December 1, 1997
- plant growth regulators
The plant growth regulator, gibberellic acid (GA[sub3]), is used routinely in several citrus producing countries to delay peel senescence of fruit for the fresh market, thereby improving on-tree storage and postharvest life. In this study, GA[sub3] (ProGibb®), or GA[sub3] + 2,4-D or AVG (aminoethylvinylglycine) stop drops were applied to mature 'Hamlin', 'Pineapple', and 'Valencia' orange (Citrus sinensis (L.) Osbeck) trees to determine if the delay in fruit peel senescence improved juice extraction weight during commercial processing of orange juice. GA[sub3] (18 g ai/acre) was applied before peel color break in Sept. or Oct. in 1996 using commercial airblast sprayers at 125-166 gallons/acre in two commercial groves. An organosilicone surfactant (0.05% v/v) was added to the spray mixture to increase uptake of the GA[sub3]. Fruit samples were collected monthly from Dec. to May. Fruit peel color and resistance to puncture (firmness) were measured using a colorimeter and electronic force gauge, respectively. Processing yield was analyzed on 40- pound samples by the Florida Department of Citrus using a commercial FMC extractor. Juice yield was statistically greater for all GA[sub3] treatments in Dec. for 'Hamlin' and in Apr. for 'Pineapple' and 'Valencia' oranges. Additionally, juice yield was numerically higher for the GA[sub3] vs. nonsprayed treatments at most other dates. However, there were no statistical differences in juice weight at these dates. Peel puncture resistance was greater and color development was delayed after all GA[sub3] treat- ments throughout the season in all cultivars. Juice Brix, acid, and ratio were generally not affected by GA[sub3] treatment. Applications of GA[sub3] have the potential to improve processing juice extraction weight by 3.2 to 9.4% depending on cultivar and harvest time.