In vitro activity of eighteen essential oils and some major components against common postharvest fungal pathogens of fruit |
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| Authors: | S CombrinckT Regnier GPP Kamatou |
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| Institution: | a Department of Chemistry, Tshwane University of Technology, PO Box 56208, Arcadia 0007, South Africa
b Department of Pharmaceutical Sciences, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa |
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| Abstract: | The development of natural crop protective products as alternatives to synthetic fungicides is currently in the spotlight. In vitro experiments are valuable precursors to more costly in vivo trials, allowing the identification of effective essential oils and establishing the concentrations required for inhibition of a specific, or spectrum of decay pathogens. In this study, the antifungal properties of eighteen essential oils were evaluated in vitro by addition to the fungal growth medium of five pathogens (Lasiodiplodia theobromae, Colletotrichum gloeosporioides, Alternaria citrii, Botrytis cinerea and Penicillium digitatum) isolated from mango, avocado, citrus, grapes and cactus pear. The inhibitory properties of some of the major compounds of the oils, identified and quantified by gas chromatography-mass spectroscopy and gas chromatography-flame ionization detection were also determined. Most of the oils were selected on the basis of commercial availability and for containing a predominant compound. Visual inspection of fungal growth was done and the lowest concentration where fungal growth was completely inhibited on all replicates was recorded. Thyme oil proved to be the most effective inhibitor, totally inhibiting all of the pathogens tested at concentrations of 1000 μl/l and lower, with the exception of a resistant Penicillium strain. Cinnamon oil, rich in eugenol (81.2%), demonstrated good fungicide potential, while the carvone-rich oils displayed promising activity against the citrus pathogens. Oils characterized by high concentrations of S-carvone were less effective than those containing the R-enantiomer. Essential oil of Lippia citriodora was active against all of the pathogens, excluding L. theobromae from avocado. These essential oils, applied alone or in combination, are good candidates for further in vivo testing and for investigations concerning their modes of action. |
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| Keywords: | Alternaria spp Botrytis cinerea Colletotrichum gloeosporioides Lasiodiplodia theobromae Penicillium spp Essential oils Fruit Postharvest pathogens |
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