Electrifying greenhouse agriculture: Cold atmospheric pressure plasma technology for Pythium ultimum control

Hydroponic growth of food plants in greenhouses is of rapidly increasing importance to assure future autonomy of food supply, especially in harsher climate zones. Greenhouse culture yields are drastically reduced by pathogenic microorganisms that cause root rot in plants. In Canada, the fungus Pythium ultimum, which can survive harsh winter conditions, has a particularly large impact on food production. In this work, we present cold physical plasma treatment of liquids with a gliding arc plasma as a novel approach for combating pythium growth in liquid media. This study is based on exploring air or other N₂ + O₂ mixtures as a parameter to identify which plasma treatment is best suited for its anti-fungal activity in different media. If sourced from renewable energy and water, the proposed treatment is intrinsically sustainable. 3 media conditions are explored: first distilled water, to identify the production of highly reactive oxygen species (ROS) and reactive nitrogen species (RNS). Second, an inoculated distilled water is used in conjunction with an ELISA assay as a quick response indicator. Third, a Sabouroud 2 % dextrose broth, is used as a culture media in which oomycetes are grown subsequent to plasma treatment, and hyphal mass is compared between untreated and treated samples. Extracting a subset of 80+ chemical reactions from the available literature and databases, a reaction scheme is proposed accounting for liquid-vapor equilibria (through Henry’s coefficients) and reaction rate analysis. The most promising plasma treatment condition was found to be using a 95 % N₂: 5 % O₂ gas mixture with a treatment time of 30 min, reducing hyphal mass growth from 1.8 g to 0.4 g over 1 week in Sabouroud broth. The pythium degradation process was observed through scanning electron microscopy (SEM) analysis, showing that Sporangium or oogonia containing structures that terminate the pythium’s hyphae have been broken and significantly reduced after plasma treatment.