Evaluation of New Winegrape Varieties for the San Joaquin Valley

Fifty six different red and white wine grape selections are being evaluated at the Kearney Agricultural Center, in Parlier, CA. These varieties were originally selected because they originate from warm-climate Mediterranean regions, and/or were believed to have traits that would be desirable in a warm climate wine region, like the San Joaquin Valley. Most of the selections tested were relatively recently released to the industry from Foundation Plant Services and had not been previously evaluated in California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned, leaving 8 to 10 two-bud spurs per meter of cordon. However, beginning in 2013, certain varieties have also been subjected to simulated mechanical pruning. Grapes were harvested according sugar accumulation, with the harvest target for white varieties at 22° Brix, and reds at 25° Brix. A few select varieties were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic juice chemistry were determined for all 56 varieties. As was typical in the region for 2015 and similar to 2014, the early ripening varieties were harvested earlier than in previous years. The first harvest occurred on 28 July 2015, and included Erbaluce, Petit Manseng, and Picolit. Fiano, typically the earliest variety harvested, followed soon after on 30 July 2015. Having failed to meet the desired Brix threshold for harvest, hand-pruned Parellada, Vernaccia Nera, and Counoise, and mechanically pruned Counoise, Caladoc, and Corvina Veronese, were harvested at the end of the season in early November. Total yields (inclusive of rot) ranged from 5.53 kg/vine (Carmenere) to 26.75 kg/vine (hand pruned Counoise). For the simulated mechanical pruning selections, yields were generally similar or greater than their hand pruned counterparts, with the exception of Counoise. Mechanical pruning either did not affect or reduced rot incidence for varieties harvested before October. But for the late ripening varieties, the late harvest required, probably due to overcropping in the mechanically pruned treatment, increased rot incidence in Corvina Veronese and Caladoc. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Twelve varieties which performed very poorly in the first two years of the trial were topworked to new selections in 2014 and used to make wine in 2015. From the work done in previous years, the most promising varieties were identified and, combined with the newly grafted varieties, a total of 23 selections were made into wine at Constellation Brand’s experimental winery and the finished wines will be evaluated and presented in the coming year. A selection of varieties that have been consistently poor performers with regards to rot and late ripening have been identified and are good candidates to be grafted over into more-promising selections in the future of this variety trial.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

Fifty six different red and white wine grape selections originating from warm-climate Mediterranean regions, and/or believed to have traits that would be desirable in a warm climate wine region, are being evaluated at the Kearney Agricultural Center, in Parlier, CA. Most of the selections tested were recently released to the industry from Foundation Plant Services, so certified selections have not previously been evaluated in California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon. However, beginning in 2013, certain varieties have also been subjected to simulated machine pruning. In general, we attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, but certain selections were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic chemistry were determined and wine lots were made from some selections at Constellation Brand’s experimental winery. Many varieties were harvested earlier in 2014 than they were in previous years. Fiano, a white variety, has typically been the earliest variety harvested (early August), but several other early whites and a red variety were also harvested on 11 August 2014, the same day as Fiano. About a half dozen red and white varieties failed to meet their target soluble solids level even though the last harvests occurred in early November. Yields ranged from less than 4 kg per vine for Prieto Picudo to about 30 kg of fruit per vine from the machine-pruned Counoise, a red variety. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Wines from the trial will be made available for tasting and analysis in 2015, as they have been in most of the past several years. Twelve varieties which performed very poorly in the first two years of the trial were topworked to new selections in 2014, with full crops expected in 2015. Some varieties were subjected to simulated machine pruning to determine if yield and rot problems could be ameliorated. In most cases, machine pruning substantially reduced rot and increased yields, but the higher yield severely delayed ripening of some varieties and, in Falanghina, was associated with slightly higher levels of rot.

