Antifungal Activity of Fennel Essential Oil and Trans-Anethole against Sclerotinia sclerotiorum Isolated from Bean Plants and Evaluation of Phytotoxic Effects on Seed Germination

Introduction: The phytopathogenic fungus Sclerotinia sclerotiorum causes white mold disease in the common bean (Phaseolus vulgaris). This disease is disseminated through contaminated seeds, making the treatment of seeds with fungicides an effective control strategy. Methods: Given the lack of commercially available agroecological fungicides, we aimed to develop one based on the essential oil of fennel (EOF) and its primary compound, trans-anethole, using soybean oil as a diluent. Results: The EOF was characterized using gas chromatography-mass spectrometry (GC–MS), revealing that trans-anethole, limonene, and α-phellandrene accounted for a combined 89.8% of the total composition. The absolute concentration of trans-anethole determined via external standard was 76.72%. Discussion: The antifungal activity was evaluated in vitro using an S. sclerotiorum isolate obtained from infected P. vulgaris plants. EOF and trans-anethole were directly added to the culture medium. A minimum inhibitory concentration of 2000 μg·mL-1 was obtained in both cases. No phytotoxicity effects were observed in the germination test using P. vulgaris seeds treated with 40 mL·kg-1 of the diluted formulation at this concentration. Conclusion: These results highlight the potential of EOF and trans-anethole as environmentally friendly candidates for seed treatment against white mold disease.