Winegrape Trials for Pierce's Disease Begin

Research symposium reviews several strategies to target the grapevine scourge

by Jon Tourney
Don Hopkins PD winegrape
Researcher Don Hopkins of the University of Florida presents an update on his project to control PD with a benign strain of Xylella at the PD Research Symposium.

Sacramento, Calif. -- After 10 years of funding research on Pierce’s disease (PD) through assessments collected from the California winegrape industry, the California Department of Food and Agriculture (CDFA) Pierce’s Disease/Glassy-winged Sharpshooter Board’s research projects aimed at producing PD-resistant grapevines have entered the field trial stage.

These promising results and other research progress reports were highlighted at the 2009 Pierce’s Disease Research Symposium, a two-day rendezvous of researchers from throughout the United States held in Sacramento last week. Since 2001, California’s PD/GWSS Board has spent $19.3 million on research. Nationally, $100.6 million has been spent on PD research during the same time period from all funding sources, the majority from federal appropriations.

Breeding or inducing resistance in grapevines to the PD bacterium Xylella fastidiosa (Xf) is considered a long-term solution to maintain vine health in the field while reducing or eliminating the need for pesticide use to control GWSS and other PD vectors. Field trials are under way with biocontrol-treated vines and traditionally bred vine material. Field trials are planned to begin in 2010 with transgenic vine material.

Biocontrol field trials
Dr. Donald Hopkins, professor of plant pathology at the University of Florida’s Mid-Florida Research & Education Center, has been evaluating the use of a benign strain of Xf -- labelled EB92-1 -- isolated from elderberry in Florida and found in grapes and other host plants. Hopkins’ work to date shows that the EB92-1 can colonize in a grapevine, similar to other strains of Xf bacteria, but without causing PD symptoms or vine health problems, and it can prevent or reduce PD symptoms from pathogenic Xf strains. Vines in a Florida field trial (Syrah on Freedom rootstock) in a location with moderate to high PD pressure were inoculated with EB92-1 prior to planting and still show no PD symptoms after 13 years in the field.

A field trial was started in Temecula in July 2008, and additional trials were started in Napa and Sonoma Counties during the past year. The Temecula trial involves Cabernet Sauvignon and Orange Muscat on 110R rootstock in a vineyard with extreme PD and GWSS pressure.

The trial in Napa Valley (Riesling and Chardonnay on 3309 rootstock) and the trial in Sonoma County (Barbera and Viognier on 110R rootstock) are in vineyards near riparian areas that have PD pressure and populations of blue-green sharpshooters.

In the Temecula trial after one year, both the treated and untreated vines have shown PD symptoms, although the EB92-1 treated vines appeared to have milder symptoms than the untreated vines. However, Hopkins said that in previous trials in Florida and Georgia, PD symptoms also commonly occurred in treated vines during the first year after planting, and beneficial effects from the biocontrol strain did not begin to appear until the second year after planting.

Hopkins also is conducting trials in North Carolina and began a trial in Texas in 2009. Southeastern states, where vinifera varieties cannot be grown in most areas due to endemic PD and vectors, also would benefit from this research with the ability to produce higher quality and more popular vinifera grape varieties.

The current inoculation method is to needle-inject the stem of every young vine with a suspension of the EB92-1 strain, either in the field at the time of planting, or in the nursery greenhouse just prior to planting. Since this is labor intensive, Hopkins is evaluating the possible use of mother vines with the biocontrol strain as propagation material for scion wood or rooted cuttings, to see if the strain can be transmitted through scion wood.

Hopkins also has trials to test whether mature vines with PD pressure can be inoculated with EB92-1 and show improved resistance. Hopkins believes, “The successful completion of the biocontrol tests in Temecula, Sonoma and Napa would lead to an effective control of PD that is environmentally friendly. This project should yield results within the next two years, and if the control is successful, there should be a biological control for PD available for commercial use in vineyards in California.”

Breeding PD-resistant winegrapes
Dr. Andy Walker at UC Davis is using traditional breeding methods to produce crosses of vinifera varieties with the Xf-resistant Vitis arizonica/candicans grapevine sourced from Mexico. After successive generations of crosses and back-crosses, the percentage of vinifera parentage with the PD-resistance trait within advanced selections has increased to 88%, then 94%, and now 98% (for more on Walker’s research, see winesandvines.com/template.cfm?section=news&content=47484).

Field trials with the 88% and 94% vinifera selections have been planted in Napa Valley, and the 98% vinifera seedlings are scheduled for field trial planting in spring 2010. Individual vines are injected with Xf in the spring to evaluate PD resistance.

Walker said that PD-resistant vines show suppression of disease symptoms and suppression of Xf movement through the vine. Wines produced from small amounts of resulting grapes from the 88% vinifera in 2007 and 2008 were favorably evaluated. Wines were made in fall 2009 with the 94% vinifera that will be evaluated in the near future. Other PD-resistant source materials are being studied in order to better understand PD resistance and potentially provide a more diverse set of PD-resistant rootstocks in the future.

Transgenic field trials planned
Experimental field trials will be planted in spring 2010 to test three promising new transgenic plant technologies for PD-resistant grapevines developed by researchers at UC Davis and UC Berkeley. These have shown positive results in laboratory and greenhouse trials. These technologies involve alterations of grapevine plant material at the gene and cell levels to suppress or inhibit PD symptoms or to inhibit the colonization and movement of the Xf bacterium. UC Davis, UC Riverside, Texas A&M University in Fredericksburg, Texas, and Florida A&M University in Tallahassee, Fla., are being considered for field trials.
The Public Intellectual Property Resource for Agriculture (PIPRA) at UC Davis, under contract to handle technology transfer of board research to commercial applications, is evaluating costs and suitability for field trials at each location. PIPRA is handling the field trial permit application process with the U.S. Department of Agriculture (USDA).

In a presentation at the symposium, PIPRA executive director Alan Bennett discussed the regulatory and intellectual property hurdles involved with moving transgenic technologies to commercialization. Transgenic crop products that have been granted deregulated status by the USDA Animal and Plant Health Inspection Service (APHIS) for use in the U.S. include canola, corn, cotton, soybeans, potato, squash, sugar beets, tomato, papaya and plum.

Transgenic field trials are being conducted with a number of other crops throughout the country. The papaya and the plum are the only two tree crops to make it through the regulatory process to date. Bennett said it took nine years for the plum product (the HoneySweet Plum Tree developed for resistance to plum pox virus) to achieve deregulated status.

Proceedings from the 2009 Symposium with updates on current projects are accessible at cdfa.ca.gov/phpps/pdcp/2009_Research_Proceedings.html. A comprehensive source of information on PD research is at piercesdisease.org.

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