Orange oil postharvest dips for control of grey mould (Botrytis cinerea) of plums and strawberries, and green mould (Penicillium digitatum) of citrus

Orange oil has antibacterial properties for uses in food and pharmaceutical industries. This study evaluated the efficacy of orange oil dip applications and treatment periods for protective and curative effects against Botrytis cinerea, (which causes grey mould on plums and strawberries), and Penicillium digitatum, responsible for green mould of citrus. Pure orange oil and two orange oil-based formulations (OR007B and OR79) were tested on inoculated fruit, at oil concentrations from 0.05% to 1.00%, and were compared to the fungicides fludioxonil at 300 mg. L-1 for B. cinerea, or imazalil at 500 µg mL-1 for P. digitatum, the respective South African registered doses for these fungicides. Orange oil treatments failed to control green mould on lemons and oranges, with disease incidence exceeding 90% even after 120 sec of exposure. Two plum cultivars had different susceptibilities to grey mould, and orange oil reduced the disease incidence (24 to 14%) as the oil concentration increased in the curative treatments of cv. African Delight, outperforming 1% fludioxonil (24%). The OR007B and OR79 formulations both gave low incidence of grey mould, with 0.5% of orange oil in these formulations resulting in up to 12% incidence (from OR007B) and 17% (from OR79). Cv. Laetitia, in contrast, had >60% incidence of grey mould across all treatments, including fludioxonil. Protective treatments showed similar trends in both cultivars. On strawberries stored at 4°C for 14 d, grey mould incidence was reduced from 82% (control treatment) to 55% (for orange oil), 21% (for OR007B), and 44% (for OR79), with the orange oil treatments having efficacy comparable to fludioxonil. These results demonstrate the potential of orange oil treatments as alternatives for grey mould management in plums and strawberries.