Photocatalysis: Effect of Light-Activated Nanoscale Formulations of TiO2 on Xanthomonas perforans and Control of Bacterial Spot of Tomato

Paret, M. L., Vallad, G. E., Averett, D. R., Jones, J. B., and Olson, S. M. 2013. Photocatalysis: Effect of light-activated nanoscale formulations of TiO2 on Xanthomonas perforans and control of bacterial spot of tomato. Phytopathology 103:228-236. Protection of crops from bacterial diseases presents a continuing challenge, mandating the development of novel agents and approaches. Photocatalysis is a process where chemically reactive oxygen species are catalytically generated by certain minerals in the presence of light. These reactive oxygen species have the capacity to destroy organic molecular structures critical to pathogen viability. In this study, the antibacterial potential of photocatalytic nanoscale titanium dioxide (TiO2), nanoscale TiO2 doped (incorporation of other materials into the structure of TiO2) with silver (TiO2/Ag), and nanoscale TiO2 doped with zinc (TiO2/Zn; AgriTitan) was evaluated against Xanthomonas perforans, the causal agent for bacterial spot disease of tomato. In vitro experiments on photocatalytic activity and dose dependency were conducted on glass cover slips coated with the nanoscale formulations by adding a known population of X. perforans strain Xp-F7 and illuminating the cover slips under a visible light source. TiO2/Ag and TiO2/Zn had high photocatalytic activity against X. perforans within 10 min of exposure to 3 x 10(4) lux. Greenhouse studies on naturally and artificially infected transplants treated with TiO2/Zn at approximate to 500 to 800 ppm significantly reduced bacterial spot severity compared with untreated and copper control. Protection was similar to the grower standard, copper + mancozeb. The use of TiO2/Zn at approximate to 500 to 800 ppm significantly reduced disease incidence in three of the four trials compared with untreated and copper control, and was comparable to or better than the grower standard. The treatments did not cause any adverse effects on tomato yield in any of the field trials.