Evaluation of Grapevine Rootstock Selections

A team of academic, government, and industry partners developed a plan for evaluating nearly 700 rootstock selections from a USDA-ARS rootstock breeding program. All the vines were assessed for desirable traits, including the production of abundant, well-matured canes of adequate diameter, length, and internode spacing, with minimal lateral shoot growth, powdery mildew scars, freeze damage, or fruit production. Based on these criteria, 240 vines having very poor traits were identified and discarded, and 30 selections with very good traits were prioritized for further evaluation. Cuttings from the high-priority selections were distributed to several academic and industry labs, where their rooting ability, nematode resistance, and virus status were tested. These tests narrowed the high priority list to six virus-free stocks which were resistant to aggressive strains of root-knot nematodes (RKNs). Some of the six high-priority vines rooted poorly in one or both cooperator’s labs. Weak rooting is unacceptable, and may confound nematode resistance testing, so we propose to retest these selections, using more cuttings, and benefitting from the expertise of a commercial grapevine nursery. Most of the remaining selections were eliminated because they were found to be susceptible to RKN by one or both labs, or they rooted poorly in both labs. One RKN-resistant selection rooted very well but tested positive for SyV-1 and RSP viruses, so it will be forwarded to Foundation Plant Services for virus elimination; testing on this selection will resume after clean plant material becomes available. Four additional rootstock selections were added to the high priority list based on the performance of Syrah when grafted to those stocks. Cuttings from those four selections will be distributed to the cooperators for advanced testing.

Evaluation of new Winegrape Varieties for the San Joaquin Valley

A wine grape variety trial was established in 2008 at the Kearney Research and Extension Center, a warm climate region. The trial consists of 55 16-vine plots, each planted to a different red or white wine grape selection originating from warm-climate Mediterranean regions, and/or believed to have traits that would be desirable in a warm climate wine region. Most of the selections tested were recently released to the industry from Foundation Plant Services so, in many cases, certified selections have never been evaluated in California. All vines are on 1103P rootstock and in 2011 and 2012, the first two cropping years, all vines were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon; in 2013, certain varieties were subjected to simulated machine pruning, or cane pruning.

In general, we attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, but certain selections were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic chemistry were determined and wine lots were made at Constellation Brand’s experimental winery. The varieties were harvested across a wide range of dates starting with a white cultivar, Fiano, in early August, and ending with about a half dozen red and white varieties that were harvested on the last day of October. Yields ranged from less than 6 kg per vine for Prieto Picudo to more than 50 kg of fruit per vine from the machine-pruned Tocai fruliano, a white cultivar. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Berries from red varieties also varied widely in their content of anthocyanins, tannins, and other phenolic compounds.

Most varieties had slightly higher anthocyanin content in 2013 than they did in 2012, and Bonarda and Segalin noir have consistently had the highest anthocyanin content of the varieties tested. Wines from the trial will be made available for tasting and analysis in 2014, as they have been in each of the past several years. Twelve varieties which performed very poorly in 2011 and 2012 were topworked to new selections in 2013, and some varieties were subjected to different canopy management practices to determine if yield and rot problems could be ameliorated. Shoot tucking generally had little if any affect on fruit quality or rot, but simulated machine pruning greatly increased yields and reduced rot of most varieties subjected to this practice. Additional years of data are needed to determine if the high yields of machine-pruned vines are sustainable and whether or not they adversely affect fruit or wine quality.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

A wine grape variety trial was established at the Kearney Research and Extension Center, a warm climate region. The trial consists of 55 16-vine plots, each planted to a different red or white wine grape variety selected from warm-climate Mediterranean regions. Most of the varieties tested were recently released to the industry from Foundation Plant Services so, in many cases, certified selections of these varieties have never been evaluated in California. All vines were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon.

We attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, though inclement weather forced the harvest of a few slow ripening varieties in early November, before they were completely ripe. At harvest, yield components, rot incidence, and basic chemistry were determined and, for 25 of the 55 varieties, wine lots were made at Constellation Brand’s experimental winery.

The varieties were harvested across a wide range of dates starting with a white cultivar, ‘Fiano’, on 18 August, and ending with 15 red and white varieties which were harvested in the first week of November. Yields ranged from a meager 2.32 kg per vine from the red cultivar Carmenere, to more than 35 kg of fruit per vine from the white cultivar ‘Trebbiano Toscano’. Harvest date was poorly correlated with yield, but there was a relatively strong positive correlation between rot incidence and harvest date.

