# Inactivation of the Plant Pathogen _Pythium ultimum_ by Plasma-Processed Air (PPA)
###### Abstract  
_Pythium_ species are saprophytic or facultative plant pathogens that cause a variety of diseases. Usually, chemical anti-fungal seed dressing is applied in the conventional pre-harvest for seed protection. Nevertheless, recent legislative rules have created a ban on certain agrochemicals. Therefore, alternative eco-friendly methods have to be identified to ensure healthy field emergence and seedling development. In this study, a proof-of-concept was performed on the inactivation of _Pythium ultimum_ Trow mycelia grown on potato dextrose broth agar (PBA) by plasma-processed air (PPA). Different plasma process parameters were applied using variation in gas flow of air through the microwave plasma generator and PPA exposure time. The PPA treatment was compared to the untreated and gas treated controls. The results showed a complete inactivation of _P. ultimum_ mycelia after the PPA treatment. Inactivation efficiency was independent of the gas flow parameter and even shorter exposure times resulted in complete inactivation. To fully evaluate the potential of PPA as a possible seed hygiene measure, tests regarding the inactivation of _P. ultimum_ after artificial inoculation onto seeds and/or studies using naturally infected seeds should be performed. This may be accompanied by monitoring the disease severity after the PPA treatment on a field scale. decontamination; plasma; plasma-processed air +
Footnote †: journal: Medical  
undergo extended dormancy and germinate under suitable conditions to produce single or multiple germ tubes. Finally, these germ tubes can form sporangia, thereby, recapitulating the asexual cycle of the pathogen [8]. Disease management of _Pythium_ encompasses mechanical, biological or physical methods, as well as adapting cultural practices such as tillage and crop rotation [9]. Chemical treatment is also widely applied as seed coating against _Pythium_ and other _Peronosporocytes_. These chemicals include mefenoxam/metalaxyl (acylanilide class) which have been shown to provoke resistance in _Pythium_[10]. The mode of inactivation of this fungicide class comprises inhibition of RNA synthesis in the fungi by interfering with the RNA polymerase, as well as a second mode of action, which involves a loss of cell permeability [11]. Furthermore, fungicides of the carbamate class, which include propamocarb, are used as an active ingredient in a number of commercial products, which have received user approval in the USA in 2021, but not in the EU. The carbamate class adversely affects membrane permeability, as detected by the leakage of cellular constituents out of cells mostly when treated during growth [12]. The fungicide captan (phthalimide class) is used in single, as well as in mixture application. Captan is also applied to manage multiple pathogens at the same time i.e., _Pythium_, _Fusarium_ and _Rhizoctonia_ spp. in soybean seed treatment [13]. The main mechanism responsible for the fungicide effect of this class is the reaction with proteic and non-proteic thiol groups in the microorganisms, which provokes the reduction of overall enzymatic activity, respiration, and many other physiological and morphological changes in fungi [14]. Nevertheless, the general use of pesticides can have adverse effects on human life, as well as on ecosystems [15], including specific effects of fungicides on soil bacteria, actinomycetes and non-pathogenic fungi [16; 17; 18]. This also encompasses the development of resistance of target organisms, especially when overusing azoles as generalized fungicides. Resistance in this case occurs via mutation of the azo target, the sterol 14\(\alpha\)-demethylase CYP51, a regulatory enzyme in the ergosterol biosynthetic pathway [19]. One potential alternative for seed treatment against fungal and bacterial pathogens is the application of cold atmospheric plasma using the direct or indirect exposure mode. It has been successfully tested on various crop species and pathogen types [20].