Spinach Peptides Provide Defense Against HLB

Texas A&M AgriLife Research scientists have developed an approach to countering the citrus disease HLB as well as zebra chip disease in potatoes and other vegetables. Their method uses spinach antimicrobial peptides, known as defensins, which naturally defend plants against a broad range of pathogens. Their study results were recently published in the Plant Biotechnology Journal. The effects show significant progress toward recovering yield and improving quality in diseased plants.

Kranthi Mandadi, a plant molecular biologist and professor in the Texas A&M Department of Plant Pathology and Microbiology, led the study. Mandadi works at the Texas A&M AgriLife Research and Extension Center at Weslaco.

Collaborators in the study include Texas A&M researchers Carmen Padilla, Sonia Irigoyen, Manikandan Ramasamy, Mona Damaj, Michelle Dominguez, Denise Rossi and Renesh Bedre; University of Florida Institute of Food and Agricultural Sciences researchers William Dawson and Choaa El-Mohtar; and Michael Irey at Southern Gardens Citrus.

Mandadi and his team chose spinach antimicrobial peptides after learning from previous studies that they can fend off various pathogenic fungi and bacteria. Because these peptides occur naturally in spinach, they’re also frequently consumed by humans. In 2021, the U.S Environmental Protection Agency concluded that dietary exposure to spinach defensins is safe for the U.S. population, including infants and children. This makes them an attractive choice for both effectiveness and safety, as they pose no known health risks.

The researchers delivered the peptides to commercial citrus trees using a benign virus developed by University of Florida researchers, who collaborated on the study. The virus naturally infects the trees in the same location where the disease-causing bacteria reside. Using a simple grafting procedure, the researchers were able to apply the virus and allow it to deliver the peptides targeting the bacteria largely on its own.

Over a few years, the research team monitored how citrus trees infected with Candidatus Liberibacter asiaticus, the bacterium responsible for HLB, responded to treatment with specific antimicrobial peptides. They saw promising results, including up to 50% increases in fruit yield compared to untreated trees after only a single application.

Southern Gardens Citrus, a subsidiary of U.S. Sugar, has licensed patent rights for the defensins technology developed by AgriLife Research from The Texas A&M University System, as well as the use of the viral vector technology from the University of Florida. They are working with Silvec Biologics to commercialize this technology for use against the bacterium responsible for HLB. Silvec filed an application with EPA in January 2024 to allow for commercial use.

The study was funded by the U.S. Department of Agriculture National Institute of Food and Agriculture, along with support from Southern Gardens Citrus and AgriLife Research funds.

Source: Texas A&M AgriLife