Evaluating Traits To Improve Grapevine Water-Use Efficiency and Drought Tolerance

The goal of this multi-year project is to identify leaf and root traits that improve drought tolerance and water-use efficiency (WUE) in grape cultivars and rootstocks. Growers will need more drought tolerant and water-efficient vines to avoid declines in berry yield and quality under the hotter, drier conditions expected for California’s wine regions. This project has focused on leaf and root values for the drought tolerance traits the turgor loss point, measured in waterstressed conditions (TLPdry), and the adjustment in turgor loss point between well-watered and water-stressed conditions (DTLP, or TLPwet – TLPdry). TLP measures the water potential threshold that causes cell collapse, which impedes water transport and growth in leaves and roots. A more negative TLP indicates the leaves and roots can undergo more severe water stress before losing turgor. Plants can also change their cellular biochemistry to make TLP more negative under water stress, with a greater adjustment indicated as a larger DTLP. Previous studies found an important role for these traits in drought tolerance in other crops, but these traits have never been assessed for their impact on grapevine performance under water stress.

Our first year, we conducted a greenhouse experiment to evaluate whether rootstocks with a more negative root TLPdry and a larger DTLP allowed vines to maintain greater gas exchange, growth, and WUE under water stress. This year, we have reanalyzed these data and found significant correlations between a more negative TLPdry and larger root system, and between greater vine gas exchange under drought and lower values of a second trait, the root capacitance (CAPdry). CAP measures the volume of water lost from the root as the root dehydrates to TLP. A lower CAP indicates the root loses less volume, with potentially important effects on belowground water transport and root-to-shoot chemical signaling. However, TLPdry was significantly less negative in the rootstocks that field trials have classified as drought tolerant, suggesting that a less negative TLP in dry roots could benefit drought tolerance by redirecting resources to increase root growth in deeper, wetter soil. Together, these findings suggest that root TLP and CAP are promising traits to improve rootstock drought tolerance, though more work is needed to clarify their function.

Our second year, we used a vineyard experiment with 7 wine grape cultivars to test the impacts of leaf TLP and DTLP, and the biochemistry underlying variation in these traits, on scion drought tolerance, including gas exchange, vigor, and berry yield and quality, in realistic vineyard conditions. All 7 cultivars significantly adjusted TLP to improve leaf drought tolerance over the growing season, but cultivar rankings in TLP were highly consistent. However, contrary to expectation, leaf TLP was not related to gas exchange or plant water stress in this study, suggesting leaf biochemistry was responding to other stresses in these vines. Further, this study is the first to report a significant accumulation in mannitol as part of DTLP in wine grapes, which has been shown to ameliorate heat and pathogen stress in other plant species.

Evaluation of Zinfandel Heritage Selections

The 2007 growing season was more moderate, without the heat wave of 2006. The result was far less sunburn in 2007. Harvest was compressed with two harvests only two days apart, Sept 11 and Sept 13. Yield varied from a low of 3.7 kg per vine to a high of 6.6 kg. Regarding yield components, berry wt was a very tight range, differing by only 0.2 g, from 1.5 g to 1.7 g per berry. The yield component clusters per vine, as in previous years, was very close among clones due to crop control via pruning. Cluster wt, also following previous the years? pattern differed widely from a low 174 g to almost 300 g. Given the similarity of berry wt, berries per cluster mirrored the difference patterns of cluster wt, with heavy clusters having the most berries and light clusters the least, a range of 108 to 183 berries. Berry samples for comparing selections were taken on a single date just prior to harvest. It shows a range of 24.1 to 26.6 Brix. Values of pH were very low, as is the usual case for Zinfandel at the Oakville Station, and in a relatively tight range, 3.10 to 3.18. Titratable acidity values were also relatively close, ranging from 7.32 to 8.07 (g/L). The patterns of difference in the 2007 data, are similar to those in the 2005 ? 2007 averages. Ripening was a little more uniform in 2007. Cluster numbers are greater in 2007 but this is due to an increase shoot number over year 2005, and a decrease in sunburn loss over year 2006.

