While it remains to be seen if trunk injection of oxytetracycline hydrochloride (OTC-HCl) is a game changer in the fight against HLB, it certainly has intensified the conversation about the potential for antimicrobial treatments.
There are literally hundreds of materials that might be effective at reducing the HLB bacteria in trees, but it has been a slow process to screen these materials. Kranthi Mandadi, an associate professor of plant pathology and microbiology with Texas A&M University, spoke at the recent Florida Citrus Industry Annual Conference about ways to speed up the process.
One of the big stumbling blocks has been the inability to effectively culture the HLB bacteria in the lab. Using hairy root assays grown in the lab is a workaround for this problem and allows scientists to test potential HLB treatments in a quicker fashion. The hairy roots can be grown in the lab and are infected with HLB. When a potential treatment is applied, the HLB levels can be measured to gauge the material’s ability to kill the bacteria.
“It is about four times faster than a traditional test that you would include in a greenhouse or in a field trial,” Mandadi said. “It is not going to replace those trials, but it will step up the speed of preliminary screening. You can add many different antimicrobials (treatments) to the plate with the hairy roots.”
This process has allowed Mandadi and his team to evaluate many microbial and peptide materials. They have been working with various collaborators, including Bayer, to evaluate potential HLB-therapy candidates.
Three especially promising antimicrobials have been identified that are being moved into further testing in the greenhouse and field. Researchers will be studying how the materials work alone and in combination with OTC-HCl.
Mandadi also has been evaluating a class of peptides called defensins. These are naturally occurring proteins in plants. A defensin from spinach performed very well in the hairy root assay testing to reduce the HLB bacteria. It is being developed and tested in collaboration with the University of Florida and Southern Gardens Citrus. The method uses a technique to introduce the peptide into the tree via a virus vector rather than trunk injection. Southern Gardens Citrus is currently seeking collaborators to take the product through the regulatory process into commercialization.
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