Cell-free supernatant crude extracts of mold-competing bacteria protect peanut crops against yellow mold disease caused by Aspergillus flavus AF1

Abstract

Bacillus sp. 16060 (Bacillus subtilis group), Serratia marcescens SE1, and S. marcescens SE2, isolated from malted barley and peanut seedlings with yellow molds, inhibited the growth of Aspergillus flavus AF1 on various culture media and peanut seeds. Ethyl acetate extracts from these bacteria, cultured in Nutrient Broth (NB) and Peptone Glycerol Broth (PGB) with A. flavus AF1 biomass as an inducer, exhibited fungicidal properties. The Minimum Fungicidal Concentration was 100 μg/ml for strain 16060 and 250 μg/ml for strains SE1 and SE2. UHPLC-ESI-QTOF/MS and GNPS analysis revealed many unsaturated fatty acids in the crude extract of Bacillus sp. 16060, whereas polyketides were primarily identified as metabolites from two Serratia marcescens strains. All three crude extracts contained cyclic lipopeptide of the icosalide family. These extracts, with biosurfactant properties, effectively reduced yellow mold Disease incidence on peanut seeds from 93.3% to 65.0% after seed treatment. The Disease severity index for treated seeds ranged between 0.29 and 0.39, compared to 0.67 for untreated seeds. The Disease control efficacy of strain 16060's crude extract matched commercial fungicides, outperforming those of strains SE1 and SE2. All extracts effectively protected peanut seedlings from yellow mold disease, promoting vigorous growth. There was a 2.96–3.25 fold rise in Germination percentage, 4.61–4.80 fold in Vigor index, and 2.45 fold in biomass relative to the control. Hence, antifungal crude extracts derived from the mold-competing bacteria Bacillus sp. 16060, S. marcescens SE1, and S. marcescens SE2 may serve as multicomponent bacterial fungicides for peanut cultivation, providing protection against phytopathogenic mold.