# Lactic Acid Bacteria as Biocontrol Agents against Potato (_Solanum tuberosum_ L.) Pathogens
## 3 Results and Discussion  
### Antimicrobial Activity of Lactic Acid Bacteria In Vitro  
The antimicrobial activity of lactic acid bacteria has already been widely described for foodborne bacterial pathogens such as _Escherichia coli_, _Salmonella_ spp., _Listeria monocytogenes_ and _Bacillus cereus_[27] as well as for fungal foodborne pathogens, e.g., _Aspergillus niger_, _Fusarium culmorum_, _Penicillium chrysogenum_[28]. In addition, the biocontrol of mycotoxins is of great interest to researchers since certain LAB strains demonstrated the ability to convert mycotoxins into fewer or non-toxic compounds [29; 30; 31; 32]. LAB activity against many potato pathogens is, however, underreported. This work is the first extensive study on potato biocontrol using lactic acid bacteria. The antimicrobial activity of 42 isolates and 58 collection strains of lactic acid bacteria (LAB) from the genera _Lactococcus_, _Leuconostoc_, _Lacticasebiacillus_, _Lactiplanttibacillus_, _Lecilatobacillus_ and _Lactobacillus_ were assessed against ten potato phytopathogens. A summary of the antimicrobial activity of LAB species is presented in Table 1. Detailed results of growth inhibition zones for each LAB strain and pathogen combination are listed in Table S1. The antimicrobial activity of LAB species varied depending on the pathogen and examined strain relationship. _Lactiplanttibacillus plantarum_ and _Lactobacillus acidophilus_ were the most widely represented a group of LAB species (47 and 19 strains, respectively). They exhibited a wide range of antimicrobial activity spectrum, including inhibition of both bacterial and fungi potato pathogens. Several studies reported antifungal activity of both _L. plantarum_ and _L. acidophilus_ species against _Fusarium oxysporum_[33; 34; 35; 36] and _Rhizoctonia solani_[33; 35; 37]. _Alternaria alternata_ was inhibited by _L. acidophilus_[38]. In our work, more than 90% of _L. plantarum_ strains inhibited the growth of _Alternaria solani_, _Alternaria tenissima_, _Colletotrichum cocodes_ and _Pectobacterium carootorum_ while the remaining pathogens were inhibited by at least 30% of the tested strains. All of the _L. acidophilus_ strains used in our research were active against _A. solani_, _C. cocodes_, _P. carootovorum_ and _Streptomyces scabiei_, and at least 35% of them inhibited the growth of the other selected potato pathogens (Table 2). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{10}{c}{**Number of Active LAB Species against Potato Phytopathogens**} \\ \hline \hline \multicolumn{10}{c}{**Lactococcus lactis [N = 9]**} & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 7 & 4 \\ _Leuconstoc mesenteroides_ [N = 9] & 1 & 1 & 1 & 2 & 1 & 3 & 1 & 1 & 9 & 6 \\ _Lactiostinellus casi_ [N = 2] & 1 & 1 & 0 & 0 & 0 & 2 & 1 & 0 & 2 & 2 \\ _Lactioblastitis acidophilus_ [N = 19] & 17 & 17 & 7 & 19 & 17 & 19 & 17 & 13 & 19 & 19 \\ _Lactiplanttibacillus plantarum_ [N = 47] & 41 & 42 & 15 & 45 & 44 & 44 & 35 & 31 & 44 & 33 \\ _Levilatobacillus brevis_ [N = 4] & 4 & 4 & 1 & 4 & 4 & 4 & 3 & 3 & 4 & 3 \\ _Lactiostinellus paracasi_ [N = 2] & 2 & 1 & 0 & 2 & 2 & 2 & 2 & 0 & 2 & 2 \\ _Lactiplanttiballus_ [N = 1] & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\ _Lactiobacillus_ [N = 6] & 5 & 6 & 4 & 6 & 6 & 6 & 2 & 5 & 6 & 2 \\ \hline \hline \end{tabular}  
N—number of tested strains belonging to this species.  
\end{table} 
Table 2: The antimicrobial activity of different species of lactic acid bacteria (LAB) cultivated on MRS medium against potato phytopathogens. Each of the _Lactococcus lactis_ strains was inactive against all fungal pathogens in our research. This LAB species has a homofermentative metabolism--lactic acid is the main product of sugar fermentation [39], while antifungal properties are most often described as the synergistic effect of acetic, propionic, phenyllactic and lactic acids [40; 41]. [PERSON] and [PERSON] [42] also reported no activity of _L. lactis_ against _R. solani_. Significant growth inhibition was, however, obtained in another study for _F. oxysporum_[43].