Yield of red and white varieties was more strongly correlated with cluster weight than with the number of clusters per vine, and cluster weight was more strongly correlated with the number of berries per cluster than with berry weight. Red and white varieties varied widely with respect to pH and titratable acidity. Other fruit composition data were collected by Constellation and will be shared in a future report. Wines from the trial will be made available for tasting and analysis in 2012.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

Twenty winegrape varieties were planted for viticultural evaluation at the Kearney Research and Extension Center (Table 1). Degree days, calculated from March 15 thru October 15 using a threshold of 50??F, regularly reach 4500 placing it in region V on the Winkler scale. Many the varieties are being evaluated in California for the first time. We believe that newly imported winegrape varieties from around the world may have beneficial characteristics that will make valuable contributions to the California wine industry. Identifying these varieties is the goal of this continuing research. The first usable data was collected from this trial in 2007. Therefore the 2010 season provides the opportunity to present both the current year?s data and average data from four years. All varieties were pruned and shoot thinned to 15 shoots per meter. The protocol called for all varieties to be harvested at 24 Brix. In 2010 harvest occurred from September 9 to October 20, a 41 day period. Mean harvest Brix across all varieties was 24.1. Eleven varieties were harvested within 0.5 Brix of the 24 Brix goal. Tempranillo was harvested on the last day at only 20 Brix and was no longer accumulating sugar. Yield ranged from 2.7 ton/acre (Carmenere) to 12.3 (Grenache). Interest in this project resulted in a collaboration with Constellation Brands, Madera. For the third year Constellation agreed to make wine from selected varieties. The results will help us more thoroughly describe these varieties. A detailed review of each of the 20 varieties is included in the interim report. Recommended varieties include Durif (Petite Sirah), Petit Verdot and Tannat. The cooperation of Constellation Brands, Madera in Brix sampling and in winemaking and analysis is greatly appreciated.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

Twenty winegrape varieties are planted for viticultural evaluation at the Kearney Research and Extension Center (KREC). Degree days, calculated from March 15 thru October 15 using a lower threshold of 50° F, regularly reach 4500 placing it in region V on the Winkler scale. Many the varieties are being evaluated in California for the first time. We believe that the world holds many winegrape varieties that are capable of making valuable contributions to the California wine industry but are untested in California. Identifying these varieties is dependent on continued research.

Data was first collected from this trial in 2006. During that season several deficiencies in the trial design were identified. It was apparent that modifications to the trellis and irrigation schedule were required. These modifications were made prior to the 2007 season. As a consequence of these changes it was determined that data collected in 2006 would not be included in mean calculations made over years. The 2008 season therefore, provides the first opportunity to present both the current year’s data and average data from multiple years.

In the 2008 season, as in previous years, all varieties were pruned to 15 shoots per meter and excess shoots were removed. No attempt was made to adjust cluster size or clusters per shoot. Measurements of leaf water potential made across varieties were employed to schedule irrigation frequency and volume. The protocol called for all varieties to be harvested at 24º Brix.

In 2008, harvest occurred from September 9 to October 15, a 36 day period. Mean harvest Brix across all varieties was 23.9. Ten varieties were harvested within 0.5 Brix of 24 Brix. Three of five varieties harvested more than 0.5 below 24 Brix were harvested on the last day and may be considered over-cropped. Yield ranged from 6.5 to 19.0 kg per vine, Carmenere and Cinsaut respectively. Cluster weight was the yield parameter most correlated to both yield and cluster rot. Cluster rot was greatest for Cinsaut where almost 15{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the crop was lost to rot.

From a winemaker’s perspective, winegrapes grown in warm regions often have the undesirable characteristics of high pH and low acid at harvest. In 2008 half of the varieties had pH values above 3.75 and another half had titratable acidity below 6.0 g per L. Among the varieties in this trial Tannat stood out as a variety with high acid and low pH. Juice of Tannat at 25.3 Brix had titratable acidity of 6.8 g per L and 3.46 pH in 2008.

