http://www.avf.org/results.html

ENOLOGY

 

Identification of Factors that Influence the Level of Large and Small Polymeric Pigments in Grapes and Wines

Principal Investigator: Douglas O. Adams

We have identified many of the important fermentation parameters that influence tannin extractions and polymeric pigment formation. Among the factors we studied, temperature seems to play the largest role. We have observed important compositional changes that occur in wines as they age and have provided the industry with the tools to quantify those compositional changes with a simple inexpensive assay for tannins and polymeric pigments.

We have shown that polymeric pigments bleach with SO2 and have conducted experiments to measure the degree to which they bleach. This research has provided vintners/growers with information that can be used to derive much more accurate values for wine pigments, especially the polymeric pigments which are responsible for permanent color in red wines.

 

Identification of Yeast Strain Genetic Factors in the Formation of Volatile Sulfur Compounds

Principal Investigator: Linda F. Bisson

Benefits to the industry. First, we have a better understanding of strain variability under production conditions. If the nitrogen requirements and biochemical characteristics of a strain are known, then nitrogen supplementation can be used effectively to reduce the incidence of volatile sulfur. However, this information is not trivially gotten. Second, supplementation with specific amino acids (methionine and cysteine) will not be generally effective and are strain specific. High threonine content relative to methionine should be avoided. Further, imbalances in sulfur containing amino acids in the juice could lead to the formation of complex volatile sulfur compounds that are the degradation products of these amino acids. We recommend against indiscriminant supplementation with sulfur containing amino acids. Strain response to increases in fermentation rate, changes in temperature, and stress with respect to H2S formation are variable. Analysis of each strain must occur, as general principles predicting the behavior of all strains do not exist unless the genetic background of the strain has been fully characterized. Finally, one of our additional goals was to determine the best method for the construction of strains with reduced H2S production. Mutational decreases in specific enzymes of the sulfate reduction pathway, such as via the elimination of sulfite reductase, led to more problems than they solved. Dramatically higher sulfite production occurred. Further, increases in levels of enzymes that had been shown to reduce hydrogen sulfide in brewing strains were of limited effect. Over-expression of some is toxic and therefore not a viable means to generate commercial strains. Analysis of the one strain that was a low producer under all conditions tested indicated that it carries a specific mutation in an important regulatory region of the CYS4 protein allowing high Cys4p activity and maintenance of high cysteine pools under conditions of stress. Our next grant in this area will focus on this gene and the possible use of this naturally occurring allele to reduce sulfide production across a wide spectrum of strains.

 

Analysis of Saccharomyces during Normal and Problem Fermentations

Principal Investigators: Linda F. Bisson, et al.

The aims of the first three years of this proposal were to acquire, develop and optimize technologies for the analysis of problem fermentations. The goal of this work is to develop better fermentation management strategies to reduce and hopefully eliminate the incidence of slow and incomplete fermentations. In this first phase of the research we have successfully adapted functional genomic analysis to Saccharomyces grown under enological conditions. We have identified several key differences in the physiology of yeast grown under nutrient sufficient versus nitrogen-limited conditions. We have begun identifying molecular markers associated with healthy or robust fermentations and those associated with nutritional or environmental stress. The project is well poised to complete this analysis in the next year and to identify key yeast strain and physiological input factors needed for full optimization of the predictive potential of neural networks. We have developed bacterial-specific primers for direct analysis of bacterial strains in wine. In addition, we have developed and tested several yeast specific primers and employed them on samples obtained from commercial wine fermentations. This approach has resulted in direct identification of viable but non-culturable yeast populations, a potential factor in stuck fermentations. The project is well poised to complete this analysis in the next year and to identify key yeast strain and physiological input factors needed for prediction of fermentation kinetics. In addition to the molecular and physiological work, we are currently completing detailed analysis of samples from over 200 commercial Chardonnay fermentations from the 2001 harvest. Analysis of the juice and wine from these fermentations, which ranged from normal to sluggish and stuck, will allow us to identify juice characteristics and processing choices that are critical in determining fermentation kinetics. We have also developed bacterial-specific primers for direct analysis of bacterial strains in wine. In addition, we have developed and tested several yeast specific primers and employed them on samples obtained from commercial wine fermentations. This approach has resulted in direct identification of viable but non-culturable yeast populations, a potential factor in stuck fermentations. With all yeast physiological and microbial ecology factors, juice characteristics, and processing parameters identified that are critical in determining wine fermentation kinetics, we will be able to predict problem fermentations and their resolution early in the fermentation process.

 

Evaluation of the Influence of Common Viticultural Practices on the Chemical and Sensory Characteristics of Wines

Principal Investigator: David E. Block

Carrying through viticultural trials to winemaking is a natural extension that should maximize the useful information arising from these studies. Knowing which viticultural practices are important in determining wine characteristics will allow winemakers and vineyard managers to specify how a vineyard might be managed in order to achieve certain sensory or chemical goals for the finished product. In addition, a winemaker could use information on the viticultural practices used to produce a lot of grapes to modify enological practices in order to limit or enhance these effects.

 

Kinetics of Flavor Formation During Grape Juice Fermentations

Principal Investigator: Susan E. Ebeler

This work is providing information about the dynamic changes that occur in flavor production through out grape juice fermentations. By identifying important variables that may influence ester formation (e.g., fermentation rate, yeast species and inoculation rate, fermentation temperature, etc.) we will ultimately be able to provide winemakers with information and tools that they can use during the winemaking process in order to optimize and control the flavor of the final wine.

 

Vegetative Aroma: Sensory Definition, Chemical Interpretation (and ultimately) Causal Explanation

Principal Investigators: Susan E. Ebeler, David E. Block, Ann C. Noble, and Nick Dokoozlian

This research is still in preliminary stages. When completed this work will provide an improved understanding of vegetative aromas in Cabernet Sauvignon wines, including a qualitative and quantitative assessment of the sensory perception of vegetative aromas, identification of chemical components which may contribute to vegetative aromas, and a characterization of viticultural and/or enological parameters which can influence development of vegetative aromas in grapes and wines.

