Agriculture & Food, Volume 8, 2020

Abstract: Cucumber is one of the most important agricultural products in many countries. Presently, the annual global cucumber production was approximately 71 million tonnes. Nonetheless, downy mildew, a common disease caused by Pseudoperonospora cubensis (PC), has led to a devastating impact on the quality of cucumber. The long-term usage of fungicide leads the occurrence of fungicide resistance and decreases host resistance. Emulsions synthized by oil could be an alternative for plant antifungal protectants. So far, no literature reported the effect of droplet size of emulsion on plant diseases. In this research, we synthesized environmental friendly antifungal micro/nano-emulsions using six types of oil (neem oil, moringa oil, soybean oil, cinnamon oil, clove oil, and camellia oil) and evaluated their antifungal activity of the emulsions upon the cucumber downy mildew. The key parameters affecting process of synthesizing droplet size of micro/nano-sized emulsions, including temperature, homogenization speed, oil to surfactant ratio, water ratio and surfactant ratio were evaluated. Then, the antifungal activity against cucumber downy mildew of these emulsions were tested via different oil types, oil concentrations (0.0125% - 0.1%), and droplet size of emulsions (100 - 1,000 nm). Results showed that 0.1% of moringa-type, cinnamon-type and clove-type emulsion had better antifungal efficacy compared to neem-type, soybean-type, and camellia-type. As decreasing the oil concentration from 0.1% to 0.025%, the disease incidence of moringa-type and cinnamon-type emulsion did not show significant changes, by contrast, the clove-type emulsion increased with decreasing oil concentration. The droplet size of cinnamon-type emulsion synthesized by 0.025% cinnamon oil increased from around 114 to 1,209 nm with the disease incidence increased from 6.67% to 30%, which could be attributed to collision of oil droplets and sporangia The findings suggest that cinnamon oil emulsion is an excellent antifungal agent and can be used for protecting cucumber from the incidence of downy mildew.