By Dawn Dolan
Carrying a heavy economic burden for those areas of the country with infestation of the glassy winged sharpshooter (GWSS), Pierce’s disease is a plant pathogen, transmitted exclusively by sap-feeding insects. Brought to California in the 1980’s via a complicated pathway (PD was thought to have come from the Southeast, but it also seems to have come from Mexico, and likely spread north and split eastward and westward, based on the very different forms of resistance in the species from the SE compared to the SW), the spread of PD through the GWSS has led to economic devastation, with over 35,000 acres of Vitis vinifera (wine grape vines) being affected.
Under the oversight of the Pierce’s Disease/Glassy Winged Sharpshooter Board, created in 2001, over forty-five million dollars have been spent supporting Pierce’s Disease (PD) research over the past nineteen years.
Set for June 8th, results of the PD/GWSS referendum on whether to continue funding the research projects will be announced. Weeks ago, the wine industry was sent ballots and encouraged to vote on whether to continue to levy the self-assessment, and thereby continue to fund the PD research. Steve McIntyre, the only original board member still serving on the PD/GWSS board, explains the importance of ongoing funding, “We expanded the mandate of the program to include the mealy bug, the brown marmorated stink bug and red leaf virus over the last five years. We [the Board] are hoping the industry votes to self-assess and continue the funding. This would allow us to expand the scope of projects allocated for funding, while keeping the current projects going.”
All proposed projects are submitted and undergo a review, with the list of currently funded projects found in the Summer 2019 CDFA- PD/GWSS Board bulletin.
After over twenty years of study, some lights are finally turning on for growers in PD-infected areas of the country in the areas of resistant vine creation, therapeutics, and also with pest mitigation.
“We originally wanted to find a cure for PD, or be able to manage it with therapeutics,” says McIntyre. “We now have two promising therapeutics, to be commercialized within the next two years.” McIntyre says that Dr. Steve Lindow, from UC-Berkeley has been doing work on an antagonistic bacterium that can be applied to a grape vine and will clear the PD-causing agent from that vine.
On the vine side, Professor Andrew Walker, Ph.D. has two projects being funded by the PD/GWSS Board assessment. Working from University of California-Davis, his projects tackle the task of breeding PD resistant vines, and the molecular structure behind that breeding. “It all began with a fortuitous discovery of PD resistance in random vines,” chuckled Dr Walker. A native species, Vitis arizonica, was first collected in the 1960’s. His work on the genetic markers of PD led to the discovery that Vitis Arizonica had this marker. Starting from over a thousand samples, they narrowed it down to the five with the highest propensity for resistance.
The other therapy is an exciting platform technology, with indications that it could be used as a base upon which other applications are developed. Not only is it applicable for PD, this new therapy may also have broad spectrum applications. Touts McIntyre, “This AMP (antimicrobial peptide), may become the next generation of antibiotics for humans, plants and animals.”
“We were able to focus our energies more precisely, doing this over and over for generations,” notes Walker. Then he started crossing the PD resistant native vines with Vitis vinifera. Using an accelerated system to create a generation in two years, instead of 5-10 years or more, they crossed the native species with Cabernet, Zinfandel, Petite Sirah, Chardonnay and Sauvignon Blanc.
Carter Creek Winery Pierce’s Disease resistant vineyard planting
“At first we thought this [crossing] would just create a blending grape. We ignored the quality of the fruit until we got to a certain level,” says Walker, who held Pierce’s Disease resistance as the highest criteria in the cross. Then they started growing larger populations in the vineyard, looking at fruit quality, then wine quality. “It took fifteen years,” cites Walker, but they now have grapevines that are 97% Vitis Vinifera, which are indistinguishable in wine-making quality from full Vitis Vinifera, and retain the PD-resistance trait. They are producing good quality, stand-alone varietal wines.
“None of this would have been possible without the funding from the PD/GWSS Board’s funding”, says Professor Walker. An expensive endeavor, this project needed the space, labs, and field crews to make it run. But with another possible ten varietals in the works, areas of the country which currently have had to use heavy spraying techniques to make wine grapes work for them will now have another option.
Dustin Hooper, VP of Sales at Wonderful Nurseries, has just sent off the first set of PD-resistant vines. “We got them [the resistant vines] in 2018 on a test agreement with the USDA. We’ve been establishing them, and now we’ve gotten the okay to go ahead and sell them.” With their mother block established, they have shipped their first lot of vines to Texas, two varietals; Errante Noir & Paseante Noir.
The journey has been long for the commercial vines. Says Hooper, “We’ve had a waiting list for four years, so we put people on that list, and they had to wait for us to be approved.” Hooper notes that their waiting list includes vineyards from all over the US, including Texas, Northern California, Temecula, East Coast, and South-Eastern vineyards as well.
As far as his nursery production goes, Hooper notes that, “Our nursery is located in a non-Pierce Disease quarantine area, so we don’t have the vector spread in our area, and we’ve had no positives in our nursery for over 20 years.” He assures that they take extreme care in their nursery with processes implemented as if they were in the quarantine zone. As to the cost of the vines, he says, “These varieties are more expensive, as there is royalty paid to the USDA of $1.00 per vine.”
Now that these PD-resistant vines are available, Hooper says Wonderful Nurseries will start ramping up production. Shipping vines all over the US and globally, and these PD-resistant vines will add to their portfolio. States Hooper, “If PD pressure continues to grow, we may get more orders. We want to serve the growers.”
If the newest round of funding is approved, McIntyre is hopeful that the expanded scope of work will bring more results, like the previous funding has. “We’ve also been able to confine the GWSS to an area of Southern California, and now with this new antimicrobial peptide, we might have developed something that will also help save animal and human lives.”