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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #321021

Title: Characterization and Application of a Nanoemulsion for Controlling Citrus Huanglongbing

item YANG, CHUANYU - University Of Florida
item POWELL, CHARLES - University Of Florida
item Duan, Ping
item Shatters, Robert - Bob
item ZHANG, MUQING - University Of Florida

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2016
Publication Date: 9/30/2016
Citation: Yang, C., Powell, C.A., Duan, Y., Shatters, R.G., Zhang, M. 2016. Characterization and Application of a Nanoemulsion for Controlling Citrus Huanglongbing. Plant Disease. 100(12):2448-2454.

Interpretive Summary: Ca. Liberibacter asiaticus a bacterial pathogen that causes Huanglongbing (HLB), also called citrus greening disease, lives in the phloem of citrus trees. To kill this bacteria, compounds need to penetrate the bark or citrus leaf surface which acts as a strong barrier preventing the entry of many chemical compounds into the tree. To overcome this barrier and increasing the efficacy of chemical control, we developed a nanoemulsion method that makes the chemical small enough to pass through the surface of the tree and target the bacteria living in the phloem. In addition, we used this newly developed method to deliver five compounds into a diseased tree. The nanoemulsion method increased the antibacterial effect of these compounds. The novel formulations we developed shows more efficient elimination of Ca. Liberibacter asiaticus in HLB-affected citrus plants.

Technical Abstract: Nanoemulsion is a promising delivery system that increases utilization efficiency of pesticides and enhances the therapeutic efficiency against pathogens. The pathogen Candidatus Liberibacter asiaticus (Las), which can cause destructive citrus disease huanglongbing (HLB), resides in citrus phloem. Based on various physiochemical characteristics of oils, surfactants, and organic solvents, a novel oil-in-water (O/W) nanoemulsion was optimized to combat citrus HLB disease. The nanoemulsion was produced using a spontaneous emulsification method for the efficient delivery of ampicillin into citrus phloem by applying it to bark. The nanoemulsion prepared from cremophor® EL (viscous oil), acetone (water miscibility organic solvent), and Span 80/Tween 80 (surfactant) exhibited a small droplet size (13.68 ± 0.26 nm). It also had an improved absorption rate, including a 2 d peak concentration (tmax), 71.9 ng/g maximum concentration (Cmax), and 274.63 % relative bioavailability (RBA) of ampicillin in HLB-affected citrus compared to the Amp solution alone (tmax = 6 d, Cmax = 56.4 ng/g and RBA = 100 %). The same nanoemulsion was used to deliver five antimicrobials to control citrus HLB through the bark. We found that the nanoemulsion enhanced the therapeutic efficiency of validoxylamien A (increased by 57.58 %), combination of actidone and validoxylamine A (increased by 18.06 %), and sulfadimoethoxine sodium (increased by 22.22 %) against Las bacterium. Therefore, this study provides an efficient self-nanoemulsifying delivery system for controlling citrus HLB.