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 potential FPMS source material. 1994 was the sixth and last year of evaluating three selections each of French Colombard and Chenin blanc. Each cultivar comparison involves two different selections which are registered (indexed as virus free) but not heat treated. Additionally, each cultivar includes a heat treated selection. Thus, we have been studying the possible influence of heat treatment on virus-free material of French Colombard and Chenin blanc. Barbera was in its fourth year of data taking. This compares an Italian selection, Rauscedo 6 (FPMS Clone 2), with Marshall (FPMS Clone 1). The Marshall clone presently involves much of the present commercial acreage but was found to contain mild leafroll after many plantings were completed. French Colombard. Overall, all three clones were fairly similar in response for consideration in commercial plantings. However, Clone 2 could be considered to be the most favorable selection due to minimal bunch rot problems and consistency in yield and fruit characteristics over the years of study. Differences due to heat treatment were found when comparing Clone 1 (no HT) and Clone 2 (91 day HT). Clone 2 had heavier berries, fewer berries per cluster, and a trend towards lower bunch rot incidence as compared to Clone 1. There were no significant differences in wines made from the clones in 1993. All three clones are being maintained by FPMS with Clone 2 “Registered” for qualification as California Foundation Stock. Chenin blanc. Clonal and heat treatment differences were greatest with Chenin blanc. Heat treatment resulted in higher cluster numbers and yield with Clone 4 and without corresponding negative effects on fruit composition. For this reason, Clone 4 is recommended above non-heat-treated Clone 1. Clone 5 was a big disappointment. Its higher cluster numbers with smaller berries and clusters were thought to be potential characteristics for lower bunch rot and higher wine quality. However, the clusters were very compact and showed almost twice the bunch rot potential as the other clones. Also, sensory analysis comparisons of the wines in 1993 showed no significant differences. Currently, recommended Clone 4 is “Registered” for qualification as California Foundation Stock. Barbera. Clone 2 (Rauscedo 6) 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 has been some delay in fruit maturation, a higher potential for rot, and lower wine color with Rauscedo in past years. Differences were relatively minor in 1994, with no yield differences between the clones and with Rauscedo only having heavier berries and clusters as compared to Clone 1. One more year of field data and wine quality comparison will enable us to make a more definitive recommendation. The problems with Rauscedo point to the need to clean-up Marshall with shoot tip culture as well as the importation of additional Barbera clonal material. Grenache. Sangiovese. Muscat blanc. and Muscat of Alexandria. Trials with 3 clones each were established in 1993 and will begin fruiting for data collection in 1995.