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Short Exposure to High CO₂ and O₂ at Curing Temperature to Control Postharvest Diseases of Citrus Fruit

Curing of citrus fruit at 30 to 37°C and 90 to 98% relative humidity for 65 to 72 h is an effective alternative to fungicides to control postharvest green and blue molds caused by Penicillium digitatum and P. italicum, respectively. However, commercial adoption is limited because treatment is long and it may harm fruit quality. In order to improve the feasibility of curing, short CO₂ or O₂ exposures at curing temperature were evaluated on ‘Nadorcott’, ‘Clemenules’, and ‘Ortanique’ mandarin fruit and ‘Valencia’ orange. Fruit were artificially inoculated, exposed 24 h later to air (control); CO₂ at 15, 30, 50, or 95 kPa; or O₂ at 30 or 45 kPa at 20 or 33°C for 8, 24, or 48 h and incubated at 20°C for 4, 7, or 15 days. Exposure at 33°C with CO₂ at 15 kPa for 24 h or O₂ at 30 kPa for 48 h effectively controlled both green and blue molds after 7 days of incubation at 20°C; however, control of both diseases was minimal after 15 days. To assess potential induction of disease resistance, fruit were treated as described above, then inoculated after 1, 2, or 5 days at 20°C and evaluated after 3 and 6 more days at 20°C. All of the treatments were ineffective in inducing fruit resistance. Short exposures of citrus fruit to high CO₂ or O₂ at curing temperatures may be part of a control program alternative to synthetic fungicides, especially for organic fruit markets.