Submitted to: Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/1999
Publication Date: N/A
Interpretive Summary: Spray applications of a naturally occurring plant chemical to young developing grapefruit were examined for effect on juice quality. The chemical is known for its growth-promoting effects on plant tissues and is used commercially in grapefruit crops, though it is usually applied much later than is done in these experiments. Various levels of the chemical were applied to grapefruit trees right after fruit set in May. They were applied two to four times; the fruit was then allowed to mature on the tree. Harvested fruit were evaluated for size and juice quality. The soluble solids (sugars), acid content, and the level of bitter-tasting compounds were determined. Treated fruit were generally larger in size and the juice had less of the bitter- tasting compound than untreated fruit, while the sugar content and acid content were unaffected. This may be an effective method to lower the levels of one of the bitter components in grapefruit juice. This research benefits both the grower and consumer of grapefruits. By reducing the level of bitterness in grapefruit juices, it should make the fruit more desirable to the consumer, thereby increasing sales.
Technical Abstract: Early spray treatments containing gibberellic acid (GA3) significantly lowers the concentration of the bitter flavonoid in fruit tissues. Sprays containing a surfactant and different levels of GA3 (5, 50, 100, and 500 ppm) or abscisic acid (ABA) (5, 25, and 50 ppm) were applied to young, developing fruit on mature grapefruit (Citrus paradisi) trees during the period from April to June, beginning just after fruit set. The fruit were allowed to mature and were harvested early the following year. Harvested fruit were evaluated for weight, juice characteristics, and flavonoid concentrations. GA3 application resulted in larger mature fruit, which yielded juice with the same soluble solids value as juice from control fruit, but with slightly lower acid percentages and lower concentrations of naringin. ABA treatment had little effect on juice soluble solids, acid content, and naringin content except at the highest concentration of 50 ppm, which lowered naringin levels slightly in juice.