 

Investigation of Factors Influencing Perception of Astringency

Principal Investigator: Ann Noble

Over the last 5 years, we have made considerable progress at understanding how astringency is perceived. We have confirmed that people with higher flow astringency perceive it less intensely than low flow people, which does not provide information for marketing but contributes to our understanding of perception of astringency. As is typical in scientific research, each new discovery raises new questions. The fact that artificial saliva with 3 g/L protein did not reduce astringency below that perceived when the artificial saliva had NO protein is puzzling. Perhaps no significant difference occurred because with low-flow we didn’t introduce enough protein, whereas at high-flow the dilution effect is overriding. Further work remains to understand what astringency is and how we perceive it.

For routine tests in a winery or at competitions, rinsing with a pectin solution (4 to 5 g/L) between wines should greatly increase the reliability of the tasting. As demonstrated in our work, use of a pectin rinse can reduce the carryover of astringency, which permits the tasting of many wines at a session without having an enormous difference occur over time where each subsequent wine is perceived as more intense just because of the cumulative effect of carry-over.

 

Tannin Development in Grape Seeds

Principal Investigator: Andrew Waterhouse

In order to validate the oxidation hypothesis of tannin development, and address our goal: Measure the presence of oxidized tannins in seeds, we are investigating methods to directly measure the initial oxidation produce of phenols, quinones. One method using a redox titration did not yield any oxidation product, and an attempt to directly observe quinones by NMR spectroscopy did not show any quinones present. The lack of response may be due to the low sensitivity of these two methods, so a third, and much more sensitive method is now being tested. It involves the production of a reaction product, phenazine, which is totally specific for the presence of ortho-phenols, the expected phenol in seed tannins. We are synthesizing a standard phenazine and will apply this method to testing for quinones in tannins. This method should be simple enough to apply in winery laboratories.

The Chemical Evolution and Preservation of Color in Red Wine Aging

Principal Investigator: Andrew Waterhouse

The preparation of labeled Malvidin-3-glucoside was successful using an enzymatic preparation and the procedure has just been published in the Journal of Agricultural and Environmental Chemistry. This valuable tool has now been employed in a study of the fate of anthocyanins in the aging of new wine. We expect results in this wine experiment over the next year.

 

VITICULTURE

 

Developing a Functional Genomics Approach to Berry Ripening and Defense

Principal Investigator: Douglas O. Adams

Wine quality is largely determined by fruit composition at harvest. Grape variety, environment, soils, weather and cultural practices should be viewed as a biological continuum where the environment influences gene expression, which in turn determines the characteristics of the biosynthetic processes that ultimately determine fruit composition. Therefore, if we have any hope of understanding how the environment influences fruit composition we must determine what genes are expressed at a given time in berry development. We must also know what tissues those genes are expressed in. This project has already provided some of the tools needed to begin to address these biochemical and physiological issues.

The timing and level of expression of grape genes determine the quantity and nature of grape berry components. This research has continued to provide new tools to study fruit development and ripening. This project has identified and isolated several genes associated with disease resistance that can be used immediately in the search for an early molecular marker of the vine’s response to Pierces Disease. We have identified several genes that are candidates for fruit specific expression under normal conditions. This work will have general applicability in the study of grapevine biology, and with the tools available from projects such as this, the response time required to address new problems can be shortened perhaps by years.

 

Clonal Testing of Wine Grapes in the San Joaquin Valley

Principal Investigator: Peter Christensen, Extension Viticulturist, Emeritus

This research has already provided the grape industry with clone performance information and recommendations for important warm climate cultivars -- French Colombard, Chenin blanc, Barbera, Muscat of Alexandria, Muscat blanc, Grenache, and Sangiovese. The trials are the first and only to be conducted on these cultivars in California with the exception of Sangiovese. The data have assisted nurseries, growers and vintners in selecting the best performing clones and to avoid clones with inferior or undesirable characteristics. Examples include the recommendation to use Chenin blanc Clone 4 or Clone 1 and to avoid Clone 5, which produces very tight clusters with a 75% higher bunch rot level than the others. Future Muscat blanc plantings should use Clone 4 from Milan and avoid the widely planted Clone 1 with its lower fruitfulness of heavy, rot-prone, and larger-berried clusters. Grenache growers can choose between Clone 1A with high cluster numbers, smaller berries, and less rot potential or Clone 3 for higher yield, although with heavier clusters and berries, some delayed fruit maturation and a greater rot potential. Sangiovese Clone 4 should be avoided in warm districts due to poor fruit composition (low TA and high pH), high bunch rot incidence and lower anthocyanin content in the wine; Clone 2 is more fruitful and of smaller berry size than Clone 3. Other cultivar clonal preferences from this research include Muscat of Alexandria Clone 2A, French Colombard Clone 2 and Barbera Clone 6.

The data from the Chardonnay, Cabernet Sauvignon, Merlot and Zinfandel/Primitivo are showing significant differences among many of the clones after 2 years of full production. The information will be of long-term importance to growers and wineries interested in growing these cultivars in warm regions. The continuation of clonal evaluation of the new Barbera clones from Torino and the reintroduction of FPMS Barbera Clone 6 (previously Clone 1) will be important to future plantings of this cultivar. The only registered Barbera in previous years was Clone 2, shown in our trials to have heavy berries and clusters of lower anthocyanin content and a high bunch rot potential.

 

Cultural Practices for Integrating Arthropod Pest Management with Improvements in Grape and Wine Quality

Principal Investigator: Michael J. Costello

The information that we find in this study has enormous implications for the grape and wine industry. Cultural practices to improve wine quality is high on the list of priorities within the viticulture industry, and finding non-chemical approaches to insect pest management is also highly desirable within the industry. We believe that we have begun to help fill some of the need for information on these two vital topics.

