(Wines&Vines) - The Napa Valley Grapegrowers, Napa Valley Technical Viticulture Group and University of California Cooperative Extension joined forces March 4 to present a summary of new findings about pests and diseases as part of the Grapegrowers’ Sustainable Vineyard Prices series.

Andy Walker of the University of California, Davis, Department of Viticulture & Enology discussed using the lessons learned from breeding grapes for resistance to Pierce’s disease (PD) to produce grapes resistant to powdery mildew. While creating a vine with that resistance is challenging, he reported significant progress breeding PD-resistant vines and says they will be ready for planting in a few years.

While maintaining the resistance to PD, Walker is also trying to breed grapes resistant to powdery mildew and to combine powdery mildew resistance with PD resistance. Powdery mildew is a North American fungal disease.

V. vinifera is susceptible, and vineyards are protected by application of fungicides at seven- to 21-day intervals; failure to apply fungicides can result in complete crop loss.

All North American native Vitis species resist powdery mildew to some extent, but resistance also exists in V. romanetii, V. piasezkii from China, and in some Central Asian V. vinifera varieties including Karazdhandl, Kishmish Vatkana and a few others Walker’s lab has discovered.

Many resistant hybrids with North American grapes exist, but they do not have vinifera fruit quality, and most have complex resistance difficult for breeding.

Australian and French researchers found single-gene resistance to powdery mildew in the muscadine grape, M. rotundifolia. Walker’s group is using these sources and those from China and Central Asia to stack resistance genes and produce wine grapes with durable resistance to powdery mildew, and to incorporate it with PD resistance.

They know that grapes will need multiple resistance genes and have mapped a wide range of resistances to different chromosomes, making it possible to combine and follow multiple unique resistances. Dario Cantu, a new genomics specialist in the Department of Viticulture & Enology at UC Davis, is aiding these efforts.