Development of a National Expert System for Diagnosis of Grape Problems

Version 1.0 of the diagnosis expert system has been developed with a database containing information on 161 grape problems including 55 arthropods, 48 pathogenic diseases, 25 phytotoxicity problems, 13 nutritional disorders, 9 abiotic stress disorders, 6 wildlife damage, and 5 physiological disorders. Additional problems will be entered into the database in 2007. The system is currently undergoing debugging and refinement prior to evaluation by a test panel. Production of graphics was initiated in 2006 and draft images have been completed for all first-level menu items.

The diagnosis system uses a symptom-based approach that guides the user through a series of directed questions leading to a ranked list of the most probable problems. The user answers questions based on their observations of symptoms and signs of the problem. Questions are organized in hierarchal levels, enabling the software to analyze responses and select the next level of questions on-the-fly based on the previous responses. This approach streamlines the diagnosis process by focusing on discriminating questions and avoiding extraneous ones.

Each vineyard problem is characterized with diagnostic keywords and a Problem Profile. The system uses the keywords to conduct a sorting routine to identify and display a probability-ranked list of possible problems. The Problem Profile contains text and photographs to assist with diagnosis of the problem.

A database was created to hold Diagnostic Keywords and Problem Profiles for known grape problems caused by pathogens, arthropods, vertebrate and other pests, abiotic stresses, nutritional disorders, chemical phytotoxicity, and physiological disorders. Database entries were created based on the personal experience of the principal investigators and from several standard references including the Compendium of Grape Diseases, 1988 APS Press and Grape Pest Management, 1992, University of California, Division of Agriculture and Natural Resources.

The technical accuracy of database entries will be validated by an editorial review process involving experts from around the U.S. Participation in the project by experts will be facilitated by the previous creation of draft versions of Diagnostic Keywords and Problem Profiles, which will minimize the time commitment of reviewers. Experts will be requested to review and edit selected problems. Reviewers will begin testing version 1.0 of the Expert System in 2007 and will be provided password-protected access to the Problem Profile Editor database interface. Reviewers will be credited for their work and will be invited to contribute new problems based on their experience. High-quality photos of symptoms and signs will also be solicited from experts and photo credits acknowledged. The diagnosis expert system will be validated through test use of version 1.0 and 2.0 by a panel comprised of vineyard managers, Extension educators, and students.

Breeding rootstocks resistant to aggressive root-knot nematodes

The USDA grape rootstock improvement program, based at the Grape Genetics Research Unit, is breeding grape rootstocks resistant to aggressive root-knot nematodes. We define aggressive root-knot nematodes as those which feed on and damage the rootstocks Freedom and Harmony. In 2005 we screened 6201 candidate grape rootstock seedlings for resistance to aggressive root-knot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. These selected seedlings are propagated and then planted into the vineyard. We have 367 nematode resistant selections that will be ready for vineyard planting in spring 2006. In 2005 we planted 38 nematode resistant rootstock selections in the vineyard. These selections were identified in nematode resistance screening in 2004 and 2003. In 2005 we pollinated 857 clusters of crosses specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes.

Development, Testing and Introduction of Grape Rootstocks with Broad and Durable Nematode Resistance

We continue toward our goal of developing and releasing grape rootstocks with broad and durable resistance to nematode species that are important in California vineyards. In previous years, we have screened rootstock candidates against the root-knot nematode (Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the resistance of Harmony rootstock (Meloidogyne arenaria strain A and Meloidogyne incognitastrain C), and the dagger nematode (Xiphinema index). Fourteen rootstock candidates exhibit broad resistance to those nematodes. This year, we continued to test the breadth of that resistance beyond the range of the primary screen species by evaluating the resistance of the 14 candidates to the ring nematode, Mesocriconema xenoplax, in the presence of other nematode species.

We also evaluated ring nematode resistance in the parents of the current rootstock candidates and in some other Vitis sources. Only two of the rootstock candidates exhibit any resistance to the ring nematode and that may not be durable when other nematodes are present. We continue to seek new sources of resistance. We also continued to test the durability of nematode resistance of the rootstock candidates when they are exposed to combinations of nematode species by determining the durability of resistance at different temperatures. Resistance of the parents of the rootstock candidates to several root-knot nematode variants was compromised at soil temperatures of 30°C and above but not below 27°C. However, some of the rootstock parents maintained resistance to even the virulent Meloidogyne arenaria strain A at high temperatures, indicating that there is durability to temperature among the parentage.