 

Enhancement of Stress Tolerance in Vitis vinifera

Principal Investigators: Grant R. Cramer and John C. Cushman

Much of the first half of the year was directed at exposing plants to stress treatments, collecting organ samples and extracting RNA from those samples. Mixed stress cDNA libraries for berries and leaves have been made and EST sequencing has begun. Raw sequences were analyzed in cooperation with Jennifer Weller at VBI. Approximately 36% of the sequences are novel and sequence redundancy is low. All unique sequences identified to date have been deposited in GenBank (accession no. BM436250 – BM438127) and are available to the public at the NCBI website: http://www.ncbi.nlm.nih.gov/dbEST/index.html

This grant has acted as seed money for the development of a much larger research initiative to conduct an integrative functional genomics project on abiotic stress and wine characteristics. The initiative includes an integration of genomic, proteomic and metabolomic approaches. It also expands research to Cabernet Sauvignon. Two multi-institutional grants have been submitted to IFAFS and the NSF Plant Genome program, respectively. The IFAFS grant, submitted in April 2001, was not funded and that program will not be accepting new proposals in 2002. The NSF grant was just submitted in January 2002 and is still pending.

The International Steering Committee for Grape Genomics is in the process of developing a white paper that describes the current and future status for grape genomics on an international scale. We are active participants in the ESTs and transcriptional profiling, and Bioinformatics working groups and hope to play a supportive role in the development of a community database for EST information and DNA microarray gene expression data in collaboration with the Virginia Bioinformatics Institute. We have established an automated EST analysis pipeline (ESTAP) and associated database that could serve as the main repository for EST sequence information (and related gene expression information) for projects in the public domain and information released publicly by privately funded gene discovery projects. The grape EST database we have created can be easily expanded to serve as the foundation for a public database for the International Grape Genomics community. This database will be integrated with the web-based information portal established at UC Davis (see http://grapegenomics.ucdavis.edu/main.cfm) by Dr. Doug Cook. This site contains a database of researchers, resources for grape genomics, and links to other relevant sites.

Ultimately, the data sets obtained from this research will contribute to a reliable prediction model for wine characteristics. This research will greatly facilitate future gene discovery and enable improvements to be made in both production efficiency and wine quality under environmentally adverse growing conditions.

 

Investigation of Grape Mealybug Population Dynamics to Forecast and Prevent Outbreaks and Improve Control

Principal Investigator: Kent M. Daane

The development of least toxic controls for mealybugs in the grape mealybug complex were not fully addressed until this research. We began work with a description of seasonal mealybug age structure and seasonal development, which has resulted in the production of guidelines for more rapid sampling. During the past two years we switched our focus to control programs, investigating both biological and cultural control. Our work clearly showed the importance of ant control in the establishment of effective biological controls. This led to ongoing collaborative projects with Dr. Mike Rust and Dr. John Klotz to develop better ant control programs for vineyards. A 25% sugar solution and small amounts (0.001-0.0001%) of either imidacloprid, fipronil or thiomethoxam were placed in bait traps throughout a heavily infested Napa Valley wine grape vineyard. Results show a significant late-season reduction of ant activity at the fipronil and thiomethoxam treatments. However, there was no reduction in mealybug density or increase in parasitoid activity. While results showed no economic reduction of Argentine ants, we are encouraged by new information gained and will make the needed adjustments for study in the 2002 season. We also have developed insectary rearing methods for some of the more important mealybug parasitoids. Currently we are testing the augmentative release of one of those parasitoids: Pseudaphycus angelicus. Finally, we have carefully studied the effects nitrogen fertilization (0, 25, 50, 100, 200 and 400 lbs/ac) and girdling and gibberellic acid practices on mealybug populations. Results from field trials showed no difference between N fertilization treatments or berry sizing practices in mealybug density or egg deposition. We believe these field results were influenced by resident natural enemies, which lowered mealybug densities. In controlled greenhouse trials, mealybug densities and egg deposition on potted plants were greater in higher N fertilization treatments. We conclude that more vigorously growing vines can increase mealybug pest status. The effect of cultural practices have always been questioned by growers and now some of these questions have been answered.

 

Influence of Row Orientation and Canopy Density on the Microclimate and Composition of Cabernet Sauvignon Grapes

Principal Investigator: Nick Dokoozlian

The effects of row orientation and cluster exposure to sunlight on the fruit zone microclimate and fruit composition of Cabernet Sauvignon were studied in a commercial vineyard in the Napa Valley. We found that row orientation had a significant effect on fruit zone microclimate. South and west exposures intercepted more sunlight than the opposing exposures, resulting in greater daytime berry temperatures. The most exposed fruit on south and west exposures intercepted two to three times more light, and accumulated more than six times the thermal energy, compared to fruit from east and north exposures. Fruit from north-south row orientations accumulated more heat than fruit on east-west orientations on a daily basis. However, fruit located on the canopy exterior on west and south exposures exhibited reductions in skin phenolics and anthocyanins, and were subject to physical damage from excessive temperatures, when compared to moderately exposed fruit. Fruit from the exterior exposures produced wines of lower color and malic acid levels, and disproportionately contributed to variation in fruit quality from the vineyard as a whole. The results indicated that row orientation has specific and predictable influence on fruit composition based on variations in the fruit zone microclimate, and that row orientation influences the level of fruit damage from exposure to high light and high temperature. Sunlight levels of 150 m mol·m-2·s-1 to 400 m mol·m-2·s-1 at mid-day were ideal for optimizing fruit composition. These light levels correspond to fruit within the canopy interior covered by approximately one leaf layer. The study also suggests that the optimum row orientation in the Napa Valley is northeast-southwest. This orientation moderates differences in fruit exposure between the two sides of the canopy, as well as reduces the duration of high exposure for clusters located on the canopy exterior. Results of the study have been presented at local and statewide industry meetings, the Unified Meeting in 2002, as well as the Annual Meeting of the American Society for Enology and Viticulture in 2001. The study will be completed following harvest in 2002.

