# Lactic Acid Bacteria as Biocontrol Agents against Potato (_Solanum tuberosum_ L.) Pathogens
## 3 Results and Discussion
### In Situ Test of Biocontrol Potential of L. plantarum KB2 LAB 03 against Pathogens on Potatoes  
The LAB antimicrobial activity against plant pathogens is underreported during vegetable and fruit storage. _L. plantarum_ prolonged the shelf-life of kiwifruits contaminated with _Botrytis cinerea_ for two weeks [53]. This species was also effectively used to delay the development of _Fusarium graminearum_, _B. cinerea_ and _Rhizopus stolonifer_ in storage cucumbers [37]. More reports concerning pot and field experiments reveal the influence of LAB on plant growth. [PERSON] et al. [54] described the antifungal effect of _Lactobacillus_ sp., _Pediococcus acidilactici_ and _Pediococcus pentosaceus_ treatment in a pot experiment for strawberries inoculated with _Fusarium_ sp., _Rhizoctonia_ sp., _Botrytis_ sp. And other moulds. Several studies reported plant growth-promoting properties of lactic acid bacteria for tomatoes [55] and spring wheat [56] while facing pathogen infection. The in situ antimicrobial activities of _L. plantarum_ KB2 LAB 03 cultured on A100 M100 acid whey-based medium and laboratory MRS medium against the ten potato pathogens were assessed on seed potatoes. The results are presented in Table 4 and Figure 8.  
Figure 6: Fermentation by-products of the _L. plantarum_ KB2 LAB 03 cultured on A100 M100 acid whey-based medium. a–d—results with different letters are significantly different (Tukey’s test, \(\alpha=0.05\)). Figure 7: RI chromatogram of investigated by-products of the _L. plantarum_ KB2 LAB 03 cultured on A100 M100 acid whey-based medium. 8-lactic acid; 9-acetic acid; 10-propionic acid; 13-ethanol; 15-valeric acid. To the best of our knowledge, this is the first report of in situ experiments on potatoes that confirms the antimicrobial activities of lactic acid bacteria against _Fusarium_, _Alternaria_, _Phoma_, _Colletotrichum_, _Rhizoctonia_, _Pectobacterium_ and _Streptomyces_ phytopathogens. It was revealed that _L. plantarum_ KB2 LAB 03 cultured on an A100 M100 acid whey-based medium reduced the development of both bacterial pathogens as well as six out of eight fungal species (Table 4). _F. oxysporum_ and _F. sambucinum_ were found to be resistant, even though the in vitro assay showed the inhibition of these fungi by tested _L. plantarum_ KB2 LAB 03 culture (Tables 3 and 4). [PERSON] et al. [33] and [PERSON] et al. [35] research reported plant growth promoting activities of _L. plantarum_ on tomato seeds in pot trials, while the seeds were infected with _F. oxysporum_. However, these studies did not assess the reduction of pathogen development. Cultivation of LAB selected strain on acid whey-based medium ensured the same or more effective inhibition of potato pathogens than on MRS \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Phytopathogens**} & \multicolumn{3}{c}{**Inhibition of Potato Infestation [\%]**} \\ \cline{2-3}  & **A100 M100 Acid** & **MRS Medium** \\  & **Whey-Based Medium** & **400** \(\pm\) 5 \\  & **Phoma exigua** & 700** \(\pm\) 0 * \\  & **Pectobacterium carotovorum** & 900** \(\pm\) 10 \\  & **S streptomycin csubiei** & 850** \(\pm\) 0 * \\ \hline \end{tabular}
\end{table} 
Table 4: Inhibition of potato seed cv. Impresja infestation treated with _L. plantarum_ KB2 LAB 03 cultured on A100 M100 acid whey-based medium against potato phytopathogens. Figure 8: Inhibition of _Streptomyces scabiei_ (**A,B**) and _Pectobacterium carotovorum_ (**C,D**) infestation of potatoes cv. Impresja treated with _L. plantarum_ KB2 LAB 03 cultured on A100 M100 acid whey-based medium. (**B,D**)—control samples; (**A,C**)—tested samples. medium (with the exception of _P. exigua_). These results correlated with characteristics of fermentation by-products (Figures 2 and 6), where A100 M100 acid whey-based medium post-culture fluid of _L. plantarum_ KB2 LAB 03 contained a significantly higher concentration of acetic, propionic acid and ethanol than MRS post-culture fluid od selected LAB strain.