Postharvest Peel Pitting in Citrus Fruit at Nonchilling Temperatures Is Affected by Climatic Factors and Advanced by Changes in Peel Water Status

Abstract

Several citrus varieties, including `Navel' oranges, `Marsh' grapefruit and `Fallglo' tangerines are prone to develop postharvest peel pitting at nonchilling temperatures. The disorder is characterized by depressions in flavedo that ultimately affect oil glands. Increasing evidence indicates that changes in peel water status during postharvest handling of fruit plays a major role in the appearance of the disorder. Peel pitting was triggered when fruit were transferred from low to high relative humidity (RH) consistently in several citrus growing areas. A transient increase in fruit ethylene production and ABA content was observed within the first 24 hours after transfer from low to high RH. Water potential decreased with storage at low RH in flavedo and albedo, and recovered faster in flavedo than in albedo cells upon transfer to high RH. The differential recovery in water potential between flavedo and albedo is postulated to cause collapse of external albedo layers and pitting. The effect of climatic conditions in the field at harvest was also examined. Harvesting fruit at low RH induced more severe pitting after storage than harvesting at high RH. In addition, increasing hours of low RH storage prior to storage at high RH resulted in increased pitting. The results demonstrate that change in peel water status is a major factor leading to the development of postharvest peel pitting in citrus.