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Figure 4. Ripening cluster size, 2019.

A multi-year research and breeding project conducted by Andy Walker, a grape breeder at UC Davis, led to the development and release of five new grapevine cultivars. The new cultivars include three red wine grape selections and two white wine grape selections that have repeatedly shown strong resistance to Pierce’s Disease in greenhouse and field trials. The new releases have shown high fruit quality and high wine quality across several vintages and in wine tastings.

During his visit with the Alabama grape growers earlier this year, Walker explained that his lab has been traditionally-breeding wine grape varieties of Vitis vinifera (known as European or French grapes) with native American Vitis species that carry PD-resistant genes. The five new releases carry a PD-resistant gene from Vitis arizonica. Walker used traditional breeding methods that involve the backcrossing through several generations of vine crosses to progressively increase the European grape parentage and characteristics to as high as 97% within the final resulting cross. Each generation carries resistance genes.

What is the significance of the new varieties for Alabama and the Southeast? PD-resistant cultivars could be highly sought after and widely accepted for commercial use in the Southeast where growers are currently limited to growing currently available PD-resistant hybrids that do not have V. vinifera wine quality.

Research trials were established at Auburn University in 2010 with earlier generations of UC Davis developed PD resistant European grapes to study the feasibility of their cultivation in Alabama’s warm and humid environment. The 9-yr results are very promising in terms of grape productivity, fruit quality and resistance to PD and suggest the newly developed grape progeny have the potential to greatly sustain the viticulture industry and broaden the window of economic opportunities especially for small- and medium-size family farms. The adoption of these innovative grapevines started in Alabama a few years ago when two commercial vineyards were granted the license to grow some of the PD resistant European grapes.

Varieties

Walker provided the following descriptions of the five patent-pending varieties:

07355-075 – 50% Petite Sirah, 25% Cabernet Sauvignon

This red wine grape makes wines with characteristics of both Cabernet Sauvignon and Petite Sirah. It is established in large test plots along the Napa River and commercial scale wines have been made from this plot. This selection is one of the earliest to break dormancy and it also blooms and ripens early. The berries are relatively large and the well-filled clusters are medium in size. This selection has been repeatedly tested in greenhouse screenings and is highly resistant to PD. It is one of the few selections that will be released at the 94% V. vinifera level, and has ranked highly at numerous tastings of both Davis and Napa grown fruit.

Tasting notes include: dark-red purple color, bright red fruit, raspberry, cherry, ripe, tannic, and elegant rather than dense.

09331-047 – 50% Zinfandel, 25% Petite Sirah, 12.5% Cabernet Sauvignon

This red wine grape is 97% V. vinifera and is highly resistant to PD. It is established in field trials in Temecula and along the Napa River, where commercial scale wines have been made. It blooms relatively late, but ripens mid-season. The berries are medium-sized and the clusters are well-filled and relatively large. Although this selection is spur fruitful it typically has only one cluster per shoot and is more productive with cane pruning. Wines from this selection have been ranked highly at numerous tastings of Davis and Napa grown fruit.

Tasting comments include: medium dark red with purple, berry pie, cassis, black olive, herbal, dried hay, coffee, vegetal like Cabernet Sauvignon, licorice, round, moderate tannins, and soft finish.

09356-235 – 50% Sylvaner, 12.5% Cabernet Sauvignon, 12.5 %Carignane, 12.5% Chardonnay

This red wine grape selection is 97% V. vinifera and is also highly resistant to PD in repeated greenhouse and field evaluations. It has a mid-season bloom and ripening period and has relatively large berries and loose clusters. It is highly productive. Wines have only been made from Davis fruit but ranked very highly.

Tasting comments include: dark-red purple color, complex fruit with herbs and earth, plum, big wine, dense, rich middle, and tannic yet balanced. This selection was also chosen by winemakers to have great blending potential with Cabernet Sauvignon. They also noted its high levels of high quality tannin.

09314-102 – 62.5% Cabernet Sauvignon, 12.5% Carignane, 12.5% Chardonnay

This white wine grape is 97% V. vinifera and highly resistant to PD after repeated greenhouse evaluations. It has been tested in Temecula, Sonoma, and along the Napa River. It has an early bloom and the fruit ripens early. It has small to medium berries and relatively large clusters. It is also highly productive. The wines are reminiscent of Sauvignon blanc.

Tasting comments have included: light straw to clear color, citrus, lime, tropical, gooseberry golden delicious apple flavors, bright fruit, slightly bitter, and textured.

09338-016 – 62.5% Cabernet Sauvignon, 12.5% Chardonnay and 12.5% Carignane

This white wine selection is also highly resistant to PD after repeated greenhouse evaluations. Wines have been made from Davis fruit, but it has not been planted in other field trials to this point. It has small berries and small compact clusters. It blooms relatively late and ripens mid-season. The vine has medium productivity. Growers have made wines from Davis-grown fruit and they have ranked well.

Tasting comments include: light straw-gold color, apple-melon, lychee, floral aromas, pineapple, green apple, juicy, harmonious, and well-balanced.

Additional Source: Wine Business Monthly, Dec. 3, 2019

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