Clonal Testing of Winegrapes in the San Joaquin Valley

A San Joaquin Valley wine cultivar clonal evaluation study was initiated in 1987. It utilizes 15 single-vine replicates in randomized complete blocks for each cultivar at the UC Kearney Ag Center. 1993 was the fifth year of comparison for three selections each of French Colombard and Chenin blanc. Each cultivar compares two different selections which are registered (indexed as virus free) but not heat treated. Additionally, each cultivar includes a heat treated selection. Thus, we are studying the possible influence of heat treatment on virus-free material of French Colombard and Chenin blanc. Barbera was in its third year of data taking. This compares an Italian selection, Rauscedo 6 (FPMS Clone 2), with Marshall (FPMS Clone 1). Barbera Clone 1 presently involves much of the present commercial acreage but was later found to contain mild leafroll. French Colombard. Clones 1 and 2 showed no significant differences in vine fruiting responses which is similar to the 1992 results. Thus, these two selections of the same genetic source but comparing no heat treatment (clone 1) vs. a 91 day heat treatment (clone 2) are now of similar performance. This is in contrast to the first two years (1990 and 1991) of data taking when clone 2 appeared to be the best selection due to more favorable fruit composition. In contrast, clone 5 had significantly lower soluble solids in 1993 and a trend toward smaller berries, heavier clusters, and higher yields as has been demonstrated in previous years. No differences in sensory analysis of the wines made from these selections in 1993 were shown. This trial will be summarized after the 1994 harvest. Chenin blanc. Clone 5 again produced the smallest berries and clusters of earliest maturity. However, the yields are lower and the bunch rot is higher with this selection. Clone 1 and 4 were similar in performance in 1993, although clone 4 has out-yielded clone 1 in the past. Sensory analysis comparisons of the wines showed no significant differences. A 6-year summary of this trial will be completed after the 1994 harvest. Barbera. Clone 2 (Rauscedo) would appear to be the recommended choice for future planting, given its virus-free status and higher yields as compared to clone 1 (Marshall). However, there is some delay in fruit maturation, a higher potential for rot, and possibly lower wine color with clone 2. Significant differences for wine taste and aroma of these selections were found but could not be consistently characterized. One more year of field data and wine quality comparison will enable us to make a more definitive recommendation. The problems with clone 2 point to the need for importation of additional clonal material for evaluation. Grenache. Sanqiovese, and Muscat blanc. Trials with 3 clones each were established in 1993 and are being trained in 1994.