Field testing of the rootstock candidates continues in fields that were heavily infested with root-knot nematodes. Nematode population levels are declining in the root-zones of all rootstock candidates, indicating that reproduction of root-knot nematodes is not occurring. However, population levels of ring nematodes at the field site are high on most of the selections, underscoring the need for obtaining new sources of resistance to that nematode.

Evaluation of Zinfandel Heritage Selections

Data were taken for the first time in 2005 on ?Phase 2? of the Zinfandel Heritage Vineyard which is the large, replicated group of 22 clones taken from the Phase 1 vineyard.

Objective(s) and Experiments Conducted to Meet Stated Objective(s):

  1. Viticultural evaluation of Zinfandel Heritage selections
  2. Evaluation of wine made from a select number a Zinfandel Heritage Selections.
  3. Viticultural and enological evaluation of Zinfandel Heritage Selections in the new replicated trial.

Summary of Major Research Accomplishments and Results (by Objective):

In consultation with Zinfandel Advocates and Producers? (ZAP) Research Committee, a decision was made to set aside objectives 1 and 2 in preference to Objective 3. Additional investment in data from the unreplicated vineyard and of small lot fermentations did not make sense in light of the better data and larger wine lots available. Objective involved the viticultural and enological evaluation of Zinfandel Heritage Selections in the new replicated trial.

Twenty-two selections were evaluated for yield components. Yields varied from 2.8 to 6.0 kg/vine. While clusters per vine are somewhat regulated (particularly in young vines relative to vine vigor) they still varied from a low of 14 to a high of 18. The

greatest difference in yield (as is typical for clones) was due to cluster weight, varying about two-fold, from 182 g to 374 g. Berries per cluster varied by about two fold as well, from a low of 89 berries to a high of 181. Berry wt values varied remarkably little from 2.0 to 2.2. Clones were picked on two dates September 9 and September 20. Berry sample Brix at harvest varied from a low of 22.6 to a high of 25.4. An attempt was made to harvest the plots at lower sugar values because of previous years? difficulties completing fermentations in high Brix juices. Values for pH with the Zinfandel at the Oakville Station Vineyards, were low ranging from 3.08 to 3.23 which was consistent with historical values, and TA levels ranged from 6.63 to 7.56.

Wines were made at the Ravenswood winery under the direction of Don Williams and Joel Peterson. Wine data will be available later in the spring. Pruning weight data will be taken later in the winter.

This larger trial will be the source of the most important data from the Heritage Vineyard, as the wine lots will be large enough to give more relevant experience with wines. However, it is too early to place a great deal of value on this data. As vines mature and additional years of data are collected, we will be better able to develop stronger conclusions about the zinfandel selections from the larger replicated trials with greater confidence.

Evaluation of Selected Mediterranean Wine Grape Cultivars and Clones in Lake and Mendocino Counties

During the year 2000, phenological and harvest data were taken from three Mediterranean Winegrape Cultivar Test Plots in Lake and Mendocino Counties. Results indicate that there are tremendous differences in budbreak, yield and harvest dates between the cultivars and locations.

In Lake County, all cultivars reached ripeness (23.5 brix) in the Red Hills plot, whereas only the earliest cultivars reached ripeness in the Highland Springs plot. This can be explained partially by the warmer climate of Red Hills, but also by the smaller crop size and lighter soils in that plot compared to larger crops and heavier, cooler soils found in Highland Springs. In general, the ripening sequence is as follows: Pinotage, Barbera, Dolcetto, Grenache, Nebbiolo, Cabernet sauvignon, Sangiovese, Cinsault, Syrah,. Harvest occurred from Sept.15, to Oct. 27th, 2000. At Highland Springs, only Pinotage fully ripened during the 2000 harvest.

