Paolo Sabbatini

Postveraison application of antitranspirant di-1-p-menthene to control sugar accumulation in sangiovese grapevines

The effectiveness of a postveraison application of the film-forming antitranspirant Vapor Gard (VG, a.i. di-1-p-menthene) was investigated as a technique to delay grape ripening and reduce sugar accumulation in the berry. The study was carried out over the 2010–2011 seasons in a nonirrigated vineyard of cv. Sangiovese in central Italy. Vapor Gard was applied at 2% concentration to the upper two-thirds of the canopy (most functional leaves) and it significantly lowered leaf assimilation and transpiration rates and increased intrinsic water use efficiency. The Fv/Fm ratio was not modified, emphasizing that photoinhibition did not occur at the photosystem II complex, whereas the reduction of pool size of plastoquinone matched well with reduced CO2 fixation found in VG-treated vines. In both years VG treatment reduced the pace of sugar accumulation in the berry as compared to control vines, scoring a -1.2 Brix at harvest and wine alcohol content at −1% without compromising the recovery of concentrations of carbohydrates and total nitrogen in canes and roots. Concurrently, organic acids, pH, and phenolic richness of grapes and wines were unaffected, whereas there was a decrease in anthocyanin content in the berry (−19% compared to control vines) and in the wine (−15% compared to control vines). The application of VG at postveraison above the cluster zone is an effective, simple, and viable technique to hinder berry sugaring and obtain less alcoholic wines. To be effective the spraying should be performed at ~14 to 15 Brix, making sure that the lower leaf epidermis is fully wetted by the chemical.

Postbudburst Spur Pruning Reduces Yield and Delays Fruit Sugar Accumulation in Sangiovese in Central Italy

The influence of pruning date on yield control and ripening rate of spur-pruned Sangiovese grapevines was investigated over two years (2013 and 2014). Winter pruning was applied on 1 or 4 Feb (mid dormancy); 1 or 5 March (late dormancy); 2 or 7 April (bud swell); 2 or 7 May (flowers closely pressed together); and 1 or 6 June (40 to 50% of flower caps fallen), respectively. Vine yield and fruit composition at harvest were not affected by shifting from the standard pruning dates of mid and late dormancy to the bud swell stage. In contrast, the number of inflorescences in compound buds was significantly reduced for vines pruned in early May. No inflorescences were retained on vines pruned at the beginning of June. Early May pruning reduced fruit set and berry weight and slowed fruit ripening compared to the other pruning dates. At harvest, must soluble solids and titratable acidity were 1.6 Brix lower and 1.8 g/L higher, respectively, for the May treatment compared to the standard pruning dates. The early May pruning dates also achieved higher total anthocyanins and phenolic concentrations than the standard pruning dates, indicating that this technique can potentially decouple the accumulation dynamics of these components. Further studies are needed to better calibrate winter pruning date for managing yield and berry maturation rate.

Spatial and Temporal Study of Climatic Variability on Grape Production in Southwestern Michigan

Daily climatic data were obtained from several sources to calculate growing degree days (GDD) for multiple sites in southwest Michigan, which contains the Lake Michigan Shore American Viticultural Area. The data were examined for spatial and temporal (1950 to 2011) patterns and trends over the region in order to better quantify the role of Michigan climate on juice grape production. The occurrence and severity of frost and freezing temperatures were also considered in this study, as subfreezing temperatures in late spring and early fall can have severe impacts on the region’s juice grape production and fruit quality at harvest. Michigan’s cool-cold climate has warmed in recent decades, particularly since 1980, with an average increase over the region of more than 3.7 GDD (base 10°C) per year. Southwestern Michigan was also found to have higher seasonal temperature variability when compared with Napa Valley (California). Since 1980, the season-to-season variability in Michigan has increased at a more rapid pace. The impacts of the increasing GDD have been positive for fruit quality, with a strong positive correlation between seasonal GDD and fruit maturation, indexed as total soluble solids (Brix). The growing season has also increased by 28 days in length since 1971. However, despite warmer temperatures, the number of days of potential frost and their seasonal variability in southwestern Michigan have remain unchanged, which continues to pose a risk for grapegrowers in the region. While it has become warmer in Michigan, and the spring warm-up is typically arriving earlier in the year, the number of days with damaging frost still has a profound impact on overall climate-related risk for grape production.

