Texas A&M Builds the Nation's First Infectious Clone of Tomato Spotted Wilt Virus

For years, researchers studying tomato spotted wilt virus worked from different books. The virus mutates quickly, so no two laboratories were ever handling quite the same strain, and the disease — carried by thrips, capable of infecting more than a thousand plant species — kept finding ways around the resistance that breeders had already written into peppers and tomatoes.

A team at Texas A&M AgriLife Research has now produced a common copy. Led by Jeanmarie Verchot, a professor in the Texas A&M Department of Plant Pathology and Microbiology, the group assembled the first infectious clone of tomato spotted wilt virus, or TSWV, in the United States: a full-length DNA version of a pepper-infecting isolate that, once it enters a plant, behaves like the virus itself.

Their approach is described in "A Novel Approach to Engineering Tomato Spotted Wilt Virus Infectious Clones by Disarming Key Nodes in Anti-Viral Defenses," recently published in Molecular Plant-Microbe Interactions by the American Phytopathological Society. Verchot's graduate student Haden Ball joined the project on what began as his thesis work.

Why a clone matters to a field

TSWV is one of the more expensive viruses a vegetable grower can meet. It is transmitted by thrips, small insects that move across fields and into new growing regions on regional wind systems. Once inside a plant, the infection cuts yields and can leave a crop unmarketable, which shrinks supply and raises costs for buyers. The USDA's Risk Avoidance and Mitigation Program puts annual crop damage from the virus at roughly $100 million in Florida, Georgia, North Carolina and South Carolina alone.

Until now, growers have leaned on varieties bred to resist infection. New strains are escaping that immunity and causing widespread disease, which pushed part of the research community toward sequencing the genomes of emerging strains to understand why they hit harder. Verchot's team went the other direction and built a tool instead of a survey.

They constructed complementary DNA — a stable, storable copy of the virus's genetic material — from the full genome of a pepper-infecting isolate. That clone produces infectious virus on demand. The practical payoff is volume and speed: researchers can make unlimited quantities of the pathogen, inoculate trial plants more efficiently, and screen breeding lines far faster than a field trial calendar allows.

"This clone allows all U.S. researchers the same starting point, providing a more efficient tool for identifying the virus in crops and for creating disease management practices," Ball said.

What it changes for Texas

Texas A&M AgriLife Research vegetable breeder Kevin Crosby, a professor in the university's Department of Horticultural Sciences, is among the collaborators who will put the clone to work selecting peppers with durable resistance. Verchot said the technology is available for licensing by seed companies and biotechnology firms.

The timing lands in a busy stretch for the virus's vector. Texas A&M AgriLife Extension published new guidance on short-spined thrips, an invasive species confirmed in the Dallas area, only days ago — part of a broader effort to give growers and greenhouse operators a clearer picture of thrips pressure and the plant diseases they carry.

That second piece is where Ball expects the clone to pay off beyond breeding. Entomologists who study how thrips pick up and pass along the virus have historically been limited by how hard it is to keep standardized virus material on hand. A stable clone removes that constraint, which opens the door to research aimed at interrupting transmission rather than only treating its consequences.

"Ultimately," Ball said, "we want this discovery to benefit growers and consumers."