Careful attention to plant water status by Larry Williams provided the data necessary for him to properly manage vineyard irrigation. In addition to managing irrigation plant water status measurements are revealing varieties that may be more efficient in their water use. In particular Tinta Francisca has higher leaf water potential than the other varieties following the same level of irrigation.

Interest in this project resulted in a collaboration with Constellation Brands, Inc. Constellation agreed to make and analyze wine from nine of the 20 varieties in the plot. The results will help us more thoroughly describe these varieties.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

Harvest extended over 5 weeks, from 23 August to 2 October, a week longer than 2006. The range of yield was large, from 3.2 kg/vine to 22.7 kg, or 2.7 ton/acre to 18.2 tons (Table 3). The potential yield was even higher had there been no losses to rot or shrivel. Percent crop loss differed greatly from zero to 70{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}. But most of the varieties either had none or less than about 5{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} crop loss (13 out of 20). Cluster numbers differed from about 40 to 65. We strive to leave similar bud numbers (15 shoots/m) in order to obtain similar cluster numbers, however this is not always possible. When we obtain shoot number at pruning, we will ascertain whether clusters number differences are due to different clusters initiated per shoot or to different shoot numbers per vine. Cluster wt differed dramatically from a low of 119 g (Carmenere) to 494 g (Cinsaut). Cluster wt was driven by both berries per cluster and berry wt. Berries per cluster ranged from a low of 72 (Carmenere) to a high of 250 g (Tannat) and berry wt from a low of 1.2 g (Petite Verdot) to a high of 3.4 g (Cinsaut).

In 2007, we harvested sound clusters from defective. Unlike 2006, however, we separately accounted for rot vs. shrivel. Five cultivars had rot levels of 4-6 clusters per vine (about 10{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}) while the rest had 0 to 2 clusters. Severe losses were evident due to shrivel was 37 clusters in Souzao and 15 clusters in Durif. By shrivel we mean the physiological disorder where the cluster rachis dries and the berries completely shrivel. In these clusters there is not sign of rot and the cause of this disorder is unknown. Thirteen cultivars showed no signs of shrivel at all.

Brix ranged from about 21 to more than 25. Most pH values were 3.7 and higher. However a few varieties stood out in 2007 as having a reasonably high ripeness level including (Brix, pH): Aglianico (23.4, 3.41), Montepulciano (22.7, 3.30) and Tannat (25.2, 3.61). Two of those had reasonable yields and relatively low loss (yield [t/a] and loss {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}): Aglianico (12.6 and 4.2{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}) and Montepulciano (10.5 and 0{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}).

Thanks to work by Larry Williams, we were able to better control growth by judicious use of irrigation regime.