At the UC Hopland Research and Extension Center, there is a greater number of cultivars being tested. Ripening sequence this year was Pinot gris, Viognier, Tempranillo, Cinsault, Grenache, Syrah, Sangiovese, Dolcetto, Viognier (?Bonny Doon? clone), Fiano, Freisa, Mourvedre, Nebbiolo, Corvina, and Aglianico. Canailo nero, Montepulciano and Marsanne failed to adequately ripen, and were lost due to rain damage. A research progress report of the UC HREC data is being prepared for a California Agriculture magazine issue featuring the 50th anniversary of the UC Hopland Research and Extension Center.

In nearly all cases, quality of the fruit was quite high, showing adequate sugar (23.5 brix), good acidity, and very little rot. For the combined trials, 22 lots of wine are being fermented. It is clear that there are many cultivar options for quality winemaking in Lake and Mendocino Counties.

We were not able to plant a clonal trial of Syrah during this season. Vines will be planted in 2001. Evaluations of 5 Syrah clones were made from commercial plantings at McDowell Valley Vineyards. Clones include Syrah noir (?Hermitage? clone), Shiraz (UC clone #1), McDowell clone, CTPS #877, and CTPS #174. Significant differences in cluster size, shape and yield per vines were noted, as well as must chemistry. Separate lots of wine were vinified, and there are definite organoleptic differences between the clones. While not statistically valid, these observations are still helpful in assessing differences between the Syrah clones. Information from this survey will be presented at the ASEV Syrah Symposium in San Diego in June, 2001.

PDF: Evaluation of Selected Mediterranean Wine Grape Cultivars and Clones in Lake and Mendocino Counties

Evaluation of Wine Grape Cultivars and Selections for a Cool Maritime Climate

The primary trial was established in 2000 at two vineyard plots, one located at Mount Vernon research station and one located with Louis Dailly at his vineyard near Concrete. A randomized block of 3 replications, with 5 plants per replication has been established. At the station site, plot size is 10′ rows with 6′ between plants, total area of the planting approximately 0.5 acre. The upriver plot is planted at 8′ rows with 6′ between plants. In addition, a preliminary evaluation, consisting of three plants per variety in two rows at each location, has been established to test certain other varieties/selections which can be added to the primary trial later if their performance warrants inclusion. A rootstock trial of Pinot Noir 2A has been planted in both locations, consisting of seven rootstocks plus self rooted plants, to test for earlier ripening potential. This trial includes five plants of Pinot Noir 2A on each rootstock, replicated three times, established at each plot location. Plants rooted in 1999 were planted in spring 2000. Irrigation lines, posts and wires have been installed and training vines will begin in spring 2001.

PDF: Evaluation of Wine Grape Cultivars and Selections for a Cool Maritime Climate

Evaluation of Winegrape Clones

This project evaluates 20 Pinot noir and 13 Chardonnay clones for their viticultural and enological attributes in production of base wines for sparkling wine production and five Merlot and three Malbec clones for their viticultural and enological attributes for production of red wine. Replicated plots of Pinot noir and Chardonnay clones have been established at Gloria Ferrer in Sonoma and of Merlot and Malbec at the Department?s Oakville Experimental Vineyard.

Chardonnay mean harvest °Brix was 21.6 in 2000 and did not vary by more than 0.6 °Brix from the mean with the exception of the Wente clone that was harvested 1.2 °Brix above the mean. This compares with the three-year average that shows a mean harvest Brix of 20.8. The yield range was approximately 2x for the three-year data and in 2000. In 2000 clone 4 had a yield of 8.2 kg vine-1 and the Wente clone yield was 4.0 kg vine-1. For the majority of Chardonnay clones harvest date was correlated to vine yield with two notable exceptions. While clone 4 has the largest crop and latest harvest date, the harvest date appears to be delayed more than the yield would warrant when compared to the other clones. Likewise, the Wente clone with the lowest yield also has a much later harvest date than we would predict. These observations hold for both the 2000 and three-year data.

Mean Pinot noir harvest °Brix for 2000 was 19.9. Harvest was completed over a 21-day period in 2000 and the two-year data shows a 19-day span. In both instances clone 4 was the first harvested and clone 780 the last. Yield ranged from 5.7 (clone 870) to 9.4 (clone 666) kg vine-1 in 2000.

