Clonal Testing of Wine Grapes in the San Joaquin Valley
The San Joaquin Valley wine cultivar clonal evaluation study was initiated in 1987. It is an ongoing study to evaluate the most promising, virus disease-free clonal material being held or introduced as FPMS source material. French Colombard, Chenin blanc, and Barbera were completed in 1994 and 1995. Trial blocks of 3 clones each of Grenache, Sangiovese, Muscat blanc, and Muscat of Alexandria were established in 1993; data collection was initiated at harvest, 1995, in these new trials. Significant clonal differences have been measured over 3 years in all of the cultivars as follows: Muscat blanc. The Milan introductions, clones 3 and 4 have been distinctly better than clone 1, an older introduction into California. Clone 1 had fewer and heavier clusters with larger berries, less fruit yield, and more bunch rot. Clone 4 was of higher fruit maturation than clone 3. Thus, clone 4 is the best performing selection at this point in the study. Grenache. These are all California selections. The trial includes a genetic comparison (Clone 1A vs. 3, both non-heat-treated) and a heat treatment comparison (1A vs 2, clone 2 being a 62-day heat treatment of Clone 1 A). Genetic differences have been more apparent than heat treatment differences, with clone 3 producing the highest yield, lowest fruit maturation and most bunch rot. Differences among clones 1A and 2 have been minor. While clone 2 has slightly better fruit composition, its rot potential was similar to Clone 3. Clones 1A and 2 are fairly comparable at this point. Sangiovese. This cultivar continues to demonstrate rather distinct clonal differences, with Clone 2 continuing to show the greatest promise due to its smaller berry size and high vine fruitfulness and yield. Clone 3 has the heaviest berries, fewest clusters, and lowest yield. Clone 3’s earlier ripening could be attributed to a lower crop load, as compared to Clone 2. Clone 4 has the poorest fruit composition and most bunch rot. Muscat of Alexandria. The California selection A3 has out-yielded both its Australian counterparts – J2 and G5 – with comparable fruit composition. Differences between the Australian clones were minor, with J2 having smaller berries than G5, overall. A3 was the most fruitful and vigorous, accounting for its high yield potential and fruit ripening capabilities. One more year of data collection in these trials is anticipated in order to determine consistency of differences over time. The Chardonnay, Cabernet Sauvignon, Merlot, and Zinfandel trials were planted in 1997 at the request of the AVF Research Committee. Six clones of each cultivar are to be compared for ‘fighting varietal’ data under warm climate conditions.