Gibberellic Acid, Rootstocks, and Post-freeze Fruit Quality of 'Rohde Red' Valencia Oranges

The authors' objectives were to determine whether gibberellic acid (GA3) initially increases juice content of 'Rohde Red' valencia oranges and prevents or delays decreases in juice content after a freeze, and to determine whether there is an interaction between GA3, rootstock, and juice content. The experiment consisted of a 2 (+, -GA3) x 3 (rootstock) factorial using a completely randomized design with 10 replications per treatment. Gibberellic acid was applied to mature 'Rohde Red' valencia Citrus sinensis (L.) Osb. orange trees on three rootstocks-Citrus volkameriana Ten. & Pasq.(Volk), Swingle citumelo C. paradisi Macf. xPoncirus trifoliata (L.) Raf., and Carrizo citrange C. sinensis xP. trifoliata-at color break in Fall 2002, 2003, and 2004. Juice content, soluble solids content (SSC), titratable acidity (TA), ratio of SSC to TA, and kilogram solids per box were determined at about 2-week intervals after several freezes. In 2002-03 and 2004-05, juice content in the fall was greater and the rate of decrease in juice content lower for GA3-treated fruit than nontreated fruit for about 8 weeks after a freeze. In contrast, in 2003-04, juice content and rate of decrease in juice content were not different between treatments. Juice content was lower for fruit from 'Rohde Red' trees on Volk compared with those on Carrizo and Swingle, and more important, the rate of decrease in juice content after a freeze was greatest for trees on Volk in all three seasons. Soluble solids content, TA, SSC-to-TA ratio, and kilogram solids generally were not effected by GA3 treatment. Therefore, GA3 application at color break in the fall generally increased juice content and slowed the rate of decrease in juice content after a freeze compared with nontreated fruit. In addition, juice content differed significantly with rootstock, but there was no GA3 x rootstock interaction.