Three clones of Malbec (Vitis vinifera L., syn. Cot) from Foundation Plant Services (FPS) were evaluated in Oakville, Napa Valley, California. Clones FPS 4, FPS 6, and FPS 8 were grown on two rootstocks, 110 Richter (110R) and Teleki 5C (5C). Vine yield components, fruit composition, and vegetative growth were measured over four growing seasons, 1997 through 2000. Shoot number per vine was held constant for all clones in a given year. Yield per vine, berries per cluster, cluster weight, clusters per shoot, and cluster number differed significantly among clones and between rootstocks. Berry weight differed significantly among clones, but not between rootstocks. All yield components varied significantly over the four vintages. FPS 8 had the highest yield and yield components, while FPS 6 had the lowest. Rootstock 110R had significantly higher yield than 5C by having more clusters and more berries per cluster. Yield component berries per cluster was most strongly correlated with yield differences. Pruning weight was inversely related to yield, where FPS 8 had the lowest pruning weight and FPS 6 the highest. The Ravaz index (yield to pruning weight ratio) was highest for FPS 8 and lowest for FPS 6. In years of greater yield, FPS 8 had greater soluble solids than FPS 4 or 6.
Malbec (Vitis vinifera L.), also known as Cot, is believed to have originated in the Lot Valley near Cahors, southeast of Bordeaux, France (Leclair 1995). Malbec reportedly fell out of favor in France in the late 19th century largely because of poor fruitset, an outcome attributed to virus infection. Clonal selection of clean stock eventually produced selections with “acceptable berry set” (Leclair 1995). Today Malbec is used primarily as a blending variety in Bordeaux wines.
Malbec plantings in California have increased steadily over the past 20 years, but the cultivar still accounts for only about 500 hectares (CASS 2005). Acceptance of Malbec by growers is limited because the variety is subject to “coulure,” or low fruit set (Christensen et al. 2003). Malbec clones have been certified by Foundation Plant Services (FPS) at the University of California, Davis (UC Davis), but have not been characterized as to their viticultural attributes, particularly yield. Thus, it was unclear whether a Malbec clone with consistent and acceptable yield could be identified among currently certified clones. Previous evaluations showed differences in yield, vegetative growth, and fruit composition among California certified clones in cultivars such as Chardonnay (Wolpert et al. 1994), Cabernet Sauvignon (Wolpert et al. 1995), Merlot (Benz et al. 2006), and Zinfandel (Wolpert 1996). Numerous studies have also shown that rootstock choice can enhance or diminish various scion growth characteristics (Ezzahouani and Williams 1995, Koblet et al. 1994, Nadal et al. 1995, Zelleke and Kliewer 1979). Hence, poorly performing clones of Malbec might be improved by rootstock.
The purpose of this trial was to evaluate whether any of three certified FPS Malbec clones had an acceptable yield and whether their performance was affected by grafting onto two commonly used rootstocks. To our knowledge, this is the first evaluation of Malbec clones in North America and the first trial where clonal selections were tested for their interaction with rootstock.
Materials and Methods
Three Malbec clones from Foundation Plant Services, UC Davis, FPS 4, FPS 6, and FPS 8, were evaluated for viticultural performance (Table 1⇓). Each clone was grafted onto two rootstocks chosen for their popularity in the Napa Valley, 110 Richter (110R; Vitis berlandieri x V. rupestris) and Teleki 5C (5C; V. berlandieri x V. riparia).
Vines were planted in 1992 at the Oakville Station Vineyards, in Oakville, Napa Valley, operated by the Department of Viticulture and Enology, UC Davis. The soil type was a deep, gravelly, Bale clay loam with a 0 to 2% slope (Lambert and Kashiwagi 1978). Vines were planted to a spacing of 2.4 m between vines and 3.0 m between rows, equivalent to a vine density of 1389 vines/ha. Vines were pruned to 11 shoots per meter on a bilateral cordon and trained to a vertical shoot-positioned (VSP) system. The cordon wire was 90 cm aboveground, with two sets of dual shoot positioning wires fixed at 135 cm and 180 cm aboveground. A drip system provided supplemental irrigation. All cultural practices were consistent with those for red wine varieties in Napa Valley.
Data collection began in 1997, when vines were mature and continued through 2000. Treatments were harvested on the same date. At harvest, clusters were counted and vine crop weighed. To be counted, a cluster was defined as one with 10 berries or more. Prior to harvest, one 100-berry sample was taken per treatment-replicate. Samples were returned to the laboratory and weighed to determine average berry weight. Berries were crushed and juice was filtered with cheesecloth. Soluble solids were measured as degree Brix with a hand-held, temperature-compensating refractometer. Juice pH was measured with an electronic pH meter, and juice samples were titrated with 0.1 N NaOH to a pH 8.2 end point to determine titratable acidity (TA). Juice potassium (K) concentration was determined by flame emission on a 1 to 100 dilution of the juice using a PerkinElmer 2380 atomic absorption spectrophotometer PerkinElmer, Shelton, CT) (Ough and Amerine 1988).
