Effect of foliar application of titanium dioxide on bacterial blight of geranium and Xanthomonas leaf spot of Poinsettia

Abstract

This study is the first report of using titanium dioxide (TiO2) to control Xanthomonas bacterial blight on geranium and leaf spot on poinsettia. Potted zonal geranium 'Patriot Bright Violet' and poinsettia 'Snowcap' were grown in a greenhouse and treated with a foliar spray of TiO2 at 25 and 75 mM, respectively, twice. Titanium-treated and control geranium plants were inoculated with Xanthomonas hortorum pv. Pelargonii and poinsettias were inoculated with Xanthomonas axonopodis pv. Poinsettiicola. The experiment was repeated once. The numbers of lesions on geranium leaves sprayed with TiO2 at 25 and 75 mM were 53% and 67%, respectively, less than in control plants in the first trial, but there were no significant differences among treatments in the second trial. Results on poinsettia, however, showed significant decrease in lesion numbers in both trials. Plants treated with TiO2 at 25 and 75 mM showed 85% and 93% reduction in lesions, respectively, in the first trial and 87% and 92% reduction in lesions in the second trial. No symptoms of phytotoxicity were observed. This study suggests that TiO2 has potential as an alternative to currently labeled products for controlling Xanthomonas bacterial blight in geranium and leaf spot on poinsettia.