Broad-spectrum antifungal activity of Lactiplantibacillus plantarum MYSVCF3 against phytopathogenic fungi

Lactic acid bacteria (LAB) are promising alternatives to chemical fungicides for the management of plant pathogenic fungi. However, their activity against diverse phytopathogens and the mechanisms underlying their antifungal effects remain insufficiently characterized. Here, we investigated the antifungal activity of fruit-derived Lactiplantibacillus plantarum MYSVCF3 against two phylogenetically distant phytopathogens, Fusarium oxysporum and Alternaria alternata . The antifungal effects of both live cells and cell-free supernatant (CFS) were evaluated. Live Lpb. plantarum MYSVCF3 significantly reduced mycelial biomass accumulation in both fungal species over time, while CFS inhibited fungal growth in a concentration-dependent manner. Conidial germination of both pathogens was strongly suppressed by treatment with either live cells or CFS. Fluorescence microscopy of propidium iodide (PI) stained hyphae showed increased PI fluorescence following CFS treatment suggesting compromised membrane integrity in both fungal species. The antifungal activity of CFS was retained after heat treatment and pH neutralization but was reduced following proteinase-K treatment suggestive of the involvement of both heat-stable and proteinaceous components. Organic acid profiling of CFS indicated citric acid (66.4%) and lactic acid (17.3%) as the major organic acids along with malic, succinic and pyruvic acids to a lesser extent. Further, individual organic acid assays revealed species-specific sensitivity. F. oxysporum was most inhibited by citric and lactic acids and A. alternata was more responsive to malic acid. The native-proportion acid mixture was less effective than the strongest individual acid. Hence it is a non-additive interactions. Overall, MYSVCF3 exhibits multifactorial antifungal activity through multiple complementary mechanisms under laboratory conditions. Further studies should validate these findings under plant-associated conditions.