During dormancy, shoots on each vine were counted and dormant prunings were weighed. These values were used to calculate the average weight per shoot and the Ravaz index (RI, also called yield:pruning weight ratio). The experimental design was a randomized complete block, arranged as a split-split-plot, where rootstocks were main plots, Malbec clones were subplots, and years were sub-subplots. Twenty-seven vines were arranged as experimental units of three rows by nine vines with eight replicates. The centermost five vines of each replicate were used for data collection. Data were analyzed by analysis of variance (ANOVA) with mean separation by Duncan’s multiple range test (SAS Institute, Cary, NC).
Yield, averaged over four years of data, varied significantly among Malbec clones, with FPS 8 producing the highest, FPS 4 intermediate, and FPS 6 the lowest (Table 2⇓). All yield components showed the same relationship, with FPS 8 highest in clusters per shoot (2.2), clusters per vine (57), berry weight (1.91 g), berries per cluster (95), and cluster weight (180 g), while FPS 4 was intermediate and FPS 6 the lowest. On average, Malbec clones on 110R rootstock out-produced those grown on 5C rootstock (Table 2⇓) and involved all yield components except berry weight. Differences in clusters per shoot, clusters per vine, berries per cluster, and cluster weight for rootstocks were much less than differences among clones, that is, only about 10% higher for 110R than 5C. However, relative yield differences between rootstocks were not consistent among clones (Figure 1⇓), resulting in a significant clone by rootstock interaction.
Significant year-to-year variations in yield and all yield components were also found, with more than a four-fold difference between the overall average vine yield in 1998, the year of the smallest crop, and in 1997, the year of the largest crop (2.8 versus 11.4 kg/vine, respectively) (Table 2⇑). Relative differences among clones were not consistent across years, resulting in a significant year by clone interaction, where, again, FPS 8 was more responsive to year than other clones.
FPS 6 had the highest average soluble solids and pH values at harvest while FPS 8 had the lowest (Table 3⇓). FPS 4 had the highest TA (7.5 g/L), ~10% higher than FPS 8 (6.9 g/L). The only significant difference in fruit composition between rootstocks was for juice pH, where 110R produced a lower pH by 0.01 pH unit, a viticulturally insignificant difference. Yearly differences were significant for all fruit composition parameters, more likely because of time of sampling rather than a year effect per se.
Average soluble solids data may be somewhat misleading because, in years when crop yields were relatively high (1997 and 2000), FPS 8 lagged behind FPS 4 and FPS 6 in sugar accumulation (Figure 2⇓). However, in years of lower yield, FPS 8 had soluble solids similar to other clones. For example, in 1997 FPS 8 on 110R averaged 16.6 kg/vine and had 20.9 Brix, more than two degrees lower than FPS 6 on 110R that yielded 8.5 kg/vine. By contrast, in 1998 when FPS 8 on 110R averaged 5.5 kg/vine, soluble solids at harvest was 21.9, the as FPS 6 on 110R which had only 1.2 kg/vine (compare Figures 1⇑ and 2⇓).
Titratable acidity was not related to soluble solids or pH. FPS 8 averaged the lowest acidities in each of four data years, regardless of crop load or soluble solids, while FPS 4 had the highest acidity, and FPS 6 was intermediate. Potassium (K) concentration in FPS 8 was much lower than in FPS 4 or 6. Although FPS 4 had significantly lower K concentration than FPS 6, the difference was minor.
Shoot number averaged 26 per vine (11 shoots/m) over the four data years, with a range of 25 to 27 shoots, but was kept consistent among clones in any given year (data not shown). FPS 6 had the highest pruning weight and shoot weight, and FPS 8 the lowest, while FPS 4 had pruning weight about the same as FPS 6 (Table 4⇓). There were no differences between rootstocks in vegetative growth. However, there was a rootstock by clone interaction for both pruning weight and shoot weight. FPS 6 on 5C had consistently higher average pruning weight than FPS 6 on 110R (3.2 kg and 2.8 kg, respectively), while differences between rootstocks grafted to FPS 4 and FPS 8 were slight and inconsistent (data not shown). There were also differences in pruning weight from year to year and was lowest in 1997 and highest in 1998 (Table 4⇓). Pruning weight was negatively related to yield (Figure 3⇓).
