusarium head blight (FHB) in wheat. Journal of Applied Microbiology. 4:1103-1116. doi:10.1111/jam.13195.
Interpretive Summary: Fusarium graminearum is the fungus that causes the devastating disease of wheat and barley, Fusarium head blight (FHB). This disease not only greatly lowers grain yield and quality, but also causes the grain to become contaminated with the dangerous mycotoxin, deoxynivalenol (DON). This paper explores the ability of the naturally occurring compound, thymol, to act as a fungicide and provide control of FHB. Thymol is purified from essential oils of plants and has very low solubility. To overcome this solubility problem and achieve uniform spray application, thymol micro-emulsions, with and without oil, were tested. Significant reduction in FHB development was observed when 0.1% thymol micro-emulsions were tested. These findings highlight the potential for control of an important disease of wheat and barley using plant-derived, and therefore more environmentally acceptable compounds.
Technical Abstract: Fusarium graminearum is a very destructive fungal pathogen that leads to Fusarium head blight (FHB) in wheat, a disease that costs growers millions of dollars annually both in crop losses and control measures. Current countermeasures include the deployment of wheat varieties with some resistance to FHB in conjunction with timed fungicide treatments. In this paper we introduce a fungicide based on thymol, a naturally occurring plant phenolic derived from essential oils. To overcome the hydrophobicity of thymol, the thymol active was incorporated into a unique sub-micron emulsion platform with and without a carrier oil to facilitate aqueous delivery. The minimum inhibitory concentration (MIC) was found to be 0.005% for thymol alone, and 0.01% with the inclusion of an oil component. Time kill experiments showed that thymol emulsions were able to inactivate Fusarium graminearum in as little as 10 seconds at concentrations above 0.06%. Spraying the thymol emulsions (~0.1% range) on the Bob White strain of wheat demonstrated drastic reductions in FHB infection rate (number of infected spikelets). However, with 0.5% thymol, the wheat heads exhibited premature senescence. Transmission and scanning electron micrographs suggests that the mechanism of antifungal action is membrane mediated, as conidia exposed to thymol showed complete organelle disorganization and evidence of lipid emulsification. The collective experimental data suggest thymol emulsions may be a natural alternative to traditional chemical fungicides in ameliorating FHB.