Grapevine Crown Gall Suppression Using Biological Control and Genetic Engineering: A Review of Recent Research

Crown gall is a devastating grapevine disease often encountered in vineyards prone to winter cold injury. Agrobacterium vitis, the predominant causal agent of this disease, moves from the roots via xylem sap flow to freeze injury sites where genetic transformations then occur. Crown gall disrupts the grapevine trunk vascular system, which prevents nutrient flow and leads to plant decline and death. Viticultural practices designed to fight this disease are only partially effective, thereby requiring alternatives. Genetic engineering and biological control could be more desirable approaches for disease prevention. Biological control typically involves antagonistic organisms, which are applied to grapevine roots to reduce the concentration of pathogenic Agrobacterium strains. Genetic engineering may prevent infection and tumor formation by modifying grapevines and antagonistic organisms. In the grapevine, this may be achieved by enhancing molecular mechanisms for producing bacterium-specific antimicrobial peptides or preventing transferred deoxyribonucleic acid export, integration, and oncogene expression. Alteration of antagonistic organisms enhances the production of bacteriocins effective against agrobacteria. This article reviews the potential use of biological control options and genetic engineering tools for grapevine crown gall suppression and makes recommendations for further use and research.

Impact of Crop Control Strategies on Performance of High-Yielding Sangiovese Grapevines

Climate change will require grapegrowers to develop improved viticultural practices to control vine yield and the rate of fruit maturation. The impacts of five canopy management regimens on vegetative growth, yield, and grape quality were investigated over three years, and carryover effects on vines in the fourth year were examined. Winter pruning (Wp, the control), shoot thinning (St), shoot thinning with preanthesis defoliation (St+Dpa), shoot thinning with preveraison defoliation (St+Dpv), and shoot thinning with preveraison defoliation plus cluster thinning (St+Dpv+Ct) were applied to Sangiovese vines from 2011 to 2013. Neither St nor St+Dpv changed yield or grape quality compared to Wp. The St+Dpa treatment reduced leaf area and yield by 33% compared to Wp and St and led to increased sugar concentrations and a carryover effect into 2014 that reduced vine capacity. A management strategy that combines shoot thinning with preanthesis defoliation, which will increase sugar concentrations and suppress yield, offers the strongest potential for long-term regulation of vine yield and grape quality. However, in a nonirrigated vineyard of medium vigor, Wp, St, and St+Dpv could be used to achieve yield and fruit quality levels that meet defined thresholds while reducing costs in respect to other additional interventions such as Dpa or Ct.

Double-Pruning Grapevines as a Management Tool to Delay Berry Ripening and Control Yield

Sangiovese vines mechanically spur-pruned during dormancy in February were manually finished either immediately or post budburst to test the potential of a ‘double-pruning’ approach to delay fruit sugar accumulation and limit yield. The treatments were applied in 2014, 2015, and 2016 at BBCH-0 as standard hand-finishing on dormant buds (SHF), and as late (LHF) and very late (VLHF) hand-finishing at BBCH-14 and BBCH-19, i.e., when the two apical shoots on the mechanically-shortened canes were ~10 and 20 cm long, respectively. While yield per vine was drastically reduced in the VLHF treatment (−43% versus SHF) due to high incidence of unsprouted (blind) nodes, lower shoot fruitfulness, and berries per cluster, yield reduction in LHF was −22% versus SHF due only to the incidence of unsprouted nodes. While the fruit ripening profile was not significantly modified in VLHF compared to SHF, in data pooled over three seasons, LHF delayed basic fruit composition at harvest, producing fruit with less total soluble solids, lower pH, and greater acidity, but more phenolics than SHF. Overall, LHF proved to be effective at reducing yield per vine to a level that did not require expensive cluster thinning. By reducing berry sugar accumulation, it has the potential to produce wines with lower alcohol and higher phenol content. Noteworthy too is its potential to delay harvest date or increase crop hanging time under specific vineyard conditions.

Leaf Removal and Cluster Thinning Efficiencies Are Highly Modulated by Environmental Conditions in Cool Climate Viticulture

One of several challenges in cool climate viticulture with a short growing season is to consistently reach a uniform, optimal fruit technological maturity at harvest before the first autumn frost. Weather conditions in Michigan from veraison to harvest are highly variable and unpredictable among years, constraining the preharvest assessment of fruit quality for grapegrowers and wineries. Under these environmental conditions, cluster thinning and leaf removal are commonly adopted viticultural techniques to enhance fruit ripening. Cluster thinning consists of a selective elimination of clusters to optimize the source/sink ratio of the vine. Cluster zone leaf removal induces changes in the fruit microenvironment, particularly solar radiation, temperature, and aeration. In this work, we evaluated the effects of cluster thinning and cluster zone leaf removal, applied separately in combination at veraison, on Cabernet franc in two consecutive years, 2011 and 2012. The two seasons had very distinct weather patterns from veraison to harvest. Fruit maturity was enhanced at 15 to 20 days after veraison in both years by these viticultural techniques, but with very different dynamics. The combination of leaf removal and cluster thinning led to greater fruit uniformity and better chemical composition at harvest in 2011, a year characterized by low heat accumulation after veraison. In 2012, when heat accumulation and mean temperatures after veraison were higher than in 2011, no differences were observed among treatments.

