Description and Performance

After selection in 1999 and initial field evaluation in Tallahassee, hardwood cuttings were sent to Texas for testing. Nine A24-6-6 vines were grafted on ‘Kober 5BB’ rootstock and planted in Industry, Texas, for field evaluation. The soil at the site, as classified by the US Department of Agriculture Natural Resources Conservation Service (USDA-NRCS), was a Cuero loam with a pH of 8.2. Vines were trained to a mid-wire bilateral cordon training system with vertical shoot positioning (VSP). The row × vine spacing was 3.05 m × 2.44 m. Data collected at Industry in 2012–15 on fruit characteristics included harvest date, berry weight (based on a 100-berry sample collected once each season), soluble solids using a handheld refractometer, titratable acidity, and pH. The control cultivar used for comparison, ‘Blanc Du Bois’, was also grafted on ‘Kober 5BB’ and grown using the same practices as the ‘Blanc Du Soleil’ including vine spacing and training.

In Goliad, 90 own-rooted vines were planted in 2015 and produced fruit beginning in 2017. The vines in the trial were trained using the Watson Training System (Scheiner et al. 2020) at a row by vine spacing of 3.66 × 2.44 m. Viticulture data collection for 2018–22 at Goliad included budbreak, bloom, and harvest dates; soluble solids; titratable acidity; pH; and, in 2018 and 2019, yield per vine, cluster weight, berry size, and dormant pruning weight. The soil at the Goliad site was a Raisin loamy fine sand with a pH of 7.5 (USDA-NRCS). The comparison cultivar, ‘Blanc Du Bois’, was planted in 2014. Vines were also trained to the Watson Training System at a row by vine spacing of 3.66 × 2.44 m, and the management practices performed were the same as the ‘Blanc Du Soleil’.

Wines were produced in 2018 and 2019 using a standard protocol for microvinification. Whole clusters were pressed using a water press at 3 bars, and the juice was cold settled at 5 °C for 24 h followed by racking to remove solids. Sulfur dioxide was added as potassium metabisulfite at a rate of 30 ppm. The juice was inoculated with EC-1118 yeast at a rate of 0.26 g/L and fermentation was carried out at 15.56 °C until dryness (<0.5 g/L). Wines were subsequently racked several times for clarification, then cold stabilized. Immediately before bottling, 20 ppm sulfur dioxide was added. After 6 to 10 months, wines were analyzed for ethanol, color, and acidity, and informal sensory evaluations were carried out with wine industry members, students, and faculty at Texas A&M University.

In Tallahassee, a five-vine plot of own-rooted vines was established in 2017. Vines were trained to a high-wire bilateral cordon training system. The row by vine spacing was 3.04 × 2.44 m. The first crop was produced in 2019, and data were collected in 2019–22 on budbreak and harvest date, berry weight, berry size, cluster weight, number of berries per cluster, soluble solids, juice pH, and titratable acidity. The soil at the site, as classified by the USDA-NRCS was an Orangeburg fine sandy loam.

Wines were produced in years 2019–21 at the Florida A&M University (FAMU) Center for Viticulture & Small Fruit Research (CVSFR) using a similar winemaking protocol as in Texas with minor modifications. Clusters were processed using a manual crusher/destemmer and pressed with a membrane hydro-press for two cycles at 2.8 bars. Sulfur dioxide (35 ppm) was added as potassium metabisulfite during processing. Static racking was performed on the juice after cold settling for 24 h. The clarified must was inoculated with VL1 yeast from Laffort at a rate of 0.25 g/L and fermented at 18 °C until dryness (<0.5 g/L). After fermentation was complete, two additional static rackings were performed to achieve clarity. Before bottling, sulfur dioxide was added to reach 1.0 ppm molecular SO₂. Wine samples were stored at 21 °C for 3 to 6 months before being analyzed for vinification parameters (density, alcohol % v/v, glucose, fructose, net dry matter, pH, total acidity, volatile acidity, malic acid, lactic acid, free and total sulfur dioxide, and chromatic characteristics) and bioactive compounds using the Wine Analytical Laboratory at the FAMU CVSFR.

