## 4 Discussion
Soil is the environment on which agricultural production depends, with many biological, chemical, and physical interactions involving microorganisms [86]. In the competition process, the microorganisms contained in the BCAs reduce the phytopathogenic inoculum or inhibit their biological activity [83; 87]. _Bacillus subtilis_ bacteria are most commonly used in plant protection because of their high spore-forming capacity and their ability to adapt to different soil conditions [82]. Moreover, these Gram-positive sticks produce numerous compounds and bioactive metabolites (e.g., ribosomal peptides, polypeptides, volatile compounds) with strong antimicrobial properties [88]. The preparation Serenade ASO that was used in our study and based on _B. subtilis_ str. QST 713 (BCABs) ensured the best phytosanitary condition of the potato tuber surfaces, irrespective of the growing season. The effectiveness of BCABs in the diseases analyzed was between 36.7% for _S. scabies_ and 47.7% for _R. solani_ (Figure 4). _B. subtilis_ QST 713 colonizing the roots not only activates the natural defense mechanisms of plants but modulates their growth. The resulting increases in the yield of potato tubers were, on average, 8.7%, corresponding to 3.6 t-ha\({}^{-1}\) (Figure 5). [PERSON] et al. [89] state that plants treated with _Bacillus subtilis_ Bv17 strain produce larger yields due to the increase in the weight of the tubers, which results from an increase in dry matter, starch, protein content, and reducing sugars. When introducing a mixture of _B. subtilis_ and _Trichoderma harzianum_ into the soil, [PERSON] et al. [90] obtained 23-32.2% yield increases and a 30.6-46.1% reduction in common scab severity. [PERSON] et al. [91] report that _Bacillus amyloliquefaciens_ species also reduces the common scab severity by 50%. An even stronger (76%) suppression of _S. scabies_ was found under the influence of _Bacillus altitudinis_[92]. There is little information available in the literature about black scurf and silver scurf suppression by _B. subtilis_. In German studies, _B. subtilis_ reduced the share of tubers with black scurf symptoms by 50% and common scab by 67% [93]. In contrast, the Tunisian strain _B. subtilis_ V26, under greenhouse conditions, reduced the occurrence of black scurf by 63% [94]. The representative of the kingdom of Chromista (class Oomycetes), _Pythium oligandrum_, is one of the best-known organisms used in plant protection for the longest [43; 44; 95; 96]. According to [PERSON] [97], _P. oligandrum_ contributes to an increase in the soil population of antagonists, which reduces the density of many important pathogens, including _R. solani_. In addition, it induces resistance to biotic and abiotic stress in plants [98]. In the tests carried out, independent of the growing season, Polyversum WP (BCAPo) preparation, which contains spores of this organism, applied to the soil and onto the surface of seed potatoes showed the greatest efficacy (E = 42.7%) against _R. solani_, which means that the mean DSI was 24.3% lower than in the control sample. Similar protective effects (E = 45.3%) were obtained after the treatment of potato tubers with this preparation and a single application onto the plants [99]. In light of the study conducted, the efficacy of BCAPo is lower against _H. solani_ (E = 36.3%) and _S. cables_ (29.7%) (Figure 4). This is confirmed in the study by [PERSON] and [PERSON] [100], in which _P. oligandrum_ efficiency against silver scurf was estimated at 6.8-16.8%. Treatment of seed potatoes and the foliar application of _P. oligandrum_ protect the plant also against other important pathogens such as _Ptytophthora infestants_, _Alternaria alternata_, and _A. solani_[3]. Organic farming systems use preparations that are currently included in the category of microbial soil additives (MSADs), the first product of which is effective microorganisms (EM).