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. Data collection continued (third fruiting year in 2001) 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 and trained in 2001.

Chardonnay. Clone 4 was high yielding in 2001, as in 1999; its cluster numbers and yields were lower in 2000, suggesting an alternate bearing response. Clone yield differences in 2001could be largely attributed to differences in berries per cluster and cluster weight. While Clone 4 had the fewest clusters, they were the heaviest due to high berry numbers per cluster; its fruit composition was again among the best – – high soluble solids and TA, and low Ph. Clone 20 also tends to be high yielding, but with heavier berries of lower soluble solids. Clone 15 had the fewest berries per cluster and the lowest bunch rot incidence in 2001; it was also lowest yielding.

Cabernet Sauvignon. Clone 2 again had the fewest clusters and smallest berries. Clone 24 was also more similar to Clone 2 than the others. The others were similar to one another except for the heavier berries and higher fruit Ph of Clone 22. While the overall differences were not great, the trend toward smaller berries with Clones 2 and 24 and the larger berries of Clone 22 may be of importance to San Joaquin Valley growers. However, the smaller berry characteristics are accompanied with some sacrifice in yield, unless pruning practice can compensate for the lower cluster numbers in Clones 2 and 24.
Merlot. The Merlot clones showed significant differences in all of the measured parameters. Clone 11 produced the heaviest berries with the highest bunch rot. It also produced the highest fruit Ph in 1999 and 2000, all of which are undesirable characteristics for warm districts. Clone 14 again produced fewer clusters with smaller berries than some of the others, with corresponding lower vine yields and higher oBrix. Clone 10 was the most fruitful and had the highest fruit TA. It has also performed well in all yield and fruit composition parameters in previous years. Thus, Clone 10 has consistently shown good characteristics, while Clone 11 shows some unfavorable characteristics for warm climates. While Clone 14 has small berries, its lower yield is a disadvantage, unless this can be improved with higher pruning levels.
Zinfandel/Primitivo. Clonal differences were again 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. However, the Primitivo clones continue to show some advantages over the Zinfandel clones in terms of higher cluster numbers, higher fruit %soluble solids, smaller berry weights, and much less bunch rot in one clone, Primitivo 6. Primitivo 3 is again showing the highest yield potential of all of the selections, and with good fruit composition. Overall, clonal differences within the Zinfandel and Primitivo clone groups were small; they were greater between the two groups.
The clonal variations in response over time point to the importance of multiple year data collection in excess of 2 years of full production. At least 4 years of full production data are needed to determine longer term vine response.

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