The potential use of antifungal essential oil volatiles to manage citrus decay during degreening

New developing regulations of chemical-use on fruit calls for an integrated disease management approach using softer chemicals to reduce decay of fresh produce. The aim of this study was to evaluate the potential use of essential oil volatiles to manage postharvest citrus decay. Fifteen essential oils were tested in vitro for its fungicidal properties against growth- and spore-germination of two postharvest citrus pathogens. Cinnamon bark and oregano oils were fungicidal to fresh mycelial-growth of Penicillium digitatum (cinnamon: ≥ 212; oregano: ≥ 106 µl/L headspace) and Galactomyces citri-aurantii (cinnamon: ≥ 106; oregano: ≥ 212 µl/L headspace). Oregano inhibited sporulation of P. digitatum (≥ 53 µl/L headspace). When spores of these pathogens were exposed to cinnamon bark essential oil (≥ 106 µl/L headspace) for 72 h, spore germination was inhibited by 100% (P. digitatum) and 99% (G. citri-aurantii). Combining cinnamon with oregano (both at 53 µl/L headspace) inhibited spore germination, whilst inhibiting the sporulation of P. digitatum. Cinnamon (168 µl/L headspace) and oregano (84 µl/L headspace) tested in the absence of growth media were fungicidal to 100% of P. digitatum spores after 24 h exposure. Cinnamon (133 µl/L headspace) reduced green mould (43% control) when tested on sterile-wounded ‘Valencia’ oranges in the presence of a fruit sporulating with P. digitatum. Oregano (106 µl/L headspace) inhibited the sporulation on fruit injected with P. digitatum. These essential oils did not significantly affect degreening of ‘Eureka’ lemons when treated together with ethylene. This study demonstrates the potential use of cinnamon bark and oregano actives to manage postharvest decay of citrus during degreening.