 

Wine Grape Trellising and Vine Spacing Studies

Principal Investigator: Nick Dokoozlian

This study provides a detailed comparison of the six modern trellis systems (Sprawl, VSP, Wye, Lyre, Smart-Dyson and Smart-Henry) used for wine grape production in California, as well as basic information regarding the effects of in-row spacing on the productivity and canopy characteristics of several common training/trellis systems used in the San Joaquin Valley. The primary goal of this work was to develop fundamental information to improve the efficiency of both vineyard design and management. Toward this goal, the relationship between trellis type and canopy size has been illustrated for the major systems used in California. We found that canopy density across all systems was best described as leaf area per canopy volume (m2m-3), and this expression has been incorporated into subsequent work. The expression has also been correlated with vine yield components and fruit and wine composition data, providing an integrated picture of how trellis type and vine vigor potentially interact on light microclimate and vine performance. The study also examined the effects of in-row spacing on the productivity and canopy characteristics of several commonly used trellis systems. The data illustrated the impact of in-row spacing on canopy density, light microclimate, vine productivity and fruit and wine composition. Both portions of the study (trellis and vine spacing) provide fundamental information on how to improve the efficiency of vineyard design by optimizing trellis selection and in-row spacing based an anticipated vine vigor. Results of the study have been presented at local and statewide industry meetings, the Unified Meeting in 2000 and 2002, as well as the Annual Meeting of the American Society for Enology and Viticulture in 2000, 2001 and 2002. The study will be completed following harvest in 2002.

 

 

Development of Grape Rootstocks with Broad and Durable Nematode Resistance

Principal Investigators: Howard Ferris and M. Andrew Walker

Crosses made among a series of Vitis and Muscadinia species have resulted in selection of candidate rootstocks with multiple nematode resistance. Some rootstock candidates have now progressed to field trials for tests of horticultural characteristics and to assess the durability of the resistance against field populations of nematodes in a range of environments. We need to continue testing of durability of the resistance when plants are exposed to other nematode species. We also need to determine whether the broad resistance identified in 14 genotypes is effective against other nematodes not yet tested.

 

Effect of Partial Rootzone Drying on Vine Water Relation, Vegetative Growth, Mineral Nutrition, Yield Components, Fruit Composition, and Wine Quality in Sauvignon Blanc Grapevines

Principal Investigator: Sanliang Gu

This research evaluated the feasibility of PRD as a useful vineyard irrigation practice for wine grape production areas with dry growing season such as the San Joaquin Valley of California and separated the effect of reduced irrigation rate from switching the wetting and drying sides. It was demonstrated that the observed benefit such as saving irrigation water, increasing water use efficiency, and controlling vine vigor while maintaining crop yield is mainly originated from the reduced irrigation rate, not from switching the wetting and drying side. It seemed possible to achieve similar vine vigor, canopy characteristics, yield components, fruit composition, and wine quality by managing irrigation at a reduced amount of irrigation water without switching the wetting and drying sides using PRD.

 

Study of the Endophytic Nature of Phaeoacremonium and Phaeomoniella spp. in Grapevines

Principal Investigator: Doug Gubler

Understanding the biology of pathogens is critical to development of control strategies. In this project we have determined that stress factors play an important role in the apparent triggering of the increase in virulence of Phaeoacremonium spp. and Phaeomoniella chlamydospora. Inoculated and control vines were placed in a vineyard at UC Davis in such a way that the roots were artificially "J"-rooted. By the end of the season (2002) the vines that were poorly planted had developed about 50% of the growth of control vines, ie not "J"-rooted. Inoculation with either group of pathogens made little difference in growth. However, we will not destroy the vines to look for internal discoloration until the end of 2003 so we can not make a statement re movement of the pathogens in the wood. Other stresses being investigated are water deficit stress which also showed similar stunting and death of plants whether inoculated or not and fruit load stress. The latter trials are established in commercial vineyards and 2002 will be the first year of fruiting on 2nd leaf plants. Fruit will not be allowed to set on some of the plants until 2003 and 2004. No results are available for this portion of the study.

Another part of this study deals with chemistry of the sap as a potential differential triggering mechanism for "turning on" the pathogens causing Petri disease and black measles. We have demonstrated that when sap constituents are analyzed between water stressed and non-water stressed plants, there appears dramatic differences in the proteins occurring there. In healthy growing plants the proteins are abundant whereas in water stressed plants the bands are greatly reduced. We still don't know what the proteins are but work is in progress to identify these compounds. We suspect that as with other endophytic pathogens, that stress will cause the suppression of important compounds that in turn will allow faster more stable growth of the pathogens.

Evaluation of Sierra Foothill Zinfandel Selections

Principal Investigator: Donna Hirschfelt

This research will provide Sierra Foothill and other grape growers with essential information on the performance of different selections of Zinfandel. Wood is currently in demand, being propagated and sold from many of these selections, despite their virus status. They are selected primarily on historic value and on performance in their original site on their own roots. It is critical to evaluate their performance on rootstock in a single site. This trial will provide valuable information on the virus status of these materials and the impact of virus on fruit quality.

Development of Trapping Systems to Trap the Glassy-winged Sharpshooter Homalodisca Coagulata Adults and Nymphs in Grape

Principal Investigator: Raymond L. Hix

Improved vector monitoring and development of alternative trapping methods are one of the areas of concern for the Glassy-winged Sharpshooter (GWSS), Homalodisca coagulata, and the Diseases They Vector DANR Workgroup. The current trap being deployed by PCA’s, California Department of Food and Agriculture, and United States Department of Agriculture for monitoring GWSS populations throughout California is the Pherocon AM trap and its clones designed about thirty years ago for the apple maggot, hence ‘AM’ designation. The reliability of that trap is questionable, especially at low populations. Furthermore, the relationships between trap catch and grape or citrus canopy populations are unknown.

Research for trap improvement and development for GWSS monitoring is addressing the following: 1) which hue of yellow is the most attractive to GWSS; 2) the field longevities of a trap before weather and photo degradation impact trap reliability; 3) relationships of trap catch to populations of GSS in citrus and grape; 4) the wave length of both emitted and reflected light to which GSS responds (i.e., spectral sensitivity).

