Clonal Testing of Wine Grapes in the San Joaquin Valley

This is an ongoing study to evaluate promising, virus disease-free FPMS clonal material for the San Joaquin Valley. Completion dates for past trials were: French Colombard and Chenin blanc (1994), Barbera (1995), and Muscat of Alexandria (1997), Grenache (1998), and Muscat blanc (1998). The Sangiovese trial was completed in 1999 with crop level comparisons. Data collection continued (2nd fruiting year in 2000) with the Chardonnay, Cabernet Sauvignon, Merlot, and Zinfandel/Primitivo trials. These trials were planted with 6 clones each in 1997 in order to evaluate clonal differences in a warm climate region. A new Barbera trial was planted in 2000.

Cabernet Sauvignon. Clones 2 and 24 again produced smaller berries and clusters than the others, as in 1999. This corresponded with lower yields and earlier fruit maturation. These characteristics tend to be more prevalent in Clone 2. The other clones ? 8, 10 ,21 and 22 ? were all similar.

Merlot. The Merlot clones showed significant differences in fruitfulness, berry weight, total vine yields, and fruit composition. Mostly, the differences were small. Some noteworthy responses included: heavier berries of lower pH in Clone 11; and lower vine yields from Clone 14 due to fewer clusters and smaller berries than some of the others. In contrast, Clone 10 produced 40%more yield than Clone 14 and with similar berry weight and fruit composition. Overall, Clone 10 performed very well, similar to Clones 3 and 9, except that it also produced smaller berries.

Zinfandel/Primitivo. Clonal differences were not as distinct as they were in 1999 when the Primitivo clones had smaller berries, fewer berries/cluster and clusters of lower mass and earlier ripening and less rot as compared to the Zinfandel clones. The Primitivo clone vine yields also tended to lower than those of Zinfandel in 1999. In contrast, the Primitivo clones tended to produced higher harvestable yields than those of Zinfandel in 2000, possibly due to less rot per cluster. Fruit soluble solids were higher in P3 and P6 as compared to 1A and 3. This is similar to the 1999 data showing earlier fruit maturation in the Primitivo clones as compared to Zinfandel. Titratable acidity was also higher in several of the Primitivo clones (P5 and P6) as compared to Zinfandel 2 and 3. Overall, clonal differences within the Zinfandel and Primitivo clone groups were small; they were greater between the two groups.

Chardonnay. Significant clonal differences were again measured in 2000, but the data is too preliminary to demonstrate important or consistent effects. For example, Clone 4 of outstanding performance in 1999, was of lower yield in 2000, the result of fewer clusters per vine. Vine yields were highest with Clones 15, 18, and 20 and lowest with Clones 4, 6, and 37. Yield differences could be largely attributed to differences in clusters/vine and/or cluster weight. Fruit maturation was largely influenced by total fruit weight. Clone 20 again produced the heaviest berries while Clone 6 produced the lightest clusters. The 2000 results of these trials are preliminary. They represent two years of data collection, the first of which was the 3rd leaf vine data in 1999.

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