## 2 Materials and Methods  
### Seed Material  
Seeds of _Hordeum vulgare_ L. (barley) accession Kosmos and _Tritcium aestivum_ L. (wheat) accession Informer were obtained from Ceravis AG (Rendsburg, Germany), while seeds of _Brussica napus_ L. (rapeseed) accession Atora were provided by NPZ Innovation GmbH (Holtsee, Germany) and seeds of _Lupinus angustifolius_ L. (lupine) accession Borgeing from Saatzucht Steinach GmbH (Steinach, Germany).  
Chemical pre-treatment was needed for barley seeds due to their high load of naturally occurring bacteria, which interfere with the inoculation and determination of viable spores after CAPP treatment. For sterilization before CAPP treatment, a 5% (\(p/v\)) sodium hypochlorite solution (NaCIO, Chemsolut Th. Geyer GmbH & Co. KG, Renningen, Germany) was applied to 16 g of barley seeds and incubated for one min while constantly shaking, with one repetition of this process. Following these two incubations, barley seeds were washed three times with 32 mL deionized water and dried under a laminar flow safety cabinet (Herasafe KS 12 class II, Thermo Scientific, Langenselbold, Germany) on Petri dishes for approximately two hours.  
Artificial Inoculation of Seeds with Bacillus atrophaeus Spores and Recovery of Viable Spores from Crop Seeds  
The sporulated form of _B. atrophaeus_ (DSM 675) originating from the German collection of microorganisms and cell cultures (DSMZ, Braunschweig, Germany) was used as a model in this study. A stock of spore suspension with concentration of 1 \(\times\) 10\({}^{9}\) CFU/mL was stored in sterile NaCl (0.85% \(w/v\)) at 7 \({}^{\circ}\)C for further use.  
Inoculation of seeds was carried out as described previously in [PERSON] et al. [35]. In short: a diluted spore stock culture with a density of \(\sim\)1 \(\times\) 10\({}^{7}\) CFU/mL was applied with a defined quantity for each gram of seed (i.e., 20 \(\upmu\)L for barley and wheat, 64 \(\upmu\)L for rapeseed, 30 g for lupine), followed by vigorously mixing for approximately 30 s to ensure an even distribution of the spore solution. Effective loading on the seed surface with viable spores accounted for 7.41 \(\pm\) 4.51 \(\times\) 10\({}^{4}\) CFU/mL for barley, 5.61 \(\pm\) 0.71 \(\times\) 10\({}^{5}\) CFU/mL for wheat, 2.36 \(\pm\) 0.39 \(\times\) 10\({}^{5}\) CFU/mL for rapeseed and 1.40 \(\pm\) 0.22 \(\times\) 10\({}^{5}\) CFU/mL for lupine seeds. Afterwards, inoculated seeds were dried for 30 min at room temperature in a laminar flow safety cabinet (Herasafe KS 12 class II, Thermo Scientific, Langenselbold, Germany) to allow the attachment of microorganisms on the seed surface. In preparation for treatment, seeds were transferred to pressure-resistant one-liter glass bottles (Duran, Mainz, Germany) using three replicates each with four technical replicates from each individual replicate.  
After plasma treatment (see below), recovery of spores from the seed surface was initiated by adding 40 mL of sterile soybean casein digest bouillon CASO broth ([PERSON], Karlsruhe, Germany) to the bottles and incubating them for 30 min on a horizontal shaker (150 rpm, PSU-20i, Biosan, Riga, Latvia) at room temperature, followed by centrifugation and re-suspension of the pellet. Re-suspended pellets were serially diluted and aliquots (10 \(\mu\)L) of appropriate dilutions were plated on CASO agar plates ([PERSON], Germany). Agar plates were incubated for 17 h at 30 \({}^{\circ}\)C (Binder BD 115, Tuttingen, Germany). Colony-forming units were counted manually. Finally, the logarithmic reduction in CFU was calculated using the difference in decimal logarithm of CFU/mL for CAPP-treated seeds and the CFU/mL determined for control samples without CAPP treatment. A second control was applied using gas flow through the reactors only (Cg), without igniting the plasma.