Long-term Weather Observations Reveal the Impact of Heatwaves on the Yield and Fruit Composition of Cabernet Sauvignon

Aims: Rootstocks provide protection against soil-borne pests and are a powerful tool to manipulate growth, fruit composition and wine-quality attributes. The present study aimed to assess the consistency of rootstock effects on the growth and fruit composition of scion varieties and identify scion × rootstock interactions.Methods and results: Vine performance and fruit composition of hot-climate, drip-irrigated, spur-pruned Chardonnay, Cabernet Sauvignon and Shiraz, grafted on seven rootstocks, was assessed over five seasons from 2013 to 2017. Rootstocks included Ramsey, 1103 Paulsen and 140 Ruggeri and four promising selections from the CSIRO rootstock development programme. Vines were trained as quadrilateral cordons on a two-wire vertical trellis of height 1.8 m and 3.0 m row × 1.8 m vine spacing, and irrigated with 5.5–6.0 ML/ha of water each season. The study was conducted with mature vines, established in 2006, as a randomised block design with five replicates. There were significant effects of both variety and rootstock on yield, number of bunches, bunch weight, berry weight (scion only), berries per bunch, pruning weight and the Ravaz Index (yield/pruning weight). Despite identical management practices, there were large differences between scion varieties in key growth characteristics across rootstocks. Chardonnay produced a high yield (mean 25.2 kg/vine) with low pruning weight (2.3 kg/vine) and a high mean Ravaz Index value of 12.1. Shiraz had the highest yield (27.4 kg/vine) with high pruning weight (5.1 kg/vine) and a Ravaz Index of 6.3. Cabernet Sauvignon had the lowest yield (15.9 kg/vine) and highest pruning weight (6.6 kg/vine) and a very low Ravaz Index value of 3.0. Effects of rootstock on growth characteristics were smaller than the effects of variety, with mean yields ranging from 19.5 to 25.9 kg/vine, pruning weights ranging from 3.24 to 6.13 kg/vine and mean Ravaz Index values ranging from 5.54 to 8.63. Each variety was harvested when the mean total soluble solids reached 25.0 °Brix. Significant effects of variety and rootstock on fruit composition, included pH, titratable acidity (scion only), malate, tartrate (scion only), yeast assimilable nitrogen (YAN); and for the red varieties, total anthocyanins (scion only) and phenolic substances (scion only). Significant interactions between scion variety and rootstocks were found for yield, number of bunches, berry weight, pruning weight and Ravaz Index. The effect of rootstock on bunch weight and berries per bunch was consistent across scions. Significant scion × rootstock interactions were also found for pH and YAN. For each variety, significant effects of rootstock on fruit composition were linked to growth characteristics. However, these relationships, based on correlation analyses, varied for each scion.Conclusions: The study has shown that growth characteristics and fruit composition of the major varieties was not consistent across seven rootstock genotypes, as significant scion × rootstock interactions were determined. Hence, different rootstocks may be required for each variety to optimise scion performance and fruit composition. The study has also shown that the new CSIRO rootstock selections, covering a range of vigour classifications, may be useful alternatives to those currently in use by industry.Significance and impact of the study: The study has shown that the performance of scion varieties, and to a lesser degree the fruit composition, is dependent on rootstock choice. The inherent vigour of the scion variety must be considered in rootstock selection. Furthermore, individual scion/rootstock combinations may require specific irrigation, pruning or canopy management to achieve vine balance and optimise fruit and wine composition.

