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.

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.

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.

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

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