Potential of lactic acid bacteria in biocontrol of Aspergillus niger, Penicillium chrysogenum and Fusarium graminearum in culture media and natural substrate

Adverse storage conditions impair the quality of stored grain, contribute to the growth and propagation of the fungi leading to an even greater deterioration of the grain quality. Antifungal biopreparations can help preserve grain quality. Lactic acid bacteria (LAB) and their metabolites with antifungal properties can potentially be used in storage conditions or for the decontamination of stored products. The aim of this study was to determine the antifungal activity of Lactobacillus casei, Lactobacillus brevis and Leuconostoc mesenteroides on the inhibition of mycelial growth of pathogenic fungi Aspergillus niger, Penicillium chrysogenum and Fusarium graminearum. The biocontrol potential of LAB against fungi was tested under laboratory conditions in culture media as an ideal substrate for fungal growth and wheat grains as a model of natural substrate. A liquid culture media (MRS broth) was inoculated with cells or cell-free supernatants (CFS) of each LAB species and the fungal spores. The fungal growth was evaluated by measuring the increase in mycelial biomass after 7, 14, 21 and 28 days of incubation. The second antifungal assay was performed on the wheat grain treated with LAB CFS and inoculated with fungal spores. Biopreparation containing cells or CFS of all LAB species significantly inhibited the fungal growth of P. chrysogenum (mean inhibition 69-75% LAB cells and 80-81% LAB CFS) and F. graminearum (mean inhibition 60-83% LAB cells and 83-88% LAB CFS) in the culture media. In the treatment with wheat grain, the CFS of all the tested LAB species significantly inhibited only the growth of F. graminearum (83-90% mean inhibition). There is inconsistency in the efficiency of LAB preparations when comparing assays. The results indicate that media used in the experiment affect the activity or tolerance of the tested bacteria and fungi. L. casei, L. brevis and L. mesenteroides proved their antifungal properties in the culture media and natural substrate. F. graminearum was the most susceptible, and A. niger was the most tolerant to treatments with LAB cells and LAB CFS. More research is needed to reveal the mode of action of the LAB against phytopathogenic fungi in different conditions for their application on stored grains.