A group of researchers from Texas A&M University believe they have developed a novel and environmentally friendly solution to one of the wine industry’s more troubling threats: Pierce’s disease. They hope to target the bacterium behind the disease with bacteriophages—viruses that specifically attack bacteria.
Pierce’s disease is caused by Xylella fastidiosa, a bacterium that comes in multiple strains and poses a threat to more than 200 types of plants, including grapevines and many fruit trees. The bacterium spreads easily and quickly, entering the plants with the help of insects. Various subspecies of xylella attack different plants, travel on different insects and cause different diseases. The strain behind Pierce’s disease, which forms a gel in vines’ xylem, choking the plants of nutrients, originated in the American South. The illness began to spread rapidly through California vineyards in 1996, thanks to the arrival of the glassy-winged sharpshooter, a non-local insect.
With the recent discovery of a strain in Corsica and reports in California of sharpshooters appearing in vineyards that were not previously considered to be at risk, vineyard owners everywhere are anxious for a solution. California vintners have been focusing much of their energies on keeping the sharpshooter from spreading the bacterium, and scientists have been working on breeding grapevines resistant to xylella.
But at A&M AgriLife's Center for Phage Technology, a team has been studying the idea of a treatment employing bacteriophages. “Phages are a green solution. Pesticides target the vector, in this case the sharpshooter,” said Dr. Carlos Gonzalez, a professor who specializes in plant bacteriology.
“Paul Draper of Ridge Vineyards had a vision some years ago that phages could be used to protect vines from [Pierce's disease],” added Gonzalez. “We had ongoing research in developing a phage-based control for PD, so we joined together toward a common goal.”
Gonzalez says their lab is the first to isolate and propagate phages that target xylella. They next focused on finding virulent phages, ones that were especially deadly to the bacterium, eventually settling on four. Those four phages are mixed into a “cocktail” that has to be injected into each vine.
Despite the labor-intensive method, the results have been promising. Gonzalez and his team injected the cocktail into vines in a greenhouse lab, both vines that were already infected by xylella and ones that were still healthy. The vines that did not have the disease at the time of inoculation were protected against infection, and just as important, vines that were already infected showed a halt in symptoms after inoculation.
Gonzalez cautions that this solution, as promising as it is, is still at least three years away from being a commercially viable solution. “We still need to conduct field trials in California, and then go through the regulatory process, which could take another 12 to 18 months,” he said. Nor should it be viewed as the only solution to the problem of Pierce’s disease. “Our research is different than, say, the work being done by Dr. Andrew Walker at U.C. Davis, who is breeding new cultivars that are resistant to PD. We need all approaches, since nature evolves.”