5 New Research Projects Take a Swing at Solving Citrus Greening
October 25, 2023 The fight against citrus greening (aka, HLB) rages on. Despite nearly two decades of attrition to the malady, hope still grows. University of Florida scientists, which have been in the thick of the fight from the beginning, are set to raise their efforts to control citrus greening with about $5 million in new grants from USDA’s National Institute of Food and Agriculture (NIFA).
NIFA has split funding into five grants. The grants aim to accomplish several goals, including gene editing to develop HLB-resistant citrus varieties and integrated pest management (IPM) to help keep psyllids away from citrus trees, according to UF/IFAS.
Here is a breakdown of each project.
Genome editing for better tolerance to citrus greening ($1,042,257); Principal Investigator: Nian Wang, UF/IFAS Professor of Microbiology
Researchers plan to use cutting-edge precision genome-editing technology to help plant breeders develop more varieties that are tolerant and/or resistant to citrus greening disease.
The central hypothesis for this research is that HLB can be controlled by mitigating reactive oxygen species (ROS). ROS, such as hydrogen peroxide, are chemicals that cause damage to citrus plants. Scientists plan to prevent ROS damage caused by HLB disease by increasing the levels of antioxidant enzymes in citrus plants, which in turn will reduce ROS damage.
“Transgene-free HLB-resistant/tolerant citrus varieties with suitable horticultural traits has the potential to provide the most effective, environmentally friendly and economic approach for HLB control,” Wang says.
IPM approach that delivers economic viability to citrus production with HLB ($1,128,392); Principal Investigator: Lukasz Stelinski, UF/IFAS Professor of Entomology
The long-term goal of this project is to render HLB functionally irrelevant by developing an IPM system that yields economic return from citrus. The research will address three aspects of HLB:
- Suppress psyllids to the point where management decisions are based on vector density and seasonal biological events. This way, management costs do not exceed yield losses.
- Evaluate the viability of trunk injections as a therapy to reduce bacterial populations.
- Integrate the use of gibberellic acid to mitigate disease symptoms.
“The most effective and economical combination of vector, pathogen and disease symptom management treatments will be implemented on a farm-scale level with growers in Florida and Texas,” Stelinski says.
Enhancing the delivery of therapeutics into citrus phloem by linking sugar molecules ($974,182); Principal Investigator: Amit Levy, UF/IFAS Assistant Professor of Plant Pathology
While tree-trunk injections reduce Candidatus Liberibacter asiaticus (CLas), they do not specifically target the phloem, the part of the vascular system in a citrus tree through which HLB travels. Most of the injected antibiotic is introduced in the xylem, where there’s no bacteria. Thus, the antibiotics don’t efficiently reach the phloem. Researchers will add a glucose molecule to antimicrobial compounds. This should dramatically improve their delivery into the phloem and reduce the dose needed for efficient HLB control.
Rapid generation and evaluation of eremocitrus-derived populations for HLB tolerance and fruit quality ($928,000); Principal Investigator: José Chaparro
Scientists have found HLB resistance in the citrus-related species known as Eremocitrus glauca (Australian desert lime). But transferring the resistance into commercial varieties typically takes decades because citrus remains in its juvenile stage so long. UF/IFAS has found an Eremocitrus variety with early flowering. Scientists propose to breed varieties of commercial quality with HLB-resistance, by speeding up the breeding process using early flowering varieties.
Multiomic dissection of HLB tolerance in B9-65 Valencia, N13-32 Hamlin, OLL-8 sweet orange and other cultivars ($1,364,478); Principal Investigator: John Chater
In this project, scientists will study scions with demonstrated HLB tolerance and the potential to produce commercial-grade fruit, despite testing positive for CLas. Researchers will examine plants infected in established groves and uninfected in facilities known as Citrus Under Protective Screens (CUPS). From there, they’ll make a comparative genetic and horticultural analysis of uninfected material vs. tolerant and susceptible-to-infection material. Ultimately, researchers want to distribute HLB-tolerant scions to stakeholders and to understand the biological mechanisms behind HLB tolerance for breeding HLB-tolerant and -resistant scions and for gene editing purposes.
“These five funded projects illustrate the breadth and depth of our world-class citrus research program,” says Robert Gilbert, UF Interim Senior VP for agriculture and natural resources, Dean for UF/IFAS Research, and Director of the Florida Agricultural Experiment Station. “We need every tool in our toolbox to combat HLB in an integrated manner, and this USDA-NIFA funding will be extremely helpful to UF/IFAS and our stakeholders.”
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