title: Antimicrobial Nanoemulsion Formulation with Improved Penetration of Foliar Spray through Citrus Leaf Cuticles to Control Citrus Huanglongbing.
abstract: Huanglongbing (HLB) is the most serious disease affecting the citrus industry worldwide to date. The causal agent, Candidatus Liberibacter asiaticus (Las), resides in citrus phloem, which makes it difficult to effectively treat with chemical compounds. In this study, a transcuticular nanoemulsion formulation was developed to enhance the permeation of an effective antimicrobial compound (ampicillin; Amp) against HLB disease through the citrus cuticle into the phloem via a foliar spray. The results demonstrated that efficiency of cuticle isolation using an enzymatic method (pectinase and cellulase) was dependent on the citrus cultivar and Las-infection, and it was more difficult to isolate cuticles from valencia orange (Citrus sinensis) and HLB-symptomatic leaves. Of eight adjuvants tested, Brij 35 provided the greatest increase in permeability of the HLB-affected cuticle with a 3.33-fold enhancement of cuticular permeability over water control. An in vitro assay using Bacillus subtilis showed that nanoemulsion formulations containing Amp (droplets size = 5.26 ± 0.04 nm and 94 ± 1.48 nm) coupled with Brij 35 resulted in greater inhibitory zone diameters (5.75 mm and 6.66 mm) compared to those of Brij 35 (4.34 mm) and Amp solution (2.83 mm) alone. Furthermore, the nanoemulsion formulations eliminated Las bacteria in HLB-affected citrus in planta more efficiently than controls. Our study shows that a water in oil (W/O) nanoemulsion formulation may provide a useful model for the effective delivery of chemical compounds into citrus phloem via a foliar spray for controlling citrus HLB.
authors.affiliation: College of Crop Science, Fujian Agriculture and Forestry University, Fuzhou, China; Indian River Research and Education Center, IFAS, University of Florida, Fort Pierce, FL, United States of America.
authors.forename: Chuanyu
authors.initials: C
authors.lastname: Yang
authors.affiliation: Indian River Research and Education Center, IFAS, University of Florida, Fort Pierce, FL, United States of America.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Powell
authors.affiliation: Horticultural Research Lab, USDA-ARS, Fort Pierce, FL, United States of America.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Duan
authors.affiliation: Horticultural Research Lab, USDA-ARS, Fort Pierce, FL, United States of America.
authors.forename: Robert
authors.initials: R
authors.lastname: Shatters
authors.affiliation: College of Crop Science, Fujian Agriculture and Forestry University, Fuzhou, China; Indian River Research and Education Center, IFAS, University of Florida, Fort Pierce, FL, United States of America; State Key Lab for Conservation and Utilization of Subtropical Agri-biological Resources, Guangxi University, Nanning, China.
authors.forename: Muqing
authors.initials: M
authors.lastname: Zhang
mesh_terms: D000890:Anti-Infective Agents / Q000008:administration & dosage*; D002957:Citrus / Q000382:microbiology*; D004655:Emulsions / Q000008:administration & dosage; D010935:Plant Diseases / Q000382:microbiology* / Q000517:prevention & control*; D018515:Plant Leaves / Q000187:drug effects / Q000382:microbiology*; D012230:Rhizobiaceae
chemical_list: D000890:Anti-Infective Agents; D004655:Emulsions