All analysis were conducted according to the International Organization of Vine and Wine (OIV) Compendium of International Methods of Analysis. Density and specific gravity were measured using a Gibertini DensiMat gravimetric scale (Gibertini, Novate Milanese, Italy). Percent alcohol (v/v) and volatile acidity was determined with Gibertini Distillatore Elettronico Enochimico. Glucose, sucrose, malic, and lactic acid were measured using a Bio-Rad SmartSpec^TMPlus (Hercules, CA, USA) spectrometer and enzymatic kits from Randox Food Diagnostics (Crumlin, UK). Net dry matter was calculated using OIV methods based on density and sugar content. Juice pH was measured using a Jenway 3510 pH meter. Total acidity was measured using OIV 0.1M sodium hydroxide titration. Sulfur dioxide was measured using Ripper titration. Color was analyzed using the spectrophotometer to measure the absorbance at 420-, 520-, and 620-nm wavelengths. Intensity was calculated using OIV methods.

Standard cultural practices for bunch grape culture were practiced at all trial sites including annual dormant pruning, weed control using mechanical and chemical methods, and drip irrigation applied as needed. Annual N applications and complete fertilizers were used for fertilization on demand.

Fungicides were applied to control black rot (Guignardia bidwellii Viala & Ravaz), powdery mildew {Erysiphe necator Schw. [syns. Uncinula necator (Schw.) Burr., E. tuckeri Berk., U. americana Howe, and U. spiralis Berk. & Curt; anamorph Oidium tuckeri Berk.]} and downy mildew (Plasmopara viticola Berl. & de Toni), and anthracnose (Elsinoë ampelina Shear) as per commercial requirement for the area (Scheiner et al. 2022). Insecticides to control PD vectors were not applied at any research site.

Yield characteristics.

Vines at all trial locations were pruned to one- to two-bud spurs annually. In Texas, bud fruitfulness (percentage of shoots bearing clusters) ranged from 86.48% to 87.65% with yields ranging from 2.59 to 3.97 kg per vine in Goliad. In Tallahassee, yields ranged from 3.1 to 3.7 kg per vine, an acceptable yield for commercially wine grape production in the region.

The clusters of ‘Blanc Du Soleil’ are medium-sized, often shouldered, and cylindrical. Cluster weights in Goliad ranged from 79.44 to 106.46 g. In Florida, cluster weights were larger averaging 168.8 to 235.1 g. ‘Blanc Du Soleil’ clusters are moderately to well filled with medium-sized, light green– to bright yellow–colored berries (Figs. 2 and 3). Berry weights averaged 1.97 g in Industry (Table 1), 1.84 g in Goliad (Table 2), and 2.90 g in Tallahassee (Table 3).

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Table 1.Fruit characteristics for ‘Blanc Du Soleil’ and ‘Blanc Du Bois’ at the Industry, TX, USA, research site in 2012–15.

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Table 2.Fruit and vine characteristics of ‘Blanc Du Soleil’ and ‘Blanc Du Bois’ at the Goliad, TX, USA, research site in 2018–19.

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Table 3.Fruit and vine characteristics of ‘Blanc Du Soleil’ and ‘Blanc Du Bois’ at the Tallahassee, FL, USA, research site in 2019–21.

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Fruit composition and quality.

Soluble solids averaged 17.20% in Industry (Table 1) and ranged from 17.48% to 16.86% and 19.0% in Goliad (Table 2) and Tallahassee, respectively (Table 3). Soluble solids were comparable to ‘Blanc Du Bois’ at all locations, but ‘Blanc Du Soleil’ retained greater acidity. Wine pH was lower and titratable acidity was higher for ‘Blanc Du Soleil’ at both locations in Texas, which may be valuable for warm climate regions where high pH may result in problems with wine stability.

Wine pH and titratable acidity of ‘Blanc Du Soleil’ ranged from 3.09 to 3.20 and 6.8 to 8.9 g/L, respectively, in Texas. In Florida, wine pH ranged from 3.06 to 3.22 and titratable acidity ranged from 8.2 to 9.8 g/L (Table 4). Malic acid was less than 2 g/L in the Texas wines and less than 2.6 g/L in the wines from Florida indicating that most of the acid present was tartaric acid (Table 4). Overall, fruit quality based on chemical composition was observed as high, and less fruit rot was noted in ‘Blanc Du Soleil’ fruit than ‘Blanc Du Bois’ in neighboring plots.