Grapevine red blotch virus (GRBV) is an important threat to vineyards in North America due to severe impacts to vine health, fruit composition, and wine quality. The goal of this study was to investigate the utility of crop thinning to mitigate the effects of GRBV in Cabernet Sauvignon in the Okanagan Valley and to determine if GRBV viral load plays a role in vine health and fruit composition. A commercial Cabernet Sauvignon vineyard was studied over 2 years. GRBV(+) and GRBV(−) vines were paired and assigned a cropping treatment of either 1.5 clusters per shoot (1.5 C/S) or one cluster per shoot (1.0 C/S). Vine health parameters, including leaf greenness, leaf gas exchange, pruning weights, and bud hardiness, were measured throughout the growing season, and fruit composition was assessed at harvest. GRBV viral load was measured at four stages during the growing season using Droplet Digital PCR (ddPCR). GRBV(+) vines had higher berry and cluster weights, yields, and crop loads, and lower pruning weights. GRBV(+) vines had drastically reduced Brix, as well as decreased yeast assimilable nitrogen, and increased titratable acidity and pH. Skin and seed phenolic profiles were unaffected by GRBV. Crop thinning decreased yields and increased pruning weights, resulting in lower crop loads. However, crop thinning had no impact on vine health or fruit composition of GRBV(+) nor GRBV(−) vines. GRBV viral load was positively correlated with skin anthocyanins, tartaric esters, flavonols, and tannins, and negatively correlated with stomatal conductance, cluster weight, yield, berry weight, and titratable acidity. GRBV significantly altered fruit composition in Cabernet Sauvignon and is not remedied by crop thinning. GRBV viral load had no clear influence on vine health and fruit composition. Due to the lack of impact of crop thinning in GRBV(−) vines, we show no benefit to thinning Cabernet Sauvignon past 1.5 C/S in the Okanagan Valley.

The objective of this work was to evaluate the effect of heat waves on the bud dormancy of grapevines with contrasting chilling requirements. ‘Chardonnay’, ‘Merlot’ and ‘Cabernet Sauvignon’ hardwood cuttings were collected in vineyards of Veranópolis, State of Rio Grande do Sul, Brazil, and were exposed to constant (7.2°C) or alternate (7.2 and 18°C for 12/12 hours) temperatures, combined with zero, one or two days a week at 25°C. Periodically, part of cuttings was transferred to 25°C for daily budburst evaluation. Endodormancy (dormancy controlled by cold) was overcome with 150 chilling hours (CH) at 7.2ºC in ‘Chardonnay’, 300 CH in ‘Merlot’ and 400 CH in ‘Cabernet Sauvignon’. Daily temperature cycles ranging from7.2ºC to 18°C did not affect the endodormancy process. Heat waves of 25°C resulted in increase in CH to overcome endodormancy. The negative effect of heat waves depended on their duration, with heat partially canceling out the chilling accumulation after 36 continuous hours on the dormancy. Such evidence shows that the dormancy evolution is affected by the impact of the heat interspersed with cold, and should be considered in the adjustment and/or development of better-adapted models for the prediction of the budburst potential of the grapevine culture in Southern Brazil.

Prohexadione-calcium (prohexadione-Ca) was applied to field-grown Cabernet franc, Cabernet Sauvignon, Chardonnay, and Seyval to evaluate rates and timing effects on fruit yield components and on fruit and wine composition. Berries per cluster, berry weight, cluster weight, and clusters per shoot in the subsequent season were all decreased by multiple, prebloom plus postbloom, applications to Cabernet Sauvignon and Cabernet franc. Similar reductions in current season components of yield were observed with Seyval. Application (250 mg/L) to single clusters of Cabernet Sauvignon and Chardonnay at bloom, or in the one-to-two-week prebloom period decreased fruit set, whereas applications one to two weeks postbloom reduced berry weight, with no impact on fruit set. Berry weight reduction correlated to increased color intensity (420 nm + 520 nm), total anthocyanins, total phenols, and phenol-free glycosyl-glucose (PFGG) in Cabernet Sauvignon. In a separate experiment, prohexadione-Ca increased Cabernet franc must color intensity, total anthocyanins, and total phenols, despite having minimal effects on berry weight or crop yield. Aroma and flavor triangle difference tests did not distinguish treatment differences with young Cabernet franc wines. This study of prohexadione-Ca effects on grape reproductive development illustrated that berry set and berry weight were responsive to application timing, with the one-to-two-week period after bloom most sensitive to reductions in berry weight. The concurrent effects on fruit composition were generally positive, while the full impact on wine quality remains equivocal, but worthy of further evaluation.

