Plasma activated water: a new control clue against bacterial pathogens.

The bacterial plant disease control is nowadays limited to copper compounds, few resistance inducers and biocontrol agents, but prophylaxis still remains the most important control measure that is poorly explored. Experiments were carried out using sterile distilled water (SDW) treated by a nanopulsed dielectric barrier discharge. The electrodes of the plasma source consisted of aluminum foils, covered by 1 mm thick polystyrene as dielectric; one of the polystyrene dielectrics was shaped with edges in order to contain water to be treated Ten minutes treatment with a peak voltage of 19 kV and a pulse repetition frequency of 1,000 Hz induced in plasma activated water (PAW) the presence of nitrates, nitrites and peroxides, and a pH decrease. After the treatment, PAW was firstly assayed in in vitro experiments, using diffusion and dilution methods, to evaluate its direct efficacy against selected bacterial pathogens such as Erwinia amylovora, Pseudomonas syringae pv. actinidiae and Xanthomonas arboricola pv. pruni. PAW was then assayed in greenhouse trial to evaluate its ability to induce resistance in tomato plants against X. vesicatoria (Xv). PAW was applied at the root apparatus five days before and two days after Xv experimental inoculation; negative and positive controls were Bion®, streptomycin sulphate and SDW, respectively. In in vitro experiments, PAW did not show bacterial inhibition neither using diffusion nor dilution method. In greenhouse no phytotoxicity was detected on tomato plants, disease severity (DS) assessments highlighted a significant disease inhibition and a relative protection of approximately 35%.