Assessment of Pierce’s Disease Resistant 87.5% Vitis vinifera L. Selections in Central Alabama

Goals: Bunch grape production in the southeastern United States is limited by the endemic bacterium Xylella fastidiosa, causal agent of Pierce’s disease (PD). University of California, Davis-bred PD-resistant 87.5% Vitis vinifera L. winegrape selections represent a new technology that can help sustain the viticulture industry in the southeastern U.S. by reducing pesticide inputs and diversifying grape production. PD-resistant vines were planted to determine viticultural performance and survival in central Alabama. We anticipated our results would indicate whether regional growers could feasibly grow PD-resistant, predominantly V. vinifera winegrapes under humid southeastern U.S. viticulture conditions.

Key Findings:

• All evaluated selections grew vigorously under humid southeastern conditions. U0501-12 produced the highest pruning weight during the 2015 to 2016 period of study. U0502-10 was the most productive selection, as measured by total yield per vine, and had the largest clusters. Harvest soluble solids content was highest for selection U0501-12, while titratable acidity was lowest for U0502-01.

• All selections broke bud prior to historical late-spring frost-risk dates, although no injury was experienced in the years evaluated. U0502-10 began veraison between one and two months earlier compared to the other selections in both years. U0502-10 was also harvested 70 and 22 days prior to the next selection in 2015 and 2016, respectively.

• The experimental vines neither exhibited symptoms nor tested positive for PD during vine establishment. Under regional commercial management practices, no vine losses resulted from other pathogens. However, an aggressive disease management strategy will be mandatory to produce consistently clean fruit in the humid southeastern U.S.

Impact and Significance: These results indicate grapevines with predominantly V. vinifera background can survive under humid viticulture conditions in central Alabama with the incorporation of alleles for PD resistance. Further research is necessary to refine management practices enabling sustainable production in the southeastern U.S. as PD-resistant grapevine cultivars become commercially available to regional producers.