Gibberellic Acid Inhibits Floral Bud Induction and Improves `Bing' Sweet Cherry Fruit Quality

This paper reports on the potential of gibberellic acid (GA 3 and GA 4+7 ) to reduce sweet cherry ( Prunus avium L.) floral bud induction and balance fruit number and improve fruit quality in the season following application. In 2003, GA 3 was applied to `Bing'/`Gisela 1' trees at 50 and 100 mg·L -1 at the end of stage I of fruit development, end of stage II, and on both dates. These treatments were compared to the industry standard application of 30 mg·L –1 applied at the end of stage II and an untreated control. Fruit quality was evaluated in the year of application (i.e., nontarget crop) and return bloom, fruit yield and quality were assessed in the subsequent season (2004). In 2003, GA 3 delayed fruit maturity proportional to rate. In 2004, bloom density and fruit yield were related negatively and linearly to GA 3 concentration. GA 3 reduced the number of reproductive buds per spur and did not affect the number of flowers per reproductive bud. Nonspur flowering at the base of 1-year-old shoots was more inhibited by GA 3 than flowering on spurs. Double applications significantly reduced bloom density and yield versus single applications. Trees treated with two applications of 50 and 100 mg·L –1 yielded fruit with 7% and 12% higher soluble solids, 15% and 20% higher firmness, and 7% and 14% greater weight, respectively. However, no treatment improved crop value per tree. In a separate isomer trial, GA 3 and GA 4+7 were applied to `Bing'/`Gisela 1' trees at 100 and 200 mg·L –1 at both the end of stage I and II in 2004. GA 3 and GA 4+7 applied at 100 mg·L –1 reduced bloom density similarly by 65%. GA 3 was more inhibiting than GA 4+7 at 200 mg·L –1 , reducing bloom density by 92% versus 68%. We observed a 4- to 5-day delay in flowering from both GA formulations at 200 mg·L –1 . At both concentrations, GA 3 reduced yield by 71% and 95% versus 34% and 37% reduction by GA 4+7 . Fruit weight and soluble solids were unaffected but fruit firmness was increased by all treatments (6% to 17%). However, crop value per tree was highest from untreated control because improvements in fruit quality were insufficient to offset reductions in yield. GA 3 shows potential as a novel crop load management tool in productive `Bing' sweet cherry orchard systems.