New grape varieties promise pest resistance

Citing climate change and the idea it might repulse a well-documented vine disease, University of California, Davis, researchers have released new varieties of wine grapes.

The five new varieties, three red and two white, are highly resistant to Pierce's disease, which has been battled periodically in North Bay vineyards and which UC Davis states costs California grape growers more than $100 million a year.

The new, traditionally-bred varieties also produce high-quality fruit and wine, the creators of the new varieties states.

Ambulo blanc, one of two new white grape varieties, is similar to sauvignon blanc and has been tested in Sonoma, Temecula and Napa.

'People that have tasted the wine made from these varieties are extremely excited,' Andrew Walker, geneticist and professor of viticulture and enology at UC Davis, who developed the new Pierce's disease resistant varieties, stated in the university's announcement. 'They are impressed that they're resistant but also that they make good wine.'

Pierce's disease is caused by a bacterium spread by a group of insects called sharpshooters. It causes grapevine leaves to yellow or 'scorch' and drop from the vine. The grape clusters also dehydrate, and infected vines soon die. While the disease has been around since the beginning of wine grape production in California, concerns have escalated with the arrival of the nonnative glassy-winged sharpshooter, which has the potential to spread the disease more rapidly. Pierce's disease occurs most often near rivers and creeks, and around urban and rural landscaping where sharpshooter populations reside.

In 2015 and 2016, thousands of vines were pulled out in the North Bay after an outbreak of the disease and its carrier, the glassy-winged sharpshooter. The pests were discovered in Marin and Sonoma counties.

To create the new varieties, Walker crossed a grapevine species from the southwestern U.S. and northern Mexico, Vitis arizonica, which carries a single dominant gene for resistance to Pierce's disease and was used to cross back to Vitis vinifera over four to five generations. It's taken about 20 years to develop the five patent-pending selections that are now being released.

'So far there has not been tremendous interest in new wine grape varieties, but climate change may encourage growers to reconsider wine grape breeding as we work to address future climates and diseases.'

These five varieties are ready for patenting and release. There will be limited amounts of plant material available for propagation in 2020 as only a few of the grape nurseries participated in a pre-release multiplication program. The university stated much more will be available in 2021. The Pierce's disease resistance breeding program continues, and more selections are approaching release.