## 4 Discussion
### Effect of Ozone-Induced Free Radical Solution on Microbial Killing Mechanism and Disease Control  
As the concentration of the ozone-induced free radical solution increases, so does the quantity of the free radicals, leading to a higher sterilization rate. Under consistent experimental conditions, an extension in treatment time results in an upward trend in bactericidal efficacy. Increasing the mass concentration of the ozone-induced free radical solution intensifies damage to the cell structure of _Bacillus subtilis_, manifesting as cracks, voids, depressions, thinning and rupture of the cell wall, and the formation of gas chambers within the cells. The observed outcomes stem from the high oxidative reactivity of free radicals, capable of interacting with various cellular molecules, with these outcomes including lipid peroxidation, protein damage, and nucleic acid oxidation, thereby causing damage to bacterial cell structures and functional loss. Furthermore, within a specific concentration range, as the TRO mass concentration increases and the exposure time extends, the quantity of free radicals capable of disrupting microbial cell structures rises, consequently enhancing the killing efficacy and extent of structural damage to _Bacillus subtilis_. Oxidative stress induced by these free radicals frequently triggers oxidative reactions in harmful microorganisms, compromising their cell membrane integrity and energy metabolism enzymes, leading to structural and physiological dysfunction in bacteria and ultimately causing their physiological activities to cease [44]. Additionally, these findings elucidate the inhibitory impacts of the ozone-induced free radical solution on harmful microorganisms and its underlying microbicidal mechanism.  
The 1.5 mg/L ozone-induced free radical solution and 5% imidalcoprid demonstrated effective control over pests in leafy greens, reducing pest severity from grade 1 to grades 3 and 4, respectively, thereby offering protection to Chinese cabbage. The application of ozone-induced free radical solution can damage certain physiological organs of pests, leading to disruptions in their physiological activities. This ultimately results in the effective inhibition of pest populations [15]. Xu applied ozone water for Plutella xylostella management, achieving a control efficacy of 76.4% and a larvae reduction rate of 59.3% [45]. Collectively, these findings underscore the potential of utilizing ozone-induced free radical solutions as alternatives to conventional chemical pesticides.  
Research on the ozone-induced free radical solution indicates that plants' physiological responses to this solution vary according to crop species and external environmental factors. An excessively high concentration of the ozone-induced free radical solution can inhibit rice and other crops. The control effect of the ozone-induced free radical solution varies across different plant diseases. Recent studies have demonstrated that the ozone-induced free radical solution is effective in controlling cucumber powdery mildew, tomato nematodes, and other diseases [46]. Future research should further investigate the effects of varying crops, growth cycles, spray volumes, methods, timing, and environmental parameters on crop growth, disease control, fruit quality, and yield after ozone-induced free radical solution application. Additionally, expansion to include disease prevention in outdoor vegetables, fruits, plants, and flowers is warranted [47; 48].