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Development and evaluation of nano-materials for management of copper-tolerant Xanthomonas perforans causing bacterial spot of tomato

Mathews Paret: North Florida Research and Education Center, University of Florida

<div>Bacterial spot of tomato is caused by four <em>Xanthomonas</em> sp. (<em>euvesicatoria, gardneri, perforans and vesicatoria</em>) and is one of the topmost bacterial disease of relevance to tomatoes in the U.S and worldwide. Currently all strains in Florida are <em>X. perforans</em> and copper-tolerant, leaving few effective compounds for disease management. Thus, finding alternatives to copper bactericides is critical for the tomato industry in Florida. Studies were undertaken from 2010-2017 to develop and evaluate the antibacterial activity of two photocatalytic (light-activated) nanomaterials (titanium dioxide doped with zinc -TiO<sub>2</sub>/Zn or silver - TiO<sub>2</sub>/Ag), a silver-dsDNA-graphene oxide composite, and three copper composites (core-shell copper - CS-Cu, multi-valent copper - MV-Cu, and fixed quaternary ammonium copper -FQ-Cu) as potential alternatives to copper bactericides. All the tested nano-materials demonstrated high antibacterial properties against copper-tolerant <em>X. perforans</em> strains. These nano-materials were also shown to significantly reduce bacterial spot disease severity in greenhouse and/or field studies compared to non-treated controls and activity was similar or better than copper-mancozeb, the grower standard. Nanomaterial composition and properties play important roles in plant safety as well as performance in greenhouse and field conditions. However, successful commercialization of nanomaterial containing bactericides would require clearance of potential regulatory issues.</div>