Brassinosteroids Help Trees After IPC Removal

Associate Professor Fernando Alferez and his team at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) learned several years ago that individual protective covers (IPCs) protect newly planted trees from HLB. They do that by excluding the Asian citrus psyllids (ACP) that spread the devastating citrus disease.

But multi-county citrus Extension agent Mongi Zekri noted that IPCs must be removed after two or three years, leaving the trees exposed to ACP. Fortunately, Zekri said, Alferez’s team later discovered that adding a brassinosteroid (BR) treatment when IPCs are removed may prolong tree health and improve fruit yield and quality.

Zekri used that summary to introduce Alferez’s recent presentation on evaluating BRs to improve citrus fruit quality and tree protection under HLB. BRs are growth hormones found in most plants. As commercial products, they control plant growth and development. 

BR BENEFITS

Following Zekri’s introduction, Alferez reported that six months after IPCs are removed from young trees, most trees become infected with HLB. However, he reported the following positive results six months after IPC removal for trees that had BR treatments:

• More abundant, earlier and synchronized flushes
• Denser canopy and greener leaves
• More chlorophyll content
• More fruit set
• Most trees still negative for HLB
• Thicker rootstock
• Larger canopy volume
• Some new phloem vessels
• Less callose deposition
• Increase in enzymes related to oxidative stress alleviation

CONCLUSIONS

Alferez concluded his presentation with the following summary points:

• BRs improve growth, branching and immunity if applied to young trees less than 3 years old.
• Applying BRs at the right time to mature citrus trees improves internal fruit quality.
• The effect of BRs is significant in mature trees at 3 or less in the scale of HLB damage. There is a strong potential for BR use in oxytetracycline-treated trees, as these trees show signs of recovery and improved health.
• BRs may recover trees already affected by HLB if no reinfection occurs.

See Alferez’s full presentation on brassinosteroids below or here.

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