Table 4.Chemical composition of ‘Blanc Du Soleil’ wines produced in Texas and Florida, USA.

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Vine characteristics.

In Goliad, budbreak was observed between 25 Feb and 5 Mar, a few days before ‘Blanc Du Bois’. In Tallahassee in 2019, budbreak occurred on 26 to 28 Feb, 6 d later than ‘Blanc Du Bois’. In Texas and in Florida, ‘Blanc Du Soleil’ was harvested from 129 to 136 d after budbreak, slightly later than ‘Blanc Du Bois’ but still considered early season compared with ‘Black Spanish’, a PD-tolerant red wine grape cultivar widely grown in the Texas Gulf Coast.

In Goliad and Tallahassee, ‘Blanc Du Soleil’ was observed to have good vigor on its own roots but was less vigorous than ‘Blanc Du Bois’. In Goliad, ‘Blanc Du Soleil’ vines had dormant pruning weights that averaged 1.31 and 1.41 kg in 2018 and 2019, respectively vs. 1.79 kg/vine for ‘Blanc Du Bois’ in 2018. In Goliad, magnesium deficiency was observed in both ‘Blanc Du Soleil’ and ‘Blanc Du Bois’ and confirmed with tissue testing, but visual deficiency symptoms appeared to be worse in ‘Blanc Du Soleil’, suggesting that it may be more prone to magnesium deficiency when grown on its own roots.

The growth habit of ‘Blanc Du Soleil’ is semierect and is suitable for low- or mid-wire training systems with VSP and high-wire systems. The cold hardiness of ‘Blanc Du Soliel’ has not been evaluated, but in 2021, winter temperatures reached –11 °C in Goliad with no injury observed to buds and canes.

The most valuable characteristic of ‘Blanc Du Soleil’ is its survival capacity and high fruit and wine quality potential in the Gulf Coast, a region of the United States that has extreme pressure from PD (Kamas 2014). Although formal testing for PD tolerance has not occurred, its survival and lack of symptoms for 23 years suggests tolerance or some level of resistance. Vine survival at all sites was 100% over the course of evaluation. Furthermore, both parents of ‘Blanc Du Soleil’ are tolerant to PD.

There are no substantial data to support fungal disease resistance of ‘Blanc Du Soleil’ to common diseases such as black rot, powdery and downy mildews, or anthracnose, but observations in Texas and Florida suggest that ‘Blanc Du Soleil’ has better resistance to downy mildew than ‘Blanc Du Bois’. In Goliad, downy mildew was observed in ‘Blanc Du Bois’ after periods of intense pressure, but ‘Blanc Du Soleil’ had few visible symptoms.

Wine characteristics.

Observational data on wines produced suggests that ‘Blanc Du Soleil’ has high wine quality potential with no off flavors or “hybrid” characteristics. Wine flavor was compared with ‘Pinot Gris’ with flavors of pear, apple, peach, and pineapple commonly noted. Wine flavor was described as distinct from ‘Blanc Du Bois’, which is known for producing aromatic wines.

‘Blanc Du Soleil’ should be considered for white wine production in the southern United States. Its excellent quality potential and disease resistance are primary attributes. PD tolerance or resistance is a major positive characteristic and should be of value to grape growers in areas where this disease poses a significant risk.

Availability.

Florida A&M University is the assignee for the US patent of the ‘Blanc Du Soleil’ grapevine (Ren et al. 2022). Nurseries interested in propagating these cultivars must sign a license agreement with the Florida A&M Technology Transfer, Licensing and Commercialization Office (https://www.famu.edu/administration/ research/office-of-technology-transfer-and-export-control/index.php). Contact the Technology Transfer, Licensing and Commercialization Office, to inquire about the propagation of ‘Blanc Du Soleil’ grapevine or FAMU/Center for Viticulture (www.famu.edu/viticulture) for any additional information as needed.