Low relative humidity at harvest and before storage at high humidity influence the severity of postharvest peel pitting in citrus

Several citrus cultivars including 'Marsh' grapefruit (Citrus paradisi Macf.) and 'Fallglo' tangerine [Bower citrus hybrid (C. reticulata Blanco x C. reticulata x C. paradisi) x Temple tangor (C. reticulata x C. sinensis L. Osbeck)] are prone to develop postharvest peel pitting at nonchilling temperatures. This disorder is characterized by depressions in flavedo that ultimately affect oil glands. Although the fundamental cause for this disorder has not been well defined, increasing evidence indicates that alteration in peel water status during postharvest handling of fruit plays a major role. 'Fallglo' tangerines developed postharvest peel pitting when transferred from low (30%) to high (90%) relative humidity (RH) storage. To determine the number of hours of dehydration prior to storage at high RH sufficient to induce peel pitting in 'Marsh' grapefruit and 'Fallglo' tangerines, fruit were exposed to low RH conditions for increasing periods of time and then washed, coated with commercial shellac-based wax, and stored at high RH. Only 2 hours of low RH storage were sufficient to induce peel pitting in 'Fallglo' and 'Marsh' after transfer to high RH. The severity of pitting in 'Fallglo' tangerines was greater than in 'Marsh' grapefruit. Weight loss of fruit at the end of low RH storage and peel pitting after 3 weeks of storage at high RH were significantly correlated. RH conditions in the field at the time of harvest affected susceptibility to peel pitting in both cultivars. Peel pitting was more severe when fruit were harvested at low field RH than high field RH when followed by treatments that induce peel pitting. The data suggest that harvesting susceptible cultivars at high RH, and minimizing exposure to low RH after harvest, could reduce the commercial impact of postharvest peel pitting.