Tolerance of selected orange and mandarin hybrid fruit to low-dose irradiation for quarantine purposes

Tolerance of many citrus cultivars to low dose irradiation treatment is not known. Ten citrus cultivars grown in Florida, including the five orange [Citrus sinensis (L.) Osbeck] cultivars, Ambersweet, Hamlin, Navel, Pineapple, and Valencia, and the five mandarin hybrids (Citrus reticulata Blanco),'Fallglo', 'Minneola', 'Murcott', 'Sunburst', and 'Temple', were exposed to irradiation at 0, 0.15, 0.3, and 0.45 kGy, and stored for 14 days at 1 degreesC or 5 degreesC plus 3 days at 20 degreesC, to determine dose tolerance based on fruit injury. Softening of 'Valencia', 'Minneola', 'Murcott', and 'Temple' was dose-dependent, but that of other cultivars was unaffected. Only 'Ambersweet', 'Valencia', 'Minneola', and 'Murcott' did not develop peel pitting at 0.15 kGy or higher. Total soluble solids of 'Ambersweet' and 'Sunburst' declined slightly with increasing dose. Titratable acidity (TA) of oranges was not affected, but TA of 'Sunburst' and 'Temple' juice was slightly reduced by irradiation at 0.45 kGy. Juice flavor of 'Hamlin','Navel', 'Valencia', and 'Minneola', and pulp flavor of 'Hamlin', 'Valencia', 'Fallglo', 'Minneola', and 'Murcott' was less acceptable after irradiation at 0.3 or 0.45 kGy. The appearance of all cultivars was negatively affected by the loss of glossiness with the 0.45 kGy dose. Less than 1.0 % of fruit decayed and irradiation treatment had no effect on decay. Our study indicates that growers and shippers need to be aware that the effects of irradiation on citrus fruits are highly variable and both cultivar-dependent and dose-dependent.