Biocontrol potential of Bacillus velezensis lut-Y1: Antifungal lipopeptides against postharvest fungi Alternaria alternata and Penicillium expansum

Postharvest rot disease caused by plant pathogens severely affects the storage and quality of fruits and vegetables. Although chemical fungicides are commonly used for disease management, concerns over their environmental impact have driven the search for sustainable alternatives. The fermentation broth of strain Bacillus velezensis lut-Y1 isolated from the fruits of Lycium barbarum was extracted with methanol. The extract was purified via Sephadex LH-20 gel column chromatography and characterized using Fourier transform infrared spectroscopy, thin-layer chromatography and mass spectrometry. The influence of temperature and pH on the stability of the extract's antifungal effect was analysis by agar diffusion method. The antifungal effect of the extracts was also evaluated by artificially infecting tomatoes and apples with A. alternata and Penicillium expansum. The results showed that the extract obtained from the fermentation broth of B. velezensis lut-Y1 was a pale-yellow solid powder. The extract was comprised of two cyclic lipopeptides of distinct molecular weights, with m/z values consistent with iturin or surfactin analogues. Antifungal activity of the extracts was stable under 80 °C or pH 4 to 12 conditions. The extracts inhibit the growth of A. alternata by destroying the cell wall structure of hypha. Furthermore, the extract (2.5 mg/mL, 5 mg/mL, and 10 mg/mL) reduced lesion areas by 61.0%, 71.4%, and 85.3% in tomatoes inoculated with A. alternata, and by 33.4%, 74.8%, and 87.9% in apples infected with P. expansum. These findings demonstrate the potential of B. velezensis lut-Y1 as a biocontrol agent against postharvest rot in tomatoes and apples.