We have a yellow trap that consistently catches more GWSS at high populations than does the ‘AM’ trap; it is also more reliable than the ‘AM’ trap at low populations. We also have an orange trap that is as reliable as the ‘AM’ trap at high and low populations. While the yellow prototypes catch significantly more GWSS overall, the interesting thing is that the orange prototypes catch about as many ovipositional GWSS females as yellow prototypes. While yellow is clearly the best choice for trap color, a more reliable trap design than the ‘AM’ trap is feasible. One approach would be to modify existing sticky cards from the various manufacturers to eliminate reflectance below 500 nm and apply a stickier glue to the cards. Other improvements may come from shape and dimension modification. Alternatively, a new trap could be created from scratch incorporating all of the positive features from experimental and existing traps in regards to catching GWSS.

We now know that GWSS females with white forewing spots are mated and ovipositional. These wing spots consist of rod-shaped brochosomes, which are only produced by mated females. These brochosomes are scraped onto the egg masses during oviposition. This information provides us with a link to trap catches and oviposition in associated vegetation. The interesting thing is that while the yellow prototypes caught two to three times as many GWSS as the orange prototypes, the orange prototypes caught as many females with white forewing spots consisting of rod-shaped brochosomes.

Current work is being done to determine ways to enhance the trapping day length. The current optimum trapping period is about three hours per day. This will increase our chances of detecting GWSS at low populations.

Biological, Cultural, Genetic, and Chemical Control of Pierce’s Disease

Principal Investigator: Bruce Kirkpatrick, et al.

Use of riparian vegetation management for controlling Pierce’s Disease in North Coast California vineyards may effectively decrease local populations of the pathogen, Xylella fastidiosa, and its vector, the blue-green sharpshooter. This research will improve our understanding of the roles riparian plant species have in the spread of Pierce's disease, which will allow growers to maximize the efficacy of riparian vegetation management for disease control and minimize negative impacts on important riparian habitat for native plants and wildlife.

Pierce’s Disease is currently the major threat to Vitis production in California. Our research has documented that variations in xylem fluid chemistry affect the growth habits of Xylella colonies, and that high variability in xylem fluid chemistry exists between Vitis genotypes and also with time of year. We have shown that even short-term exposure of Xf to xylem constituents alters Xylella growth, and our development of a simplified media for Xf culturing now allows us to identify the role of specific xylem constituents in Xylella colony formation. Understanding of the role of xylem nutrients to Xf growth can be used as a management tool, as we have established that cultural conditions can be used to alter xylem chemistry. Xylem composition may also be used for selection criteria in genotype choice. We have also identified and quantified the antimicrobial effects of naturally occurring compounds (lytic peptides) that may be incorporated into Xf control strategies.

Symptom evaluation data from the 8-year-old Merlot vineyard in Napa suggests that the most effective mode of treatment delivery is to directly inject the materials in a gel-like matrix into the vines cordon. Foliar treatments must first be taken into the plant to become systemic, and the concentration of material that actually makes it into the xylem is going to be much lower than the concentration at the plant surface. D.P. screws place the treatments within the xylem, but only a small area of exposure is produced and materials must be taken up by xylem passing through the cotton pellet. Drill/injection seems to result in a more efficient uptake, possibly due to the increase in xylem surface area exposure created by drilling completely through the vine. The agarose matrix also creates a continuous bridge for xylem passing from below the application site to plant parts above. The difference in efficacy between Streptomycin applied as a DP screw and as a drill/injection further strengthens this argument.

Micronutrients (zinc, manganese, and copper) applied as direct injections and at higher rates than labeled for micronutrient deficiencies appear to have the potential of creating an unfavorable environment for Xf. This is evident in the 8-year-old Merlot vineyard in Napa where these micronutrients produced disease ratings up to 50% lower than ratings recorded for untreated controls when applied as a direct injection.

Severe pruning continues to give initial positive growth response in the summer after the vine is severely pruned in the preceding winter. The low disease ratings recorded in the fall 2001 for 6-year-old Merlot vines in Napa pruned in February of that year coincide with similar results recorded during the fall of 2000 for 8-year-old vines pruned early in the 2000 season. Pruning a cordon to within 6 to 8-in. of the graft union allows a previously infected vine to send up a new shoot that will be trained into a cordon that is free of xylem blockage. Ideally, this new shoot can then be treated prophylactically to avoid re-infection.

With the low level of disease development that has occurred in the prophylactic vines up to this point, it is difficult to assess with any degree of certainty which treatments have the potential to protect vines from developing PD. The SAR inducing chemicals have held up well in the vineyards that have had some disease development in the controls within the last year. This gives some indication that acquired resistance in grapevines could play an important role in avoiding PD development. Zinc 50 also produced favorable results in 2001, possibly reinforcing the idea that increasing the concentration of metallic ions in the xylem sap can create an environment that reduces infection by Xf.

From the preliminary data obtained in this experiment, copper amino acid chelate shows the most potential in raising the level of available metallic ions that may negatively affect the growth of Xf of all the metal-amino acid chelates that were tested. This information is unfortunate due to the significant level of phytotoxicity that the copper amino acid chelate causes when applied as a foliar spray to grapevines. These results also bring into question the results obtained from nutrient analyses of xylem sap collected from Cabernet and Thompson Seedless vines treated with zinc, manganese, and copper amino acid chelates that showed that very significant increases in the concentration of these metal ions after foliar applications of zinc and manganese chelates. Zinc and manganese amino acid treatments, although shown to raise microelement levels in grapevine xylem to concentrations that would be theoretically inhibitory to Xf, may not produce metallic ion concentrations that are actually toxic to Xf en planta. It is possible that the chelated ions are not free to act as bactericides against Xf cells in the xylem. Experiments designed to test bactericidal properties of xylem sap extracted from a prophylactically treated vine are now being performed in order to develop a standard protocol for screening potential bactericides en planta.

