Antifungal efficacy and characterization of the dose-response relationship of Eucalyptus globulus essential oil against Fusarium sp. and Colletotrichum sp. in postharvest fruits of Theobroma cacao

Abstract

Postharvest fungal rot caused by Fusarium sp. and Colletotrichum sp. accounts for between 15 and 50% of global Theobroma cacao fruit losses, and conventional synthetic fungicides carry widely documented toxicological and ecological risks. This study evaluated the antifungal potential of Eucalyptus globulus essential oil (EO)  as a biofungicide for postharvest cocoa management. The EO was obtained by steam distillation (yield: 1.82 ± 0.14% w/w) and was chemically characterized by gas chromatography coupled to mass spectrometry (CG-MS), confirming a chemotype dominated by 1,8-cineole (72.4 ± 1.7%). In vitro antifungal activity  was assessed at five concentrations (0.02–6.30% v/v) using the agar dilution technique; radial growth inhibition percentage (PICR) data were fitted to a four-parameter logistic model (4PL), obtaining EC50 values of 0.96% v/v (95% CI: 0.72–1.28) for Fusarium sp. and 0.36% v/v (95% CI: 0.25–0.52) for Colletotrichum sp. In vivo postharvest efficacy  was determined in inoculated cacao fruits by measuring the daily lesion area (cm²) for 15 days and integrating it into the Area Under the Disease Progression Curve (ABCPE). At the highest dose of AE (≈ CE90), the ABCPE was reduced to 6.9 ± 1.1 cm²·d for Fusarium sp. and 5.2 ± 1.0 cm²·d for Colletotrichum sp.—values statistically indistinguishable from the reference synthetic fungicide. The integrated approach—which links the chemical identity of EO to nonlinear inhibitory concentrations in vitro and to disease progression metrics in vivo—provides a methodologically rigorous framework for evaluating plant-based biofungicides in tropical postharvest systems.