Mechanisms of rind-oil spot development in 'Encore' (Citrus nobilis Lour. x C. deliciosa Ten.) fruit

Abstract

Causes of the rind-oil spot disorder that occur on the rind surface of 'Encore' fruit were examined from physiological and ecological aspects. The occurrence seems to be closely associated with physiological stages of rind tissues; the spots develop in fruit larger than 4 cm in diameter from late August to early November. Furthermore, the disorder occurred only in the fruit derived from the flowers which bloomes in April but not in those from the July bloom. A more severe disorder was found in the fruit born in the exterior of a canopy than in those of the interior, as well as on the sun-lit rather than on the shaded sides of the same fruit. The surface exposed to direct radiation exceedes 38 °C. The affected tissue collapsed, became dehydrated, and developed green pits which gradually turned into yellow or brown. The essential oils that leaked from the oil glands of the affected parts caused them to enlarge. An application of the essential oils extracted from the peel of 'Encore' fruit induced similar rind-oil spots on healthy fruit.