The results, being preliminary, can only give some insight into how increased levels of micronutrients in the xylem sap can negatively affect the growth of Xf. Bacteria growing in the xylem are exposed to the xylem conditions for the duration of their existence and therefore will be subject to a micronutrient increase in the xylem for as long as that increase is present. Therefore, in order to obtain a more realistic view of the potential for negatively altering the xylem conditions for Xf growth, the duration that the bacteria are exposed to the xylem sap will be increased up to 10 days. Also, the concentration of Xf CFUs added to the xylem sap extracts will be increased to allow for higher CFU counts on the plates that will be more accurate than the low CFUs used in this initial screening.

We were very pleased that the results of grapevine inoculation showed that many of the bacterial isolates could multiply and move in grapevine xylem vessels. Additional endophytes collected from field isolations will continue to be screened for systemic movement within grapevine as well as natural antagonism to Xf. In the future, grapevines that were inoculated with endophytes that were recovered at least 6cm above or 6 cm below the point of inoculation will be re-sampled to find out how far the endophyte actually moved within the 4 week period. We find the results of this subset of data promising. Large scale processing of the more than 600 endophytes collected over the past three years is currently under way. We will also be screening non-tumorogenic strains of Agrobacterium vitis acquired from Thomas Burr at Cornell University, and a Bacillus species obtained from Ken Eastwell at Washington State, Prosser, WA for systemic movement in grapevine as well as antagonism to Xf.

A PhD student is studying the inheritance of Xf resistance in Muscadinia rotundifolia. He has completed a broad series of crosses among 12 siblings from an F1 population of Vitis rupestris x M. rotundifolia, with 6 males crossed to each of 6 females. He will test a 4 x 5 mating scheme and evaluate a portion of the seedlings from each of the 20 possible seedling populations for resistance to Xf by using needle inoculation with the ‘Stags Leap’ strain followed by symptom evaluation and ELISA to determine the extent of Xf movement. The results of this research will give estimates for the number of genes involved in resistance. Evaluation of the seedling populations has begun and will be completed over the coming year.

 

Management of Pierce’s Disease of Grape by Interfering with cell-cell Communication in Xylella fastidiosa

Principal Investigator: Steven Lindow

We have determined that Xylella produces a diffusible signal factor that is very likely involved in the expression of virulence traits required for disease symptoms. We have developed a simple screening system that will allow us to test thousands of indigenous bacteria for the ability to interfere with or degrade the signaling system in Xylella. Such strains can then be tested directly for their ability to control disease when introduced into grape. Alternatively, the genes encoding such interfering compounds or degradative enzymes can be introduced into grape so that Xylella virulence genes can be prevented from being expressed, hence preventing disease symptoms. We have developed a genetic system that enables gene-specific knockouts to be made, as well as in gene replacements to enable monitoring of gene expression using various reporter genes. While this system is still being refined, this is a major breakthrough that will enable us, as well as others working on the pathogen, to understand better the processes leading to disease.

 

Understanding the Sexual Life-Cycle of Eutypa lata

Principal Investigators: Peter G Long and Rosie E Bradshaw

A start has been made on determining the basis for sexual reproduction and hence of variability in the fungal pathogen Eutypa lata. This will contribute to a better understanding of the basis of pathogenic variation and of the basis for selecting stable forms of resistance in breeding new varieties and of other approaches to managing this major, worldwide disease problem.

 

Effects of Berry Size and Crop Yield on Wine Composition and Sensory Quality

Principal Investigator: Mark Matthews and JX Guinard

This research has shown that wine made from small berries has greater concentrations of skin tannin and anthocyanins (color) than that produced from large berries, but that the differences are much smaller than predicted from the surface:volume ratios. Is has also shown that imposing late season water deficits increases the concentrations of these solutes independently of the increases that arise from the smaller berry size that is produced from low vine water status; i.e. the altered fruit and wine composition of low irrigated vines is not simply explained by berry size. Water deficits lower yields, but also result in wines with desirable sensory properties of increased fruity characters. When yield was manipulated by pruning without changes in irrigation, higher yields produce slightly smaller berries, but fruit with lower concentrations of skin solutes. Thus, the fruit data support the notion that quality is inversely related to yield. However, descriptive analysis of the wines shows a more complex relationship to yield. We believe that there may be a yield cut-off point where quality starts to drop as crop yield continues to increase, and we are poised to find it with the last set of experimental wines produced in 2001.

 

Evaluation of Selected Mediterranean Wine Grape Cultivars and Clones in Lake/

Mendocino Counties

Principal Investigator: Glenn T. McGourty

This research effort is working towards the goal of offering a wider array of plant materials for wine industry in California so that the wine styles and flavors have many possibilities, and that producers have many niches. The ultimate goal is to express the terroir of the different wine regions with the best possible wines. Since so much of California is warm and sunny, it makes sense to match plant materials from other regions of the world were high quality wine is being made. For us to be successful, we need to evaluate these materials in a systematic way that allows us to know the basic features of the cultivars, and what we can expect in terms of their performance under our conditions. I think that in the last three years, we have made significant progress towards accomplishing these goals.

 

Keys to Management of Glassy-winged Sharpshooter: Interactions Between Host Plants,

Malnutrition and Natural Enemies

Principal Investigator: Russell F. Mizell

This research provides the industry and regulatory agencies with some fundamentally important information on the use of host plants and the underlying mechanisms of how and why (including native hosts, and selected species/cultivars of Vitis) by GWSS adults. This research helps elucidate the behavior of some important natural enemies of GWSS and furthers knowledge of the interactions between host plant chemistry, GWSS and its natural enemies. This research points to the need to continue the screening of Vitis spp and cultivars to identify germplasm that is less susceptible to GWSS and to facilitate the study of the determinants controlling the host plant susceptibility that may be manipulated to reduce Pierce’s disease.

