## 4 Discussion
Altogether, alteration of plasma process parameters (input voltage, duty cycle, working gas, gas flow, exposure time, pots-storage time) might increase the detected efficiency in our study and might be pursued in a follow-up study. In general, spore inactivation by direct CAP, from artificially inoculation onto seed surfaces to natural load and to application of pure spore solution, has been extensively demonstrated (e.g., [25; 26]). [PERSON] et al. [36] observed higher plasma inactivation levels of fungal load for smoother corn seeds compared to barley seeds, which was also detected in our study. Moreover, factors such as density of the pathogen loading and spatial distance, as well as the location of the microorganism towards the plasma source, play a role in determining the overall efficiency of inactivation on surfaces, as well as for processes such as pulsed electric fields [37]. Using a DBD with atmospheric air as a working gas, inactivation of a natural fungal of wheat seeds was determined, reaching maximum values of \(2.5\log_{10}\text{CFU}/\text{g}\) seeds after 20 min of direct treatment and 24 h of post-treatment retention time, which was accompanied by a reduction in seed germination of 85% [38]. In the same study, a shorter exposure time of five minutes and 24 h post-retention time led to an inactivation of \(0.9\log_{10}\text{CFU}/\text{g}\) without negative effects on seed germination. This is in line with results from our study, where CAPP exposure times < 20 min led to inactivation of \(0.96\log_{10}\text{CFU}/\text{mL}\) in wheat seeds for the volume-DBD treatment, but with argon as the working gas, there was no impairment of seed germination. Moreover, a nearly complete reduction of _Fusarium culmorum_ spores on wheat and barley seeds was accompanied by a decrease in seed germination of -54% for treatment times > 120 s using an atmospheric pressure diffuse coplanar surface-DBD with ambient air as a working gas [39]. In the field of post-harvest treatment of spices, inactivation of _B. atrophaeus_ spores on black pepper using a radio frequency (RF) plasma jet resulted in a reduction of viable spores of \(1.3\log_{10}\text{CFU}/\text{g}\) peppercorns after 15 min of exposure [40]. Here, viability of seeds was not the target and was not studied. Using the same microorganism in its sporulated form as in our study, _B. atrophaeus_, [PERSON] et al. published a reduction of \(3.1\log_{10}\text{after five minutes of exposure using a pure spore solution which was semi-dry inoculated onto Petri-dishes and treated with a non-thermal RF-driven plasma jet with pure argon as a working gas [41]. The higher inactivation of spores compared to our study resulted from the type of plasma source used, as well as the media in which the spores were treated. Similar, high levels of inactivation of dried spore solution of _B. atrophaeus_ on glass slides treated with an atmospheric-pressure Ar/O\({}_{2}\) plasma jet were reached, with complete inactivation after 40 s of exposure [42]. Efficient inactivation was achieved using pure cultures of spores and argon as a working gas for CAP treatment due to the relatively higher amounts of reactive nitrogen and oxygen species (RONS), especially hydroxyl radicals (OH\(\bullet\)), which might be quenched in the other process gas compositions using pure or mixtures of oxygen, nitrogen or helium (e.g., [41]). Argon as a working gas was also used in our study. Some admixture of air (including oxygen) might also have occurred because the two reactors were not airtight. Commonly detected reactive chemical species of the plasma sources used in this study have been previously published by [PERSON] et al. [32; 33]. Due to its configuration, ambient air was able to diffuse into the reactor of the volume-DBD. Thus, reactive oxygen and nitrogen species (RONS) were produced in the discharge after admixture inside the reactor with weak emission of nitrogen oxide, hydroxyl radicals and molecular dinitrogen, as well as strong argon emission, with preferred energy transfer to oxygen.