Characteristics of Plasma Activated Water Produced by Air Plasma Torch and Inhibition Efficacy on Grey Mould

Grey mold is one kind of plant disease caused by Botrytis cinerea. This fungus has a broad host range of over 200 plant species like cucumber, tomato, grape, etc., inducing food losses during both pre- and postharvest stages of the food supply chain. Fungicide application remains one of the most common methods to control B. cinerea. However, the abuse of fungicides and pesticides raises concern about drug residues both in food and environment. Low-temperature plasma (LTP), as well as its activated medium, have shown inactivation ability against various pathogens in the bio-medicine field. Plasma activated water (PAW) is considered as an economic method to control fungal pathogens in agriculture by extending the lifetime and diffusion of reactive oxygen and nitrogen species from LTP. In this study, PAW was produced through the interaction between 200mL deionized water and an air plasma torch. The torch was fed by 1.5L/min air flow from a coaxial needle-cylinder electrode, driven by a 40kHz high voltage source with about 65W power input. The properties of PAW were featured by temperature, pH, oxidation-reduction potential (ORP) and electrical conductivity (EC). Inhibition efficacy of PAW on fungi was evaluated by mycelial growth on the potato dextrose agar plate. The results show that temperature, ORP and EC of PAW increase to 34.8°C, 217mV and $170 \mu \mathrm{S} / \mathrm{cm}$ while pH decreases to 3.1 after 10 min activation, respectively. The in vitro results show that inhibition rate of 10min-activation PAW on B. cinerea is 75.7% after 72h incubation by measuring the area of hyphae on the medium. This research provides a potential alternative to fungicides for eco-friendly prevention of grey mould.