Gill T A, Li J, Saenger M, Scofield S R
Department of Agronomy, College of Agriculture, USDA-ARS Purdue University, West Lafayette, IN, USA.
Department of Basic Medical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN, USA.
J Appl Microbiol. 2016 Oct;121(4):1103-16. doi: 10.1111/jam.13195. Epub 2016 Aug 9.
Fusarium graminearum is a very destructive fungal pathogen that leads to Fusarium head blight (FHB) in wheat, a disease which costs growers millions of dollars annually both in crop losses and in remediation efforts. Current countermeasures include the deployment of wheat varieties with some resistance to FHB in conjunction with timed fungicide treatments. In this article, 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 low-surfactant submicron emulsion with and without a carrier oil.
The minimum fungicidal concentration of F. graminearum was found to be both 0·02% for thymol emulsions with and without an oil component. Time-to-kill experiments showed that thymol emulsions were able to inactivate F. graminearum in as little as 10 s at concentrations above 0·06%. Spraying the thymol emulsions (~0·1% range) on the wheat variety Bobwhite demonstrated significant 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 suggest 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 that thymol emulsions may be an effective naturally derived alternative to the current thymol treatments, and chemical fungicides in ameliorating FHB.
This is the first thymol-derived nanoemulsion particles resuspended into water and not DMSO, exhibiting the same antibacterial/antifungal activity as previously described thymol and thyme oil treatments. This drastically reduces the environmental footprint thymol will leave if utilized as a fungicide treatment on field crops.
禾谷镰刀菌是一种极具破坏性的真菌病原体，可导致小麦赤霉病，这种疾病每年给种植者造成数百万美元的作物损失和补救成本。目前的应对措施包括部署对赤霉病有一定抗性的小麦品种，并结合适时的杀菌剂处理。在本文中，我们介绍一种基于百里香酚的杀菌剂，百里香酚是一种从精油中提取的天然植物酚类物质。为了克服百里香酚的疏水性，将百里香酚活性成分加入到有或没有载体油的低表面活性剂亚微米乳液中。
发现对于有或没有油成分的百里香酚乳液，禾谷镰刀菌的最低杀菌浓度均为0.02%。杀菌时间实验表明，在浓度高于0.06%时，百里香酚乳液能够在短短10秒内使禾谷镰刀菌失活。在小麦品种“博白”上喷洒百里香酚乳液（约0.1%范围）显示赤霉病感染率（感染小穗数）显著降低。然而，使用0.5%的百里香酚时，小麦穗出现过早衰老。透射和扫描电子显微镜照片表明，抗真菌作用机制是膜介导的，因为暴露于百里香酚的分生孢子显示细胞器完全紊乱以及脂质乳化的迹象。
综合实验数据表明，百里香酚乳液可能是当前百里香酚处理方法以及化学杀菌剂在改善赤霉病方面的一种有效的天然替代物。
这是首次将百里香酚衍生的纳米乳液颗粒重新悬浮于水中而非二甲基亚砜中，其表现出与先前描述的百里香酚和百里香油处理相同的抗菌/抗真菌活性。这极大地减少了如果将百里香酚用作大田作物杀菌剂处理时其对环境的影响。
