## 1 Introduction
Firstly, direct exposure when the sample is in direct contact with the plasma discharge. In this case, all plasma-generated components can interact with the sample. Secondly, indirect exposure, which involves treatment of an agent (gaseous or liquid) with CAPP and introducing this agent to the biological target, i.e., treatment of air with CAPP and transferring this plasma-processed air (PPA) to the biological target. Using the indirect configuration, not all CAPP components are able to interact with the target, e.g., UV light and short-lived reactive species are excluded (e.g., [24]). The efficiency of the microbial inactivation of CAPP strongly depends on the mode of exposure (direct or indirect), the configuration of the plasma reactor, exposure time to CAPP, process parameter used for CAPP treatment (e.g., input voltage, frequency, mode of operation, i.e., continuous, burst or pulsed), post-treatment storage time and the working gas used. Moreover, the type of microorganism (virus, bacteria, fungi, vegetative or generative status), the type of carrier of the microorganism (liquid media, agar plate, crop seed) and the location of the microorganism on the carrier, especially when using seeds (on the seed coat, inside the seed), are important factors which determine the overall efficiency of inactivation and ultimately disease reduction during growth of the crop under natural surroundings (e.g., [25; 26]). High efficiencies for inactivation of fungal pathogens using dielectric barrier discharges (DBD) were demonstrated in several publications, e.g., 80% reduction of viable spores of _Fusarium_ on rice seeds using an air DBD [27], 3 to 4 log\({}_{10}\) units reduction for _Aspergillus_, _Alternaria_ and _Fusarium_ on wheat seeds using a coplanar surface barrier discharge [28] and complete inactivation of _Fusarium_, _Trichotlecium_ and _Aspergillus_ on maize seeds using an air DBD [29]. Even though complete inactivation was reached, process parameters were detrimental for seed vitality in some cases, reflected in significant decrease in seed germination for longer treatment times in both above-mentioned cases. Efficiency of corona discharge (CD) treatments displayed similar results, with significant reduced seed germination at longer treatment times. Reduction of natural loads of molds and yeasts after CD treatment of broccoli seeds reached \(\sim\)1 log\({}_{10}\) unit and 1.5 log\({}_{10}\) units at 2 and 3 min treatment time, respectively, with a decrease in seed germination at 3 min treatment time of 32% [30]. Moreover, reduction of the natural fungal load (molds and yeasts) on seeds of rapeseed reached 2 log\({}_{10}\) units at 3 min treatment along with a decrease in seed germination by \(\sim\)30% at 3 min treatment time [31]. In our study, we investigate the inactivation efficiency of direct CAPP treatment using DBD [32] and CD [33] plasma sources and _Bacillus atrophaeus_ spores in order to evaluate the potential of direct CAPP exposure as seed treatment against sporulated forms of microbial pathogens, e.g., fungal or bacterial spores, in potential future pre-harvest application. Because unimpaired seed vitality after CAPP treatment has to be ensured in pre-harvest application, maximum germination was monitored simultaneously, along with the status of seed coat hydrophilicity. _Bacillus atrophaeus_ spores were chosen as test organisms for spore-forming pathogens on the seeds surface. This microorganism served as a proxy and is not a plant pathogen. The spores of this Gram-positive bacterium are commonly used as a bio-indicator for evaluating the efficiency of physical and/or chemical sterilization procedures in industry, biomedicine and sanitation [34]. The bacterium is ubiquitous distributed in the natural environment and no specific safety measures are needed due to its harmlessness.