Explore Magazine Volume 6 Issue 2


Technology Creates Pierce's Disease-Resistant Grapevines
by Aaron Hoover

Grape growers battling a disease that causes millions of dollars in losses each year — and also prevents the cultivation of popular grape varieties in the Southeast — may soon be able to turn to genetically modified plants that resist the disease.

On May 15, the U.S. Patent and Trademark Office issued a patent for the use of a group of genes in grapevines expected to make the plants resistant to Pierce’s disease, for which there currently is no effective control. The patent was issued jointly to the University of Florida and the U.S. Department of Agriculture, who collaborated several years ago to develop the technology to transfer one of the genes into the plants. The research has since continued at UF’s Institute of Food and Agricultural Sciences as part of multimillion-dollar project.

“We believe these genes could protect grape plants against a number of diseases, but our target is Pierce’s disease,” said Dennis Gray, a UF professor of developmental biology at the UF Mid-Florida Research and Education Center in Apopka. “We had promising results early on in the project, and we’re optimistic tests will confirm heightened resistance in the plants.”

With grapes ranked among the top 15 most valuable crops in the nation, Pierce’s disease-resistant grape plants could have major benefits for the wine- and table-grape industries, Gray said. The disease has caused millions of dollars in damage in California.

The genetically modified plants could reduce or eliminate the use of insecticides in California aimed at killing insects that spread disease. Such insecticides provide, at best, temporary relief, according to UF research dating back to the 1920s, Gray said. Another advantage of the genetically modified plants is that they could open the door to growing more valuable wine- and table-grape varieties in the southeast and Florida, he added.

Pierce’s disease is caused by a species of bacterium that lives exclusively in the water vessels of a variety of plants. The strain that lives in grapevines clogs the vessels, causing the plant to dry up and die. First detected in southern California in 1884, the disease had been a minor problem in West Coast viticulture for decades. In the mid-1990s, however, it became prevalent in southern California and began marching steadily northward.

Scientists have tied the spread to the emergence of the bacterium in an insect, the glassy-winged sharpshooter, that has a much broader flight range than that of previous Pierce’s disease-carrying insects in California.

“The problem has just exploded in the past few years,” Gray said.

Pierce’s disease has another negative effect: It is endemic to the Southeast, where it prevents the cultivation of Vitis vinifera grape varieties — which include the world’s most popular wine and table grapes, Gray said. As a result, growers in Florida and other Southeastern states are restricted to native Muscadines or Pierce’s disease-resistant vinifera hybrids, he said.

Gray and Ralph Scorza, a USDA agriculturalist, had their first success in 1994 when they successfully transferred a lytic peptide gene into a Thompson Seedless vine, the nation’s most popular grape. The top-selling seedless table grape, raisin grape and wine grape, Thompson Seedless accounts for 40 percent of the U.S. grapevine acreage.

The genes are a synthetic version of those found in a variety of organisms, such as the silkworm larvae, which uses genes to kill bacteria and fungi, Gray said. In laboratory conditions, the protein produced by the gene kills the Pierce’s disease bacterium. The research has received about $4 million in funding. Supporters include UF and the State of Florida’s Viticultural Trust Fund, which provided more than $200,000 via the Florida Department of Agriculture and Consumer Affairs. ProfiGen, a Connecticut-based company focused on plant variety improvement, also has provided significant financial support and is the exclusive licensee of the patent. ProfiGen expects research to intensify.

Dennis Gray djg@mail.ifas.ufl.edu