citrus greening

HLB Slowed by Biocontrol

Ernie NeffHLB Management

A tree infected with HLB has small lopsided fruit.
(Photo by UF/IFAS)

Florida citrus growers may have a new tool to help them slow the presence of HLB in already diseased trees, courtesy of researchers at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS). The researchers found that injecting a benign Xylella fastidiosa EB92-1 bacteria biocontrol into infected citrus trees over a period of six years reduced the incidence of trees with severe HLB symptoms.

The discovery may provide growers with a strategy to keep trees alive and productive longer even when infected with the HLB bacterium.

Donald Hopkins, an emeritus professor of plant pathology at the UF/IFAS Mid-Florida Research and Education Center, conducted three trials in central and eastern Florida. The trials took place in commercial groves of Valencia orange and Rios grapefruit at different tree maturity stages. All of the trees tested positive for HLB at the beginning of the trial but had varying ranges of symptoms from asymptomatic, to mild to severe. The trials included young (2-year-old) and mature (greater than 20-year-old) trees.

“Using EB92-1 provided a level of control of HLB in two mature citrus tree trials and in a trial initiated in young 2-year-old trees,” said Hopkins. “This biocontrol strain has the potential to prevent or delay severe symptoms of HLB and prevent the loss of production both in mature and young citrus trees.”

All trees in the trials remained positive for HLB throughout the six-year trial. The injections of EB92-1 did not prevent or reverse infection of HLB.  But key findings indicated that trees that were treated had less increase in symptoms than untreated trees. Injected trees also had increased yield compared to untreated trees. In mature trees, results from the trials indicated that the most effective control of HLB may require once-a-year treatment for at least the first two to three years. Retreatment may be required yearly for best biocontrol.

Using EB92-1, especially when combined with fertilizer and pesticide best management practices, could prolong the life and productivity of citrus trees. Hopkins believes the positive impact comes from induced resistance. Induced resistance occurs when a plant’s resistance mechanism is activated by infecting a plant with a pathogen, such as the benign strain EB92-1.

This research was published online in April in Plant Disease, the journal of the American Phytopathological Society. The project was partially funded by the U.S. Department of Agriculture HLB Multi-Agency Coordination group and UF/IFAS. The treatment is patented and licensed to an external company and is not currently available to growers.

Source: University of Florida Institute of Food and Agricultural Sciences

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