Texas Researchers to Lead HLB Project

Ernie Neff HLB Management, Research

A healthy grapefruit compared to one affected by citrus greening
(Photo by Texas A&M AgriLife)

Scientists from Texas A&M AgriLife Research will lead a public-private collaboration across Texas, Florida, California and Indiana to advance new, environmentally friendly and commercially viable HLB control strategies. The $7 million, four-year AgriLife Research project is part of an $11 million suite of grants from the U.S. Department of Agriculture National Institute of Food and Agriculture.

In addition to Texas A&M AgriLife, other institutions on the team include Texas A&M University-Kingsville Citrus Center, University of Florida, Southern Gardens Citrus, University of California Agriculture and Natural Resources, Purdue University and USDA Agricultural Research Service.  

“I believe this project is timely and essential,” said Dale Murden, president of Texas Citrus Mutual and Pest and Disease Management Corporation.

One major problem is getting a treatment to the infected inner parts of the tree. Treatments must reach the phloem to kill the bacteria. So, spraying treatments on leaves has little chance of success because citrus leaves’ waxy coating usually prevents the treatments from penetrating.

Second, while the bacteria thrive in phloem, they do not grow in a petri dish. Until recently, scientists wishing to test treatments could only do so in living trees, in a slow and laborious process.

Third, orange and grapefruit trees are quite susceptible to the disease-causing bacteria and do not build immunity on their own. Treatments must be tested in groves that are already infected.

The teams will be working to advance two main types of treatment, employing technologies they’ve developed in the past.

First, a few years ago, AgriLife Research lead investigator Kranthi Mandadi and his colleagues discovered a way to propagate the HLB-causing bacteria in the lab. This method involves growing the bacteria in tiny, root-like structures developed from infected trees. The team will use this so called “hairy roots” method to screen treatments much faster than would be possible in citrus trees. In these hairy roots, the team will test short chains of amino acids — peptides — that make spinach naturally resistant to HLB. After initial testing, the most promising spinach peptides will undergo testing in field trees. To get these peptides to the phloem of a tree, their gene sequences will be engineered into a special, benign citrus tristeza virus vector developed at the University of Florida.

The second type of treatment to undergo testing is synthetic or naturally occurring small molecules that may kill HLB-causing bacteria. Again, Mandadi’s team will screen the molecules in hairy roots. A multistate team will further test the efficacy of the most promising molecules by injecting them into trunks of infected trees in the field.

Southern Gardens Citrus, a collaborator on the project, is focusing on testing the peptide therapies in field trees via the citrus tristeza virus delivery system.

Another hurdle to overcome is ensuring that growers and consumers accept the products the team develops. “We have to convince producers that the use of therapies is profitable and consumers that the fruit from treated trees would be safe to eat,” Mandadi said.

Source: Texas A&M AgriLife

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