Aqueous Ozone in the Root Zone: Friend or Foe?

Aqueous ozone (O3(aq)) solutions were applied to the rockwool substrate of hydroponically cultured tomato and cucumber plants. Single applications of high concentration solutions (0, 5, 10, 15, 20 mg/L), as well as repeated application of lower concentration solutions (0, 2, 4, 6 mg/L), had no impact on leaf area and shoot dry weight accumulation. Repeated O3(aq) applications were also applied to cucumber plants inoculated with Pythium aphanidermatum.  Pathogen levels were significantly reduced in all treatments containing O3(aq). The reduction in pathogen numbers did not necessarily affect plant productivity.   Key words: Pythium aphanidermatum, irrigation water reuse, oxygenation, tomato, cucumber, rockwool, hydroponics, phytotoxicity.