As in preceding years, Merlot clone FPMS 8 had the lowest yield (6.3 tons/acre) in the 2000 growing season compared to the other clones (9.2 to 10.3 tons/acre). The primary contributing yield component was berries per cluster (103 for clone FPMS 8 versus 151 to 164 for clones 1, 3, 6, 9) this was also consistent with past data. In 2000 clone FPMS 8 produced the smallest berries and second lowest number of clusters per shoot. Averaged over six years, clone FPMS 8 has produced approximately two thirds the yield of the other four clones due to smaller clusters caused by reductions in both number of berries per cluster and berry size.

Mean yield for all Malbec clones was 4.9 tons/acre for the 2000 crop and was 40%above the average of the preceding 4 years (3.5 tons/acre). Clonal differences were evident in all components of yield except berry weight. In 2000, clone FPMS 08 was again the most fruitful in all components and produced 9.7 tons per acre compared to 4.1 and 2.2 tons per acre for FPMS 04 and 06. In each of the last four years, FPMS 08 has consistently produced the greatest crop and FPMS 06 has produced the least. Averaged over five years, yields were 3.0, 2.2, and 6.2 tons per acre for FPMS 04, 06, and 08 respectively.

PDF: Evaluation of Winegrape Clones

Clonal Testing of Wine Grapes in the San Joaquin Valley

This is an ongoing study to evaluate promising, virus disease-free FPMS clonal material for the San Joaquin Valley. Completion dates for past trials were: French Colombard and Chenin blanc (1994), Barbera (1995), and Muscat of Alexandria (1997), Grenache (1998), and Muscat blanc (1998). The Sangiovese trial was completed in 1999 with crop level comparisons. Data collection continued (2nd fruiting year in 2000) with the Chardonnay, Cabernet Sauvignon, Merlot, and Zinfandel/Primitivo trials. These trials were planted with 6 clones each in 1997 in order to evaluate clonal differences in a warm climate region. A new Barbera trial was planted in 2000.

Cabernet Sauvignon. Clones 2 and 24 again produced smaller berries and clusters than the others, as in 1999. This corresponded with lower yields and earlier fruit maturation. These characteristics tend to be more prevalent in Clone 2. The other clones ? 8, 10 ,21 and 22 ? were all similar.

Merlot. The Merlot clones showed significant differences in fruitfulness, berry weight, total vine yields, and fruit composition. Mostly, the differences were small. Some noteworthy responses included: heavier berries of lower pH in Clone 11; and lower vine yields from Clone 14 due to fewer clusters and smaller berries than some of the others. In contrast, Clone 10 produced 40%more yield than Clone 14 and with similar berry weight and fruit composition. Overall, Clone 10 performed very well, similar to Clones 3 and 9, except that it also produced smaller berries.

Zinfandel/Primitivo. Clonal differences were not as distinct as they were in 1999 when the Primitivo clones had smaller berries, fewer berries/cluster and clusters of lower mass and earlier ripening and less rot as compared to the Zinfandel clones. The Primitivo clone vine yields also tended to lower than those of Zinfandel in 1999. In contrast, the Primitivo clones tended to produced higher harvestable yields than those of Zinfandel in 2000, possibly due to less rot per cluster. Fruit soluble solids were higher in P3 and P6 as compared to 1A and 3. This is similar to the 1999 data showing earlier fruit maturation in the Primitivo clones as compared to Zinfandel. Titratable acidity was also higher in several of the Primitivo clones (P5 and P6) as compared to Zinfandel 2 and 3. Overall, clonal differences within the Zinfandel and Primitivo clone groups were small; they were greater between the two groups.

Chardonnay. Significant clonal differences were again measured in 2000, but the data is too preliminary to demonstrate important or consistent effects. For example, Clone 4 of outstanding performance in 1999, was of lower yield in 2000, the result of fewer clusters per vine. Vine yields were highest with Clones 15, 18, and 20 and lowest with Clones 4, 6, and 37. Yield differences could be largely attributed to differences in clusters/vine and/or cluster weight. Fruit maturation was largely influenced by total fruit weight. Clone 20 again produced the heaviest berries while Clone 6 produced the lightest clusters. The 2000 results of these trials are preliminary. They represent two years of data collection, the first of which was the 3rd leaf vine data in 1999.

PDF: Clonal Testing of Wine Grapes in the San Joaquin Valley