 

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

Principal Investigator: Gary A. Moulton

This research will provide growers with information on promising new, early ripening wine grape varieties, particularly red wine varieties, that are well suited to growing in a cool maritime climate, where they can produce high quality wines with full, fragrant flavor. These new varieties, with unique qualities for varietal and blended wines, would broaden the range and increase the sales potential for growers and wineries. Pinot Noir clones appear adaptable to many western Washington locations, particularly on various rootstocks that enhance early ripening, for producing a very high quality wine. The Pinot Noir rootstock trial will supply growers with knowledge on which to base their future plantings.

 

Xylella fastidiosa Bacterial Polysaccharides with a Potential Role in Pierce’s Disease

Principal Investigator: Neil P. Price

We have chemically analyzed isolated xylem sap and Xylella cultures for Xylella EPS and LPS. However, we have found no evidence for the production of a "xanthan-like" EPS gum. Neither of the techniques used (GC-MS, TLC, LC-MS or NMR) detected EPS either in lab cultures of Xylella or grape xylem sap exudates. EPS production was also monitored during the vine growing season, and again was NOT detected.

Xylella LPS (lipopolysaccharide) has been purified for the first time, has been analyzed by SDS-PAGE, and detected in-gel with a Xylella-specific polyclonal antibody. Significantly, the antibody recognizes the grape-specific (Temecula) LPS, but not LPS from an orleander strain or control bacteria.

Compositional analysis (GC-MS alditol acetates) of the Temecula LPS found equimolar D-Gal and L-Rha. In contrast, the orleander-strain produced an LPS containing far less L-Rha.

We conclude that the grape stain produces an L-rhamnose rich LPS, and that the rhamnose residues are selectively recognized by the Xylella antibody. This antibody also detected LPS in infected grape sap, suggesting the possibility of producing a antibody-based diagnostic kit for field analysis of the Pierce's disease.

 

Map-based cloning of a powdery mildew resistance locus in Vitis

Principal Investigator: Bruce Reisch

We analyzed powdery mildew resistance in 272 vines from the cross between Horizon (susceptible) and Ill. 547-1 (resistant). Segregation for resistance was normally distributed. Our work shows that the actual distance between two DNA markers for powdery mildew resistance identified earlier is actually 12 cM, rather than the 1.8 cM calculated earlier from a small population.

As a result of bulked segregant analysis using AFLP markers, we found 68 candidate markers for mapping to the powdery mildew resistance locus. Efforts have begun to saturate the genetic map in the region of this resistance gene locus. To date, 57 of the 68 markers were examined, yet of these just seven were tentatively placed on the map in the same region as the powdery mildew resistance locus.

New technologies are being developed in other laboratories that may allow a more thorough and detailed analysis of the many genes involved in a plant's defense again disease. Undoubtedly, the material we now possess is unique, and our present knowledge of the map location of this gene for powdery mildew resistance will be of value as new approaches are examined to reach our original goals.

 

Development of Polymerase Chain Reaction for Rapid Detection of Grapevine Leafroll Associated Viruses 1 through 5

Principal Investigator: Adib Rowhani

Specific PCR primers for GLRaVs 1 through 5 were designed, tested and optimized. One step RT-PCR methodology was also developed and the reagents and testing conditions were optimized.

A simple blotting methodology for sample collection in the field was developed. Leaf petioles or young shoots are cut and blotted on specific nylon or nitrocellulose membrane and then these membranes are brought to the laboratory for processing and virus detection. The advantages of this method are: no technical training is required, and if necessary, the samples can be stored for a long time before they are prepared and tested.

In order to develop a reliable RT-PCR detection method, it is very important to identify variations among different isolates (or strains) of each one of these GLRaVs and accordingly design PCR primers that could detect all diverse isolates. In the past year, sequences from the coat protein gene from 10 and 5 different isolates of grapevine leafroll associated virus (GLRaV) -1 and -5, respectively, were compared. The number of nucleotides which were compared from the coat protein gene were 680 and 786 nt for GLRaV-1 and -5 respectively. All GLRaVs-1 isolates used in this study showed 95-99% homology in their compared sequences indicative of a homogeneous population. We had the same observation with GLRaV-5 with again 95-99% homology.

Reliability and sensitivity of RT-PCR for the detection of GLRaVs-1 to -5 was compared with ELISA and with symptom expression of leafroll disease on its biological indicator. From 137 vines tested in this experiment, 26, 16, and 29, respectively tested positive on biological indicator, ELISA, and RT-PCR. The results indicate that the RT-PCR is more sensitive than either indexing on biological indicator host or ELISA. Counting RT-PCR test for GLRaV-5 in this experiment (did not have access to a reliable ELISA reagent for this virus), we found that total of 41 vines were tested positive by PCR which again outnumbers biological index on indicator (27 plants).

 

Physiological Role of Rootstocks in Determining Grapevine Vigor

Principal Investigator: David R. Smart

We have made a key insight into the functioning of grapevine roots that will greatly benefit the industry in several key areas. These areas may not provide growers with specific tools to abate or control diseases per se; however, the results have provided key insights that will allow us to take a more direct mechanistic approach to understanding root related issues such as vine vigor and scheduling a fertility program. These areas can be defined as the question of the relationship between size and maintenance of the root system and overall vigor of the vine, the role of hydraulic redistribution in deficit irrigation and partial rootzone drying, and the role of roots in dry soils in the nutrient economy of the vine. Based on our results, we have taken the appropriate steps to direct our research program towards understanding the above issues in the relevant areas.

 

 

Whole-vine Measurements of Photosynthesis to Determine Physiological Effects of Regulated Deficit Irrigation and Crop Load in Vitis vinifera cv. Cabernet Sauvignon

Principal Investigator: Julie Tarara

The engineering and design work that was proposed for 2001 was completed and has produced an experimental system for the investigators to collect measurements of whole-vine photosynthesis during the upcoming growing seasons. The application of this research equipment to the study of regulated deficit irrigation (RDI) will produce information on physiological effects of RDI and its timing, which will be valuable to the industry in arid areas where RDI is being considered or already is practiced.

