Hairy Approach May Get to the Root of HLB

Josh McGillHLB Management, Research, Texas

Developing disease-resistant, high-quality improved crop varieties may seem like a “hairy” task, but Texas A&M AgriLife Research scientists may have gotten to the root of the issue.

Assay plate of hairy roots that may be used to develop improved varieties of citrus and other plants (Photo courtesy of Texas A&M AgriLife)

A new biological technology that develops and multiplies disease-resistant citrus plants is under development by an AgriLife Research team led by Kranthi Mandadi. Mandadi is an associate professor at the Texas A&M AgriLife Research and Extension Center at Weslaco. He is a faculty member of the Department of Plant Pathology and Microbiology and the Institute for Advancing Health Through Agriculture in Bryan-College Station.

The project is developing new ways to fight fastidious pathogens that infect plants and resist growth in a lab setting for study. One such fastidious pathogen causes HLB.

Since 2021, Mandadi has spearheaded a $7 million U.S. Department of Agriculture National Institute of Food and Agriculture (NIFA) multi-state coordinated agricultural project that is also a designated NIFA Center of Excellence to combat HLB.

In recent years, Mandadi and his team developed a breakthrough method as an alternative means to propagate fastidious bacteria responsible for HLB and other insect-vectored diseases. “We developed a technology that uses pathogen-infected host tissues to produce so-called ‘hairy roots’ that can serve as biological vessels for the propagation of these pathogens in the laboratory,” Mandadi said.

The hairy root screening technique has led to the discovery of new antimicrobial peptides and chemicals with proven efficacy in plant materials, said Sonia Irigoyen, an AgriLife Research scientist who helped develop the hairy root technology. She said these antimicrobials could be used as therapies to control HLB and other plant diseases.

In their most recent study, team members investigated how to use this hairy root technique in plant transformation and bioengineering improved citrus. In the study published in the Plant Biotechnology Journal, team members showed proof of the concept of engineering citrus using hairy roots. In addition to Mandadi and Irigoyen, study co-authors include Manikandan Ramasamy, Michelle Dominguez and Carmen Padilla, all AgriLife Research scientists at Weslaco. The study was supported by grants from the U.S. Department of Agriculture, the Foundation for Food and Agricultural Research, Texas A&M AgriLife Research Insect-Vectored Disease Seed Grants and the Institute for Advancing Health Through Agriculture.

“Developing new plant varieties with improved genetics using conventional breeding or the latest bioengineering and CRISPR tools can be quite laborious, often taking multiple years,” Mandadi said. “The ability to overcome this bottleneck and improve this process, particularly for hardy, slow-growing, perennial trees like citrus, can be a game changer.”

Ramasamy said the efficiency of genetic modification of tree crops like citrus has been challenging due to their slow growth and difficulties in regeneration. “However, we were able to demonstrate a versatile R. rhizogenes-mediated hairy root induction, plant regeneration and clonal propagation approach that could be helpful for multiple bioengineering and gene-editing applications in citrus and other tree crops,” he said.

The proposed R. rhizogenes-mediated citrus hairy root induction, shoot regeneration and multiplication process achieved in about six months what typically took approximately 12 to 18 months. “The entire throughput for developing more disease-resistant citrus and other plants will be greatly expedited” as a result of the research, Mandadi said.

He added that the hairy-root mediated transformation could speed the development of new varieties with superior disease resistance, resilience to environmental stresses, increased production efficiency and improved nutritional quality.

Source: Texas A&M AgriLife Research

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