Cyclic Dipeptide Cyclo( l -Phe- l -Pro) Derived from Beauveria bassiana Exhibits Stronger Antifungal Activity than Beauvericin Against Fusarium oxysporum

Fusarium oxysporum f. sp. lycopersici ( Fol ) is a destructive soil-borne pathogen responsible for major global losses in tomato production, within a context of increasingly constrained fungicide use in intensive farming systems. Sustainable alternatives to chemical fungicides are urgently needed, and microbial secondary metabolites represent a promising source of antifungal compounds. This study explores the antifungal potential of secondary metabolites produced by a natural isolate of Beauveria bassiana ( Bb 758) previously reported to exhibit strong biocontrol activity against Fol . LC-HRMS metabolomic profiling revealed a chemically diverse metabolite profile dominated by amino acid-derived compounds, peptides and alkaloids. Purification of the crude extract by column chromatography and reverse-phase HPLC yielded beauvericin and several 2,5-diketopiperazines as the main bioactive constituents. These compounds were identified by NMR and LC-HRMS analyses. The antifungal activity of beauvericin (BEA), cyclo( l -Phe- l -Pro) (CFP) and fractions was evaluated against spore germination and germ tube development of Fol . BEA exhibited dose-dependent but limited activity, showing significant inhibition only at high concentrations (100 μg mL −1 ). In contrast, CFP showed significantly higher antifungal activity than BEA, inhibiting both germination and germ tube formation at concentrations as low as 10 μg mL −1 . These results identify CFP as a promising antifungal compound targeting the early infection stages of Fol and highlight fungal-derived diketopiperazines as candidate molecules for sustainable disease management strategies.