Wines & Vines

50 practical winery & vineyard March 2015 Vines in California were infected with the benign strain at three sites in 2008. Promising results were obtained in a Riverside test in 2013, but it is too early for conclusions to be made from that trial. Further work is now being con- ducted by a private company for possible commercialization of the benign strain. Four other methods that all involve genetic modification of the rootstock and not the scion have shown varying degrees of success in field trials. In each trial the roots were modified to create a protein or molecule that is passed across the graft and up into the scion to disrupt Xf and allow the vine to continue to thrive with little or no signs of PD. • Dr. Stephen Lindow at UC Berkeley discovered that Xf in plants is influenced by a small diffusible signal factor (DSF) protein that accumulates when cells are at high cell density. By enabling the vine to produce its own DSF, Xf bacte- rial reproduction is disrupted; its ability to efficiently colonize the grapevine's water-conducting tissue is interrupted, and PD symptoms are reduced or pre- vented. Lindow has also begun work on a DSF strain that could be used on exist- ing vineyards to prevent PD. • Dr. David Gilchrist at UC Davis is con- trolling programmed cell death (PCD) in grapevines from Xf. Research identified the genetic instructions that, if altered, resulted in suppressing PD symptoms in grapevines. Field trials have led to identification of two gene sequences that significantly reduce Xf in infected grape- vines. • Plant cell wall-degrading enzymes including polygalacturonase (PG) allow Xf to break cell walls and spread within the grapevine. Researchers discovered that some plants express their own PG-inhibiting proteins (PGIPs) to pro- tect themselves and limit the bacterium's ability to spread. Dr. John Labavitch and his UC Davis team discovered several such gene candidates, and they are now working to identify which will be the most effective in halting Xf in grape- vines. This research might also lead to a spray or drip system application for established vineyards. • Dr. Abhaya Dandekar at UC Davis found that a key feature of Xf is its abil- ity to digest pectin, permitting it to move within the grapevine. Proteins like poly- galacturonase-inhibiting protein (PGIP) and a chimeric antimicrobial protein have been proven to prevent or reduce the movement of Xf in grapevines. Two field trials showed that resistance created in the rootstock moves up into the scion. These genetically modified rootstocks have shown varying degrees of success and are continuing to be developed in field trials. Solutions are near It is hard to say exactly what form the solution to PD will take. With several of them in development, it may be a com- bination, or perhaps one or another may become preferred by region, variety or growing practices. During the 2013 Pierce's disease Research Symposium in Sacramento, Calif., Dr. Gilchrist said, "We are halfway down the field toward a touchdown, and the next step is critical. With a little bit of funding and hard work, we can turn our work into something practical." It is clear the growers' money has been well spent, and there is good reason. Al Rossini, a grapegrower from Denair, Calif., and a member of the PD/GWSS Board, says, "When the guys putting up the money are the same ones who are making the decisions, you get results." PWV G R A P E G R O W I N G

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