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Zinc nanoparticles mitigate some fruit symptoms of Huanglongbing on citrus

Evan Johnson: University of Florida

<div>Huanglongbing (HLB) is a devastating citrus disease caused by the phloem-limited pathogen <em>Candidatus</em> Liberibacter asiaticus. HLB results in yield loss through small or misshapen fruit, preharvest fruit drop, and unripe, bitter juice. Delivery of bactericidal agents to citrus phloem is the greatest challenge in developing chemical therapies for HLB. Through a collaborative effort, we developed a novel zinc-based nanoparticle bactericide (Zinkicide™) using plant derived compounds. These particles are designed to be small enough (2-5 nm) to travel systemically through the phloem and to be metabolized by the plant after reaching their target, eliminating the concern of residues in the fruit. The synthesis protocol was designed to be simple and inexpensive for large quantity production. Zinkicide™ worked effectively as a soil drench to control citrus canker in a proof of concept greenhouse study demonstrating systemic efficacy. Multiple field trials in grapefruit and sweet orange resulted in increased fruit size from Zinkicide application. However, results suggest that application rates need optimization for dilution of active particles from systemic movement. Systemic efficacy in larger trees requires a combination of spray and soil drench. Disparities between canker (21-day applications) and HLB (28-day applications) trials suggest that residual efficacy is shorter than expected and clustering of applications may provide better efficacy than full year coverage.</div>