Trees’ own beneficial microbiome could lead to discovery of new treatments to fight citrus greening disease
By Kateel G. Shetty, Florida International University; Jessica Dominguez, Florida International University, and Krishnaswamy Jayachandran, Florida International University,
7 hours ago
(MIAMI) Citrus trees showing natural tolerance to citrus greening disease host bacteria that produce novel antimicrobials that can be used to fight off the disease, our recent study shows . We found the trees at an organic farm in Clermont, Florida.
Infected trees produce fewer fruit. The fruit that does grow is partially green, smaller, shaped irregularly and bitter tasting. It may drop from the trees before ripening. Leaves may show blotchy mottling.
According to the U.S. Department of Agriculture, the 2022-2023 growing season was the least productive since 1936 . Smaller crops lead to higher prices on oranges, tangerines, grapefruits, lemons and limes.
In a search for treatments against HLB, we looked to endophytes of survivor citrus trees – in other words, trees that are HLB positive but showed only mild symptoms and continue to bear fruit. By studying 342 endophytes of survivor trees, we discovered five bacterial endophytes capable of producing novel antimicrobials.
The HLB bacteria cannot be grown on laboratory culture media like agar or broth. So, we used live bacterial cells present in the ground tissue samples of infected psyllids to test the antimicrobial compounds in the lab. These studies revealed that the antimicrobial compounds were highly effective at killing the live cells of citrus greening pathogen in this controlled environment . The antimicrobials can be mixed with water and were found to be effective at low concentrations.
What’s still not known
Preliminary results from our ongoing work indicate that multiple antimicrobial compounds are present in the bacterial culture extract. This is a positive sign because the antimicrobial compounds may be found to attack pathogenic bacteria in several different ways. If that’s the case, it will help minimize the development of resistance in the same way a variety of antibiotics are useful to human doctors.
One of our next steps will be to evaluate selected compounds against HLB, using infected citrus roots under laboratory conditions and infected citrus plants under greenhouse conditions, to test whether the plants will absorb these antimicrobial compounds through their leaves or roots. This work will be conducted in collaboration with scientists from Texas A&M University and the University of Florida.
What’s next
Further research will focus on methods to increase the production of purified antimicrobial compound in order for it to be evaluated in the field. To help get the technology to growers faster, we may look for partnerships with interested commercial biopesticide companies to help with product development.
Our work has taken on new urgency due to emerging psyllid-transmitted diseases that infect potato, tomato and carrot crops in the U.S. that are caused by closely related bacterial pathogens.
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Kateel G. Shetty receives funding from USDA-NIFA Emergency Citrus Disease Research & Extension (ECDRE) program, grant number 2022-70029-38526
Jessica Dominguez received funding from USDA-NIFA-HSI Higher Education Grants Program (2016-38422-25549), USDA-NIFA-NNF (2021-38420-34074), USDA-NIFA-ECDRE program (2022-70029-38526), and financial support of FIU Doctoral Evidence Acquisition Fellowship to help fund her master’s and dissertation research at Florida International University.
Krishnaswamy Jayachandran receives funding from several USDA-NIFA programs - Hispanic Serving Institutions, National Needs Fellowship, Research Experience & Extension for Undergraduates, Beginning Farmers & Ranchers Development Program.
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