By Fernando Alferez and Divya Aryal
Brassinosteroids (BRs) are a class of plant growth regulators with several effects on plant growth and development. University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) work in the last few years has shown that BR treatments may influence internal maturity in Hamlin sweet orange if performed at the right time. Research has determined that a treatment of 186 milliliters of BR (0.1%) per 100 gallons of water applied just once at the right time of fruit maturation has the most consistent results.
For mature trees 7 years or older, 1 gallon of the prepared solution per tree is typically used for full tree coverage. In Hamlin, significant differences in Brix were seen when treatments are performed in a time window between mid-November and mid-December, with harvesting occurring two weeks after treatment. In these conditions, an increase in Brix from 7.9 (controls) to 8.9 (BR-treated trees) was realized.
Results may vary depending on tree health status. Trees in better shape respond better to the treatments. Using a tree health scale from 0 (healthy looking trees with a dense canopy) to 5 (abundant limb dieback, scarce canopy with small leaves and blotchy mottle symptoms), there were better consistent results in trees ranking at 2 or 3. (Trees ranking at 0 or 1 were not available.) A score of 2 or 3 is consistent with trees that are still retaining a dense canopy and show no twig dieback.
The graph shows results when Brix is pooled as a function of tree health status. By doing this, the differences are even more pronounced, with BR-treated trees at a score of 2 to 3 showing Brix at 9.5 as compared to BR-treated trees that were at a score of 4 (declining trees) showing no differences with non-treated controls (Brix around 8.4).
Research is now investigating the use of BRs in trees that have recovered a dense healthy canopy after oxytetracycline treatment. It is hypothesized that the better health status will result in a better response to the BR sprays and better fruit quality.
Acknowledgement: This research is supported with funding from the Citrus Research and Development Foundation (grants 22-003 and 24-001).
Fernando Alferez is an associate professor, and Divya Aryal is a graduate Ph.D. student — both at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
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