| The goal of this dissertation was to investigate the potentials of ozone as a sustainable alternative to the soil fumigant methyl bromide and to synthetic pesticides. Three pathogens were selected for this research, given their economic importance, and the spectrum variety that they represent: Phytoparasitic nematodes, important pests that cause severe crop yield losses; Phytophthora sojae, a predominant soybean pathogen that causes root and stem rot, and pre- and post-emergence damping-off of soybean; and Fusarium oxysporum, which causes Fusarium wilt, an economically important disease in hydroponic systems.;Soil samples that were naturally infested with nematodes were treated with different levels of gaseous ozone at 21 °C and 5 °C. A medium level of ozonation (2.1 g O3 kg-1 for 10 min at a rate of ozonation 0.21 g O3 kg-1min-1) and low temperature (5 °C) resulted in 96% nematode inhibition. Regression analysis showed that nematode viability was a function of the level of ozonation (P = 5.1E-07) and the soil temperature (P = 4.4E-08; Adjusted R-square = 0.65).;Assays of artificially inoculated soil samples with P. sojae were treated with different doses of gaseous ozone. This study showed that a dosage of 0.47 g O3/kg soil, totally prevented root and stem rot disease symptoms caused by P. sojae..;Samples of conidial suspensions of F. oxysporum were treated with incremental doses of ozone from either oxygen feed with high gas-phase concentration (GPC) or air feed with low GPC. Trials resulted in non-viability of the pathogen at high ozone GPC with a dose of 0.84 mg O 3/L for 3 seconds. The optimal conditions for F. oxysporum treatment with ozone were high GPC (oxygen feed), and low temperature (5 °C).;Given these promising results, and since ozone degenerates quickly to oxygen, the findings of this research clearly indicate that ozone may be an efficient and sustainable alternative to methyl bromide and to: 1. nematicides in the treatment of nematodes in the soil, 2. fungicides in the inhibition of Phytophthora diseases in the soil, and 3. fungicides in the treatment of Fusarium wilt in hydroponic nutrient solutions. |
