Granulation in Florida Citrus

Granulation (also called crystallization or section drying) is a physiological disorder in citrus that results in reduced extractable juice and sometimes vesicle shriveling. While segments appear dry, the disorder is not caused by drying, but by gel formation within the vesicles. Though many citrus varieties may develop granulation (i.e., ‘Valencia’ orange, tangerines, and grapefruit), it was a particular problem in Florida ‘Navel’ oranges during the 2003 season. Many factors have been associated with the development of granulation in citrus, including advanced fruit maturity, large fruit, excessive tree vigor, severe mite damage, composition of the juice, and cool, dry, windy weather conditions. Tree water status and irrigation have also been reported to affect granulation with researchers reporting less granulation with less irrigation. During the 2003 navel orange season, the relatively high temperatures during bloom, low fruit set, and associated larger fruit likely played an important role in the excessive development of granulation in the fruit. Changing cultural practices (i.e., fertilization and irrigation) and use of rootstocks that encourage vigorous tree growth may have promoted the development of granulation, but specific data and their related impact on granulation in Florida are limited. What is Granulation? Granulation (also called crystallization or section drying) is a physiological disorder in citrus that results in reduced extractable juice and sometimes vesicle shriveling (Fig. 1). While segments appear dry, the disorder is not caused by drying, but by gel formation within the vesicles (Bartholomew et al., 1941). Freezing and sunburn cause injury that can be mistaken for granulation, but these events cause cellular colThis research was supported by the Florida Agricultural Experiment Station, and approved for publication as Journal Series No. N-02583. Trade and company names are included for benefit of reader and imply no endorsement or preferential treatment of products by the University of Florida. 1 Corresponding author. Fig. 1. Granulation of navel orange.