|SINGH, SUKHDEEP - University Of Florida|
|LIVINGSTON, TAYLOR - University Of Florida|
|VASHISTH, TRIPTI - University Of Florida|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2021
Publication Date: 1/25/2022
Citation: Singh, S., Livingston, T., Tang, L., Vashisth, T. 2022. Effects of exogenous gibberellic acid in huanglongbing-affected sweet orange trees under Florida conditions - II. fruit production and tree health. HortScience. 57(3):353-359. https://doi.org/10.21273/HORTSCI16277-21.
Interpretive Summary: Florida citrus production has been decreasing since the outbreak of Huanglongbing (HLB) disease a decade ago. In this study, the effects of gibberellic acid on fruit development and tree health were evaluated in citrus trees affected by HLB. Compared to non-treated control, gibberellic acid applications increased fruit size, fruit retention and yield, and prevented additional branch loss caused by the disease. These results suggest, since there is no cure for HLB currently, gibberellic acid may be used to improve citrus fruit production and maintain tree health in the presence of HLB.
Technical Abstract: Fruit production of sweet orange (Citrus sinensis) in Florida have been declining with the presence of Huanglongbing [HLB Candidatus Liberibacter asiaticus (CLas)] disease. Through disrupting the balance of endogenous hormone levels, the disease has negative impacts on fruit development, mature fruit retention, and overall tree health. Thus, the goal of this research was to determine whether plant growth regulator gibberellic acid (GA3) can be used to improve the production issues caused by HLB. For ‘Valencia’ sweet orange, although foliar applied GA3 from September to January (33 mgL-1 for 5 applications) resulted in 50% decrease in bloom the following spring, this treatment did not cause reduction in yield of current and subsequent crops. The size of mature fruit was also increased (by 4-5%) with reduced fruit drop rate near harvest in GA3-treated trees compared to non-treated control trees. Furthermore, the canopy density, an indicator of HLB severity, was maintained in trees applied with GA3 for four consecutive years (from 90.8% light interception in year 1 to 90.4% in year 4). In contract, there was a substantial decrease in canopy density for control trees (from 91.6% to 84.0%). Given that there is no cure for HLB, these results presented a possible remedy of using GA3 in sustaining tree health for field-grown sweet orange affected by HLB.