The Ravaz index (yield to pruning weight ratio) also varied significantly among clones, but not between root-stocks, and was higher in FPS 8 than in FPS 6 and FPS 4 (Table 4⇑). Ravaz index varied significantly from year to year, and there was a clone by year interaction, reflecting that clones did not respond similarly in different years.
Although Malbec’s historically problematic fruit set in Bordeaux was overcome through clonal selection (Leclair 1995), that is not the case for contemporary Malbec clones in California. In this evaluation, average yield of FPS certified Malbec clones varied four-fold, from a high of 11.4 kg/vine in 1997 to a low of 2.8 in 1998. Yearly variation occurred for all clones (Figure 1⇑) and was largely dependent on berries per cluster (Figure 4⇓). In 1998, average berries per cluster for all clones and rootstocks was 31 berries, less than 25% of the average in 1997 (Table 2⇑). Differences in clusters per shoot were significant (Table 2⇑) and were correlated with yield (Figure 5⇓). This difference should not be interpreted, however, as a clonal difference in numbers of clusters initiated per shoot. In years of low crop and on clones with low crop, clusters that set no berries were observed to desiccate and abscise. Thus, what would be recorded at harvest as low cluster number per shoot would not reflect prebloom cluster number. If there were less than 10 berries per cluster, the cluster would not have been counted at harvest. Comparing prebloom to postbloom cluster counts would be advised for anyone specifically studying cluster number per shoot in clones.
Evaluations of other winegrape variety clones found values of berries per cluster with less yearly variation. In a five-year trial of Merlot clones, average yearly berries per cluster differed about 50%, from 98 to 141 berries per cluster (Benz et al. 2006), and in a three-year study of Pi-not noir clones, average yearly berries per cluster differed only 9%, from 93 to 101 berries per cluster (J. Wolpert, unpublished data, 2001). Malbec FPS 8, although not consistent from year to year, produced enough fruit even in poor crop years to allow for more economic stability. For example, when averaged over both rootstocks, FPS 8 produced 5.5 kg/vine in 1998, the year of lowest yield, when FPS 4 and 6 produced only 1.7 and 1.2 kg/vine, respectively (Figure 1⇑).
Comparing yield and soluble solids data showed that soluble solids level was not dependent on yield when yield was below ~8 kg/vine. Soluble solids of FPS 8 lagged behind FPS 4 and 6 only in high-yielding years of 1997 and 2000 (Figure 2⇑), even though it had the highest yield in every year of the trial (Figure 1⇑).
There was a close inverse relationship between pruning weight and yield (Figure 3⇑), indicating that for clones of low yield, vines responded with higher vegetative growth. The Ravaz index was very low for FPS 4 (2.1) and FPS 6 (1.6), substantially lower than the optimal range of 4.0 to 10.0 (Kliewer and Dokoozlian 2005). Using this criterion, FPS 4 and FPS 6 were undercropped, or, conversely, overly vegetative. This problem is difficult to correct because the small crop was due to few berries per cluster, not a lack of shoot number.
FPS 8 averaged a more balanced Ravaz index of 6.7. However, as the average of four years, this value may be misleading. The index for FPS 8 was 11.3 in 1997, while it was 2.0 in 1998 (data not shown), indicating FPS 8 set too much fruit in high crop years and too little in low crop years. Problems associated with overcropping can likely be corrected through fruit thinning. Poor berry set was shown to be correctable by vineyard practice (Guerra 2006); yield of Malbec FPS 4 on 5C rootstock was increased by shoot-tip removal (“tipping”) at bloom. Yield increase of tipped vines over controls averaged 75%, although that effect was seen only in the second and third years, not in the first year when crop in control vines was high. It is unclear whether FPS 6, with a yield even lower than FPS 4 (Table 2⇑), would also respond with commercially acceptable yield in response to shoot-tip removal. At this time, growers would be better advised to plant the more yield consistent FPS 8 and thin as necessary. Further verification of canopy manipulation to improve berry number per cluster (Guerra 2006), if it is accepted as a standard practice, may lead to planting of clones that are currently problematic.
Malbec has been shown to be more responsive to seasonal influence than other varieties such as Merlot and Pinot noir. Malbec FPS 8 is the only commercially viable clone currently available for planting, although in years of low crop it too can have questionable economic viability. All yield components contributed to the higher yield of FPS 8. The widely planted rootstock 110R had increased yield in high crop years but did not prevent poor fruit set in low crop years.
Acknowledgments: Research funding provided by the American Vineyard Foundation and the USDA Viticulture Consortium.
Establishment of this experiment by Emeritus Professor W. Mark Kliewer is gratefully acknowledged. Authors thank Susan Nelson-Kluk, Foundation Plant Services, UC Davis, for the source information of Malbec clones.
- Received August 2006.
- Revision received February 2007.
- Copyright © 2007 by the American Society for Enology and Viticulture