Bacterial spot of tomato is caused by various Xanthomonas strains. X. perforans, which is the dominant species for bacterial spot of tomato in Florida is tolerant to traditional Copper (Cu)-based bactericides. Cu in combination with Mn is the only choice available to growers, making disease management extremely challenging. In this research project, we introduce a concept of delivering locally more than one bactericidal agents through a nanoparticle delivery system (called hereafter Locally Systemic Pesticide, LSP). The entire synthesis of LSP particles was done in a modular fashion, producing well-defined set of nanoparticles of three different sizes (~50 nm, ~200 nm and ~500 nm). Particle size, shape and morphology of the LSP particles were characterized using dynamic light scattering (DLS) and electron microscopy (EM) techniques. HRTEM measurement at high-magnification on shell revealed the formation of ultra-small size (&lt;10 nm) Cu nanoparticles with +2 and +1 multi-valence oxidation states. Release kinetics of Cu and Quat actives from LSP particles were studied, and smallest size of LSP particles demonstrated higher release of both Quat and Cu actives compare to larger sizes. Phytotoxicity of LSP particles was evaluated against ornamental Vinca plants and the evaluation was done at 72h post-foliar spray. LSP particles were found to be non-phytotoxic as high as 1,000 µg Cu/mL and 250 µg Quat/mL, while Quat only demonstrated signs of phytotoxicity at 250 µg/mL. This suggests that silica serves as a diluent as well as a barrier for Quat minimizing their direct interaction with the plant tissue. In-vitro antimicrobial efficacy of LSP particles were tested against multiple bacteria strains as well as Cu-tolerant strains. MIC of LSP particles were found to be between 2-8 µg Cu/mL. Colony forming unit (CFU) assays were carried out to understand time and concentration needed to kill Cu-tolerant strains of X. perforans. All LSP particles completely killed the bacteria as low as 5 µg Cu/mL at 4 h time point, and interestingly the smallest size of LSP particle killed at 1 µg Cu/mL at 4h time point. Commercial control Cu hydroxide and reagent grade Cu oxide demonstrated efficacy as high as 100 µg Cu/mL at 24h time point. Due to unique design and high antimicrobial efficacy, LSP particles could be a bactericide of choice for growers to manage both Cu sensitive and tolerant strains of pathogenic bacteria, while potentially decreasing Cu spray at the field.

Development of nanotechnology enabled locally systemic pesticide (LSP) particles

2019 Spring National Meeting

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