# Low Temperature Plasma Strategies for
## 1 Introduction  
_Xylella fastidiosa_ (_X. fastidiosa_) is a xylem-limited gammaproteobacteriaam whose pathogenic mechanism relies on the occlusion of the xylem vessels. The bacterium lives in biofilm communities embedded in an exopolysaccharideacharide matrix from which clumps of cells are released to systemically colonize the infected plants. Infections of new plants are mediated by insect vectors which feed in the xylem, acquire the bacterium, and transmit it to new plants during successive feeding activities [1, 2]. The \"De Donno\" strain of _X. fastidiosa_ subspecies _pauca_ haplotype ST53 was discovered in late 2013 in the Salento Peninsula (Aptula region) in olive trees showing leaf scorching, extensive branch desiccations, and plant death [3]. Soon after, this bacterial strain was demonstrated to be the causal agent of these symptoms which were reconciled under the name of Olive Quick Decline Syndrome (OQDS) [3]. While affecting the two major autochthonous olive cultivars Ogliarola salentina and Cellina di Nardo, this strain has been found infecting 595 plant species and in several cases without showing symptoms [4]. The finding of _X. fastidiosa_ in this new environment and infecting primarily olive stimulated several research programs which led to the description of the epidemiology of the infections in the epidemic area in the Salento Peninsula, the identification of _Philaneus_spumarius_ as the insect vector, the genomic of the bacterium and the olive response to the infections [5]. The _X. fastidiosa_ epidemic in southern Italy is slowly expanding north to the southern portion of Apulia. However, besides Italy, where a subspecies _multiplex_ strain of _X. fastidiosa_ was found in Tuscany [6], other strains were discovered in France [7], Spain [8; 9], Portugal [10] and recently in Israel [11], which highlights the severe threat that this quarantine bacterium poses to the Mediterranean agriculture. Generally, bacterial cells are inactivated by physical processes, such as heat and gamma radiation, and chemical processes, such as ethylene oxide, that are not suitable for curing _Xylella_-infected plants. Heat can cause irreversible damage to the plant; ethylene oxide is highly inflammable and toxic, and radiation processes require isolated sites and the safety of operating personnel and can induce DNA damage. Such disadvantages drive research for a novel, highly efficient sterilization process. Among the microbial inactivation strategies, non-thermal atmospheric pressure plasma has achieved increased attention in biology, medicine [12; 13; 14] and the agri-food industry [15; 16; 17]. Low-Temperature Plasma (LTP) has potential advantages over conventional methods, such as its controllable level of toxicity, low process operational costs, short treatment time at almost room temperatures and applicability to a wide variety of goods [18; 19; 20; 21]. Nevertheless, it must be pointed out that plasma characteristics need to be properly defined and a careful selection of device design and system operating parameters are needed to obtain a positive effect on the treated samples [22; 23; 24]. Atmospheric air LTP is an excellent source of several antimicrobial agents in the gas phase. [25]. The reactive species produced include electronically and vibrationally excited oxygen O\({}_{2}\) and nitrogen N\({}_{2}\); reactive oxygen species (ROS), such as atomic oxygen O, singlet oxygen \({}^{1}\)O\({}_{2}\), superoxide anion O\({}_{2}\) and ozone O\({}_{3}\) and, if humidity is present, H\({}_{2}\)O\({}^{+}\), OH\({}^{+}\) anion, OH radical or H\({}_{2}\)O\({}_{2}\)[26]; and reactive nitrogen species (RNS), such as atomic nitrogen N, nitrogen metastable state N\({}_{2}\)(A) and nitric oxide NO. Target organisms are either directly exposed to the plasma-produced ROS and RNS together with UV light and/or pulsed electric field produced by the plasma.