Evaluation of Wine Grape Cultivars & Clones for the San Joaquin Valley

In separate trials, the yield, yield components, fruit composition, and susceptibility to sour rot of Barbera, and Syrah grapevine selections, and of several generic white wine grape cultivars (French Colombard, Grenache Blanc, Triplett Blanc, and T182­4), were evaluated at the Kearney Agricultural Center, in the central San Joaquin Valley. Barbera clone 6 was the earliest maturing, having similar or higher soluble solids and pH, and similar or lower titratable acidity than the other clones even though it was harvested one week earlier than the others. Barbera clones 2, 3, and 5 produced 25{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} more fruit, by wt, than clones 4 and 6. Clone 2 always had heavier berries than clones 3, 4, and 5, and those clones had heavier berries, and clusters, than clone 6. Clone 6 had fewer berries per cluster than clones 3 or 5 and had much less sour rot than the other clones, which may make it a desirable selection for the San Joaquin Valley. There was considerable variation among Syrah clones with respect to phenology, fruit composition, and yield. Clone 99 commenced growth soonest, and vines of clone 1 were the last to begin growing. Clone 99 bloomed a few days earlier than clones 1 or 3, but the fruits of clone 1 matured earliest as evidenced by their much greater soluble solids, higher pH, and lower TA than that of most other clones. Fruits of clone 174 matured later than those of clones 1, 100, Shiraz 03, and Shiraz 07, as evidenced by clone 174?s lower soluble solids and pH. Clones 03 and 100 had exceptionally high yields, between 20 and 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} greater, than most other selections. The high yields of clone 03 could be attributed to the fact that it had the most clusters per vine and its clusters were among the heaviest of the selections tested due to its relatively heavy berries. In contrast, the high yield of clone 100 was mostly due to its exceptionally heavy clusters which resulted from it having among the most berries per cluster, and the heaviest berry weights, of the selections tested. Clone 99, whose yield was similar to clone 100, had among the lowest levels of sour rot, and its fruit composition was comparable to that of many other clones. Thus, in this early stage of evaluation, clone 99 is one of the most promising Syrah selection. Grenache Blanc matured much earlier than the other varieties as evidenced by its relatively high soluble solids and earlier harvest date. The other varieties were harvested at soluble solids levels that were comparable to each other, but this required harvesting Triplett Blanc and 182­4 about three weeks after Grenache Blanc and French Colombard. Grenache Blanc and Triplett Blanc had about 40{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} greater yields than French Colombard or 182­4. The high yields were due to their relatively high number of clusters per vine and average cluster wts. Sour rot incidence varied from 20­30{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}, but did not differ among varieties. All things considered, Grenache Blanc was superior to the other varieties in having very high yields and relatively early fruit maturity

Development of a Low Density PCR Array (LDPA) for Detection of Pathogens in Grapevines

The goal of this project is to develop a sensitive and reliable molecular method for the detection of viruses in grapevine. This method is called “Low Density PCR Array” (LDPA) and is a derivative of real time RT-PCR using TaqMan probe (TaqMan RT-PCR). LDPA system uses a fluorescently tagged TaqMan probe and it fluoresces in the presence of target viral RNA in an incremental level following each PCR cycle. The released fluorescent signal then is analyzed by a laser-based thermocycler and evaluated.

In the year 2006-2007 we have optimized the buffer for the 6700 automated Nucleic Acid Workstation for sample preparation and RNA extraction for use in LDPA system. The results showed that the 2X ABI lysis buffer (from Applied Biosystem Inc.) worked better than 1X for grapevine tissue and it was comparable to the expensive and time consuming RNeasy column kit procedure by Qiagen Inc. The 6700 automated system is quite fast and inexpensive and uses a 96 well plate format and can prepare RNA from 96 samples in approximately 2 hours. In an experiment we tested 29 vines by TaqMan RT-PCR for Grapevine leafroll associated virus (GLRaV) types 2 and 3 by comparing the 1X and 2X lysis buffer and the Qiagen system. In this experiment we found that 15, 12 and 19 plants were tested positive for GLRaV-2 by using Qiagen, 1X and 2X buffer, respectively. For GLRaV-3 the numbers tested positive were 9, 7 and 9 respectively. This comparison revealed that the 6700 automated system produces high quality RNA and was comparable to the RNA extracted by the Qiagen method.

We also designed primers and TaqMan probes for 14 different viruses in grapevine and their evaluation and optimization for use in LDPA system is in progress. These viruses included GLRaV-1 to -7 and -9; GLRaV-2-RG; Grapevine fanleaf virus (GFLV), Grapevine fleck virus (GFKV), Rupestris stem pitting associated virus (RSPaV); Grapevine virus A (GVA) and B (GVB). LDPA system was evaluated for two viruses, GLRaV-2 and GLRaV-3 and the results were compared with RT-PCR, TaqMan RT-PCR, ELISA and biological index on Cabernet Franc indicator host. In this experiment 29 grapevines were tested. The results showed that 23 plants were tested positive either for GLRaV-2 or -3 or both by LDPA method (using 2X lysis buffere for RNA preparation) and by TaqMan RT-PCR. However, 22, 13 and 12 of these plants were positive by RT-PCR, ELISA and biological index, respectively