Effects of a warming trend on cool climate viticulture in Michigan, USA

Historically, Michigan’s climate had mainly three challenges for grape production: growing season temperatures were too low, the growing season was too short and there was too much rain near harvest. However, climate change in the past decades has led to a vastly different landscape that is evolving to meet the new climate. Recently, there has been a significant move from Vitis labrusca (North American) grape plantings to Vitis vinifera (wine grapes) as a consequence of Michigan’s shifting climate. The goal of this study was to analyze the historical shift in climate and its potential future impact on the grape industry. We obtained data climate model projection data from two greenhouse gas (GHG) emission scenarios. First, a multi-linear regression model was built to predict future grape yields (t/ac) using data from the climate model projections. Second, trends in the severity of the three challenges (temperature, season length, precipitation timing) were analyzed. In both GHG scenarios grape yields are seen to improve, but to different extents. The improvement is likely a response to warmer season temperatures canceling out losses to early season frost. Model projections recommend that Michigan’s future climate will be more accommodating for all varieties of grapes. This suggests that grape production will continue to grow, but the landscape will continue to evolve with more emphasis on varieties that are more climatically sensitive to cold temperatures. Climate change has greatly affected Michigan’s viticultural landscape, and will continue to do so in the coming decades.

Interannual Effects of Early Season Growing Degree Day Accumulation and Frost in the Cool Climate Viticulture of Michigan

Michigan daily climatic data and seasonal vine performance and phenological data (budburst timing) were analyzed to establish relationships between temperature (e.g., growing degree days or GDD) and juice grape yield and quality in Vitis labrusca grapevines. In viticultural regions such as Michigan, early season vine growth is highly important: Vines coming out of their winter dormancy need to withstand any potential bud-killing frosts after budburst. The temperatures during the months of March, April, and May are highly variable from year to year in Michigan, however. The average GDD accumulation at the time of budburst (average date is 27 April) from 1971 to 2011 was 158 (base 10°C) with a coefficient of variation of 45 percent. Seasonal GDD deficit or surplus at the midpoint of a growing season (as compared to an average year) was correlated to grapevine performance and the accumulation of GDD on a yearly basis was found to occur at a highly variable rate. Early season GDD accumulation was found to be a relative indicator of the end season total, where an early season deficit (or surplus) was able to predict whether the season would still be in deficit (or surplus) at the end of 80.5 percent of all seasons studied. Finally, a statistical model based on historical temperature data was created to calculate the date of budburst. Michigans warming trend will likely continue in the future, which should bring positive effects to the region. Early season variability and post-budburst frosts are likely to still be a concern in the near future, however.

Impact of Training System and Pruning Severity on Yield, Fruit Composition, and Vegetative Growth of ‘Niagara’ Grapevines in Michigan

‘Niagara’ (Vitis labruscana Bailey) vines were evaluated for 4 years, from 2000 to 2003 in a commercial vineyard in Scottdale, MI. Vines were trained as Hudson River Umbrella (HRU), umbrella Kniffen (UK), and Hybrid (HYB) and pruned for 4 years at four pruning levels (20, 40, 80, or 120 nodes/vine) and minimally pruned or hedge pruned mechanically. Node levels above 80 nodes decreased several yield components, such as cluster and berry weight. Reduction in yield and sugar components was obtained with pruning levels above 80 nodes per vine and related to a decrease in cluster and berry weight as well as a decrease in bud fruitfulness (productivity index). As number of nodes retained increased, vine size, cluster weight, berry weight, percent soluble solids, and pH decreased, while yield, cluster number, and leaf area at veraison increased. Yield components, vine size, and productivity were optimum at 20 and 40 nodes retained, but these node levels produce unacceptable low yields for economically viable juice grape production in Michigan. Therefore, retaining 80 fixed nodes produced sustainable production, without compromising vine health or long-term vineyard sustainability. There were no differences between HRU, UK, and HYB on vegetative or reproductive parameters or on fruit composition. Thus, the choice of training system—HRU, UK, or HYB—should be based on specific grower and vineyard needs.