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, except for Muscat Blanc which was initiated in 1996. Significant clonal differences wee measured in all of the cultivars as follows: Muscat Blanc. The Milan introductions Clones 3 and 4 were distinctly better than Clone 1, an older introduction into California. Clone 1 had fewer and heavier clusters with larger berries and more bunch rot. Clone 4 was of higher fruit maturation than Clone 3. No clonal yield differences were shown. 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 1A). Genetic differences have been more apparent than heat treatment differences, with Clone 3 producing the highest yield, lowest fruit maturation and most bunch rot. Although differences among Clones 1A and 2 were minor, Clone 2 is preferred at this point, due to its best overall fruit composition, as well as acceptable yield. Sangiovese. This cultivar continues to show rather distinct clonal differences, with Clone 2 continuing to show the greatest promise due to its smaller berry size, good fruit composition, and high vine fruitfulness and yield. Clone 3 has the largest berries, fewest clusters, and lowest yield; Clone 4 has the poorest fruit composition and most bunch rot. Muscat of Alexandria. The California selection A3 is out-yielding both its Australian counterparts – J2 and G5 – with comparable to superior fruit composition. Differences between the Australian clones were finally apparent in 1996, with J2 being more fruitful but with smaller berries of lower soluble solids than G5. Two more years of data collection in these trials are anticipated in order to determine consistency of differences over time. Propagation material has been obtained and the trial plots have been marked out for the Chardonnay, Cabernet Sauvignon, Merlot, and Zinfandel trials to be planted in 1997.