## 1 Introduction  
Plant diseases caused by microbial pathogens still pose a considerable threat to crop growth and yield and ultimately food security. At the world scale, yield losses due to fungal pathogens of the most commonly planted staple food crops (wheat, rice, maize, potatoes and soybean) accounted for 44.5 Mt in 2018 [1, 2]. In general, potential crop losses without crop protection for the above mentioned five crops are estimated to be in the range of 20 to 30% [2, 3]. Moreover, documented worldwide yield loss in cereals caused by microbial pathogens despite using crop protection accounted for \(\sim\)10% in wheat and \(\sim\)9% in barley for the time period 1996-1998 [4]. One possible means of crop protection is the application of seed treatment using chemical, biological or physical methods before sowing. Among them, chemical seed dressing using, e.g., fungicides provides almost complete and long-lasting protection against losses caused by seed-borne microbial pathogens. On the other hand, commercial application of those chemicals is decreasing because of toxicological effects on non-target organisms, the emergence of antifungal-resistant strains of especially pathogenic fungi, and environmental aspects along with potential effects on human health and public acceptance of usage (e.g., endocrine-disrupting features of azoles) (e.g., [5, 6, 7]). Thus, roughly 70% of the registered active ingredients of fungicide products are estimated to be prohibited in the EU because they meet cutoff criteria or might be listed as candidates for substitution in the near future [8]. A recent example is the ban of application from 2018 onwards for the seed fungicide Thiram, a dithiocarbamate fungicide which was widely used in rapeseed and legume seed treatment to prevent seed- as well as soil-borne infections. Alternatives for chemical seed treatment are needed to secure crop productivity and yield under high-risk situations (e.g., conducive soil properties and environmental conditions, as well as known load with soil-borne pathogens), especially in view of new emerging pathogens associated with climate change (e.g., [9; 10; 11]). One possible alternative is represented by biological seed treatments using antagonists or biological extracts. A recent meta-analysis across 210 publications on the effect of biological seed treatment on disease control until 2020 highlighted that the efficiency largely depends on the scale of observation and was significantly lower under field conditions compared to controlled environments with an average of \(\sim\)50% efficiency [12]. Moreover, the usage of small RNAs and short peptides in disease control is being explored, with major challenges in potential implementation including production costs, safety, stability and mode of delivery, as well as legal requirements [13]. Besides the above-mentioned methods, there is physical treatment, ranging from hot water or steam treatment of seeds (e.g., [14; 15; 16]) to methods like electron beam treatment (E-beam), which is already on the market [17], or cold atmospheric pressure plasma (CAPP), which is currently in the proof-of-concept stage. For post-harvest applications, CAPP has already been investigated in up-scaled environments under industrial-orientated circumstances (e.g., [18; 19; 20]). Plasma is considered the fourth state of matter and can be classified into thermal and non-thermal plasmas. Under laboratory conditions, CAPP can be produced at room temperature and atmospheric pressure by the excitation and ionization of gases with an externally applied energy source, e.g., electric and/or magnetic fields. Hereby, gas molecules are ionized or dissociated after electron and ion collisions with the background gas to create a plasma. Thus, plasma comprises different quantities of chemical species, charged particles, radicals, heat and UV radiation depending on the process parameters and the gas used (e.g., [21; 22; 23]). Exposure of the biological targets to CAPP can take place via two different methods.