The Influence of Gibberellic Acid (GA) on Postharvest Pitting of Citrus

Abstract

Postharvest pitting is a citrus peel disorder that is characterized by the physiological breakdown of oil glands and is caused by high temperature storage waxed fruit. Pitting can be controlled by low temperature storage (>10 °C) or application of waxes with high gas permeability. However, refrigeration is costly and often difficult to implement while waxes with higher gas permeabilities have gloss values that are considered to be insufficient for consumer acceptance. Consequently, packers would like to control or predict pitting incidence prior to postharvest stress. Pitting incidence within a grove can vary dramatically within a season despite comparable postharvest handling. Thus, peel susceptibility may be not only variable, but alterable. Peel physiology is readily altered by early-season application of GA, a method currently used to retard peel maturation. Since the influence of GA on postharvest pitting is not known, we examined the effect of early-season foliar-applications of GA on peel quality of `Fallglo' tangerines and white grapefruit. Fruit were harvested throughout the season, washed, coated with shellac-based wax, and stored at 21 °C and 93% RH. GA applied with a silicone surfactant retarded peel maturation as indicated by greener, firmer peels. Pitting incidence was typically less for GA-treated fruit during the initial days of storage. However, GA suppression of pitting did not always persist throughout storage. GA did not affect internal levels of O2, CO2, ethanol, or acetaldehyde or weight loss. While the effectiveness of GA was not consistent, the results suggest that GA application strategies could be developed to suppress pitting. Also, GA treatments may help define factors that determine fruit susceptibility to postharvest pitting.