Bioactivity of essential oils in the control of Alternaria alternata in dragon fruit (Hylocereus undatus Haw.)

This study isolated and identified the fungus that causes postharvest disease in dragon fruit (Hylocereus undatus Haw.). The in vitro and in vivo antifungal activity of some essential oils were evaluated against the fungus. Morphophysiological and molecular identification confirmed the fungus was Alternaria alternata. The essential oils of Cinnamomum zeylanicum, Cymbopogon flexuosus, Eucalyptus globulus, Eugenia caryophyllus, and Rosmarinus officinalis were evaluated by the microdilution broth technique, disc diffusion, scanning electron microscopy, and fluorescence microscopy. Evaluation of the composition of the essential oils by gas chromatography/mass spectrometry revealed substantial amounts of eugenol as a major constituent of E. caryophyllus and C. zeylanicum (90.50% and 80.70%, respectively). The other essential oils of R. officinalis contained α-pinene (24.5%) and camphor (22.0%) as major components. E. globulus contained 1,8-cineole (78.9%). C. flexuosus contained neral (35.1%) and geranial (42.6%). C. zeylanicum and E. caryophyllus were the most active against the isolated fungi at minimum inhibitory concentrations of 250 and 500 μg/ml, respectively, causing morphological changes in the hyphae. The in vivo assay indicated that the fruits that were treated with E. caryophyllus at concentrations of 500 and 1000 μg/ml exhibited a 31% reduction of mycelial growth compared with the control. These results suggest that the essential oils of C. zeylanicum and E. caryophyllus are active against A. alternata both in vitro and in vivo, which may be promising for control of the microorganism.