Issue link: http://winesandvines.uberflip.com/i/987926
28 WINES&VINES June 2018 I n 1999, vine deaths in large portions of vineyard acreage in Temecula made it clear to the California wine industry and state, local and federal agencies that the glassy- winged sharpshooter's (GWSS) vectoring of Pierce's Disease (PD) put the entire state grape crop at risk. The next year, the California Department of Food and Agriculture established the Pierce's Disease Control Pro- gram (PDCP) to work with the grape industry, the US Department of Agriculture, County Agricultural Commis- sioners, the University of California and other state and local agencies on this serious problem (see sidebar for program details). Due to the limited knowledge of PD and GWSS, the early emphasis was on funding research to develop new and better ways to manage the PD/GWSS issue. Recogniz- ing the need and value of addressing this problem, and with the federal and state governments spending millions of dollars to control the spread of GWSS, the California winegrape industry chose to shoulder its share of the fi- nancial costs. In 2001, an annual, value-based assessment on wine grapes was established, primarily to fund PD/GWSS re- search. To date the assessment has generated more than $55 million. PD/GWSS research successes cover a considerable range, starting with traditional management approaches such as containing the spread of GWSS, introducing and augmenting biological control agents for GWSS, and de- veloping PD-resistant red and white grape clones. New approaches included inoculating vines with a benign strain of Xylella fastidiosa (Xf; the pathogen causing PD) to prevent the colonization of the naturally oc- curring virulent Xf strain; using a mixture of bacteriophages that kill Xf, and applying a chemical called diffusible signal factor to vines to prevent Xf from moving and spreading. (The results from every PD/GWSS assessment- funded research project from the research symposium proceedings are posted at https:// www.cdfa.ca.gov/pdcp/research.html.) A very important milestone in PD/GWSS research was the University of California, Davis (UCD) Foundation Plant Ser- vices' 2017 pre-release of five wine- grape clones highly resistant to PD to participating nurseries. Wine has been made from each one and subjected to de- tailed tasting. They were developed by Dr. Andy Walker of UCD's Department of Viticulture and Enology using con- ventional breeding practices. New genomic techniques enabled Walker to identify PD-resistant genetic markers within months of seed germination so that new backcrosses could be made quickly. This resulted in a significant short- ening of the standard breeding timeframe to develop PD- resistant vines that then could produce fruit to make wine for tasting trials. The clones are not yet available to growers while intellectual-property aspects of the new clones are addressed (See table pg. 29). Assessment-funded research has produced several novel approaches to managing PD/GWSS. The University of Florida's Dr. Don Hopkins identified a benign strain of Xf that, when present in a grapevine before colonization by the natural virulent strain, prevents the development of PD if the vine subsequently becomes infected by the virulent strain. Dr. Hopkins is working with a private company to develop this practice commercially. More recent research by Cal-Berkeley's Dr. Steve Lindow has identified a diffusible signal factor (DSF) that is pro- duced by Xf during the later stages of vine colonization. When Xf first enters the vine, it moves around through the plant's xylem system. When populations build up, the con- centration of DSF also builds up, signaling the bacterium Vineyard View n CLIFF OHMART Pierce's Disease Control Program Research Successes Clones 09314-102 (left) and 09331-047 are two of the Pierce's disease resistant clones bred by Dr. Andy Walker but have yet to become commercially available.