Biocidal Activity of Low Temperature Plasma to Xylella Fastidiosa

The quarantine bacterium Xylella fastidiosa was first detected in Salento (Apulia, Italy) in 2013 and caused severe symptoms in olives, leading to plant death. The disease, named Olive Quick Decline Syndrome (OQDS), is caused by the strain "De Donno" ST53 of the subspecies pauca of this bacterium (XfDD), which is spread by Philaenus spumarius. The epidemic poses a serious threat to the agricultural economy and the landscape, as X. fastidiosa infects several plant species and there is yet no recognized solution. Research on OQDS is focused on finding strategies to control its spread or mitigate its symptoms. In this context, we investigated the feasibility of using low-temperature plasma and plasma-activated water to kill bacterial cells. Experiments were conducted in vitro to test the biocidal effect of a Surface Dielectric Barrier Discharge plasma on bacteria. The results showed a high decontamination rate even for cells of XfDD embedded in biofilms grown on solid media. Application to trees requires protocols and tools that can reach the bacterium in the xylem vessels. Plasma Activated Water was tested as a biocidal agent that can move freely in the xylem network. Results in the liquid culture medium showed complete inactivation of XfDD cells and paved the way to test the strategy on infected plants.