 

Grapevine Cold Hardiness: Developing a Data Base for California

Principal Investigator: Robert L. Wample

Development of a low temperature exotherm system that can be used to establish a database for California grapevines. Such a system has not existed to this point.

Beginning of an educational outreach program to make growers more aware of the problem of low temperature injury to grapevines and how their management practices may influence grapevine cold hardiness.

Establishment of a grower group to provide input and support for the project, including the collection and shipping of samples for analysis.

 

Effect of Irrigation Frequency on Productivity of Thompson Seedless Grapevines Grown in the San Joaquin Valley Using Drip Irrigation

Principal Investigator: Larry E. Williams

The lysimeter and the rest of the equipment needed for the successful operation of this study worked without problems in 1999, 2000 and 2001. Measurements of vine water status (midday leaf water potential) indicated that there were differences among the irrigation treatment amounts and trellis type. Midday leaf water potential was also affected by irrigation frequency with results demonstrating that the change in vine water status before an irrigation event (for the once every seven days treatment) was more negative for the deficit irrigated vines than for the full ET treatment after the irrigation took place.

The three treatments (irrigation frequency, irrigation amount and trellis) had significant effects on berry characteristics measured the last three years of this study. There were no significant interactions among the treatments with regard to berry weight, soluble solids and yield in 1999 and 2000. This may be due to the fact that irrigation effects can be cumulative and it may take several years to actually affect vine productivity. There were significant interactions between irrigation amounts and frequency on berry weight, soluble solids and yield in 2001. This was probably due to the delay in initiating the irrigation in the treatments (two weeks after bloom in 2001). The reductions in yield were measured despite the low crop load the vines were carrying in 2001. These results illustrate that the date of initiation of irrigation is an important factor in deficit irrigation management of grapevines. In the 1999 and 2000-growing seasons there were no significant effects of irrigation amounts on yield, this is similar to results obtained in previous years. Therefore, if one wants to increase fruit quality using deficit irrigation but maintain yields, one would need to initiate irrigations earlier in the growing season. This also is true regarding vegetative growth.

 

Establishing Critical Values of N and K for Grapevines

Principal Investigator: Dr. Larry E. Williams

This research has the potential, once all samples are analyzed, to make grape growers cognizant of the fact that; cultural practices, leaf position, sampling technique, time of day samples are collected and weather conditions at the time of sample can affect the nutrient values measured in petioles. In addition, once leaf, stem and cluster N and K are analyzed; the relationship between petiole nutrient values and N and K in those tissues can be shown. This may then be used to establish new critical values of petiole tissue analysis that are independent of cultivar and/or rootstock. For example, an analysis of the relationship between petiole nitrate-N and total N resulted in a highly significant linear regression using data from all locations, dates, time of day and leaf type (sunlit or shaded) (Figure 1). It is anticipated that such may be found when leaf, stem and cluster N and K are correlated with petiole nitrate-N, total N or K.

It should be pointed out that conclusions drawn in portions of this report are based upon a limited amount of data. However, several generalizations can be drawn regarding what may influence the nutrient values of petioles. 1.) The type of leaf chosen to sample, whether it is in the sun, shade or opposite the cluster, will influence the values of nitrate-N and K. Sunlit leaves at bloom generally had higher values of petiole nitrate-N than either shaded leaves or leaves opposite the cluster. At veraison and prior to harvest, shaded leaves had greater values of petiole nitrate-N and K than sunlit leaves. 2.) Irrigation amount (when comparisons between the Irrigated and Non-irrigated treatments were made) had an effect on petiole nitrate-N and K late in the growing season. The irrigated treatment generally had lower values of nitrate-N and K when compared to the non-irrigated treatment. It is unknown at this time whether the water status of the vine is responsible for this effect. 3.) The three cultivars used in this study generally responded to the treatments and sampling differences similarly. 4.) Without further petiole analysis of more replicates, it is unknown whether time of day samples are collected or the contribution of the petiole’s sap to the total nutrient within the petiole significantly affects nutrient.

 

Interaction of Irrigation Amounts and Canopy Management Practices on Grapevine Water Relations, Berry Characteristics, Productivity and Wine Composition

Principal Investigator: Larry E. Williams

Once this study is completed we should have a better understanding of the effects of canopy management practices on cluster water status and whether this might contribute to the perceived effects of light on fruit quality in the field. The data may also indicate that a higher priority should be given to irrigation management in the vineyard. Proper irrigation scheduling with the appropriate water amounts may result in a canopy where little or no canopy management practices are necessary.

 

Evaluation of Zinfandel Heritage Selections

Principal Investigator: James Wolpert

The original Heritage vineyard (Phase 1) is comprised of 57 selections from 27 vineyards in 6 counties in addition to 3 certified Zinfandel and 3 certified Primitivo clones. Wide variance in cluster wt and berry wt has been seen, although the differences have not been consistent over the past three years. The one major exception is Primitivo selections, which have had the lightest cluster and smallest berries. Phase 2 of the vineyard added another 27 selections from 8 previously unrepresented counties. In 2001, 22 virus-free selections were expanded into a replicated trial with enough vines for much larger wine lots. The outcome of this work will be the release of certified Zinfandel selections that have been highly scrutinized for yield components, fruit quality indices and wine attributes. The involvement of Zinfandel Advocates and Producers in the evaluation and selection of released materials will help ensure usefulness to industry.

Field Evaluation of Winegrape Rootstocks

Principal Investigator: James Wolpert

This decade-long series of trials was concluded with the winter 2002 pruning wts. A Cooperative Extension publication tentatively entitled "Rootstocks for Winegrapes in Coastal and Northern California" is in preparation in conjunction with six UC farm advisors. When completed, the publication will a key grower resource for selection of rootstocks in future winegrape vineyards. While the publication is likely to include general information, in addition to experimental data, that a grower needs to choose a rootstock, the AVF-funded project will provide the foundation on which the recommendations rest.