The effect of sunlight exposure on yield, fruit composition, amount of damaged clusters, and berry temperature was evaluated in a terraced, hillside `Cabernet Sauvignon' vineyard on the north coast of California. Each terrace contained two vine rows identified as “inside” and “outside” relative to the terrace surface. The standard canopy management practice of removing lateral shoots from below the clusters was imposed with three modifications (“umbrella”, “fogger”, and “umbrella+fogger”) and an unmodified control. Applications of a kaolin-based particle film were made to unmodified canopies and a final treatment consisted of leaving lateral shoots. Canopies with umbrella modifications were not fully vertically shoot positioned. Fogger emitters directed water into the cluster area when ambient temperature reached 33.9 °C beginning in mid-July for a total of 16 fogger-events through 8 Sept. 2004. Treatments were harvested 17 Sept. Yield was affected by row type but not treatment, and inside and outside rows produced an average of 2.1 and 3.4 kg/vine, respectively. Particle film applications significantly reduced berry surface temperatures in the afternoon of two measurement dates by 0.7 and 1.5 °C, respectively. Applications did not significantly affect fruit maturity indices when compared to fruit in the control; however, at the 7% probability level, berry samples from vines that had been treated with kaolin-clay had lower °Brix than samples from control vines. The mean range of sunburn fruit across all treatments was 0.2 to 1.4 clusters per vine. Umbrella and umbrella+fogger treatments significantly reduced the number of damaged clusters (P < 0.05).

SummaryThe effects of training-pruning regimes on Eutypa dieback, vigour, yield and fruit composition were evaluated in ‘Cabernet Sauvignon’ grapevines from 1991 to 2004 in Galt, California, USA. Mechanical pruning at bud swell, and minimal pruning (trimming only in Summer) gave the least dieback. In contrast, pruning of dormant vines trained on either a bilateral cordon or a Sylvoz system increased wounding and dieback. Hand pruning of head-trained vines gave fewer cuts and less dieback, compared with vines trained as bilateral cordons or Sylvoz. Dieback reduced the extension of fruiting arms on bilateral cordon- and Sylvoz-trained vines with dormant season pruning, whereas arms were healthy after mechanical and minimal pruning. Hand-pruned vines (bilateral cordon, Sylvoz or head) had greater pruning weights, fewer shoots and clusters, heavier clusters, and lower yields than vines pruned mechanically or minimally. Despite the presence of dieback, yields did not decline over 14 years (except for Sylvoz-trained vines from 2002, and bilateral cordon-trained vines from 2003). Fruit had lower °Brix and pH, and higher titratable acidity in some years, suggesting possible delays in fruit ripening on minimally-pruned vines. Mechanical pruning at bud swell and Summer trimming can minimise Eutypa dieback while maintaining yield and fruit quality. Training-pruning regimes that require early pruning and that generate large numbers of wounds when vines are dormant should be avoided where Eutypa is a concern.

Six ‘Cabernet Sauvignon’ grapevine selections from the Foundation Plant Services (FPS), UC Davis, were evaluated near Fresno, California. Selections FPS 2, 8, 10, 21, 22, and 24, were planted in April 1997 as own-rooted cuttings, and fruit yield and composition were assessed annually from 2000 through 2003. Harvested on the same dates in a given year, selections 8, 21, and 22 had higher yields than the others because they had either: heavier berries, larger clusters, more clusters, or several of these variables. Selections had similar numbers of berries per cluster. Fruit of selections 22 and 24 generally matured first and the fruit of selection 2 matured last. Each selection had similar skin anthocyanin concentrations in the one year that pigments were measured.

A trial was conducted during the 2005–2006 season in order to determine the effects of different leaf-to-fruit ratios on yield components and fruit composition in four Vitis vinifera L. cultivars. The treatments consisted of selecting shoots of four lengths (>1.3 m, 1.3–0.8 m, 0.8–0.4 m, and <0.4 m) with two crop levels (1–2 clusters/shoot), which allowed defining eight ratios. Berry composition and yield components were measured. The treatments affected the accumulation of soluble solids in “Sauvignon blanc”, “Cabernet Sauvignon”, and “Syrah”, delaying it as the ratio decreased. All yield components were affected in “Sauvignon blanc”, while bunch weight and the number of berries per bunch were altered without a clear trend. None of the yield components were affected in “Cabernet Sauvignon”, while the lowest ratio presented the lowest number of berries per bunch in “Syrah”. Total polyphenol index (TPI) was affected in “Carmenère” without a clear trend. A highly significant correlation was found between shoot length and leaf area in all studied cultivars. As the ratio increased, the shoot lignification increased in “Sauvignon blanc”. However, studies must be conducted during more seasons to establish better conclusions about the effects of leaf-to-fruit ratios on yield and fruit composition.

The cold tolerance, phenology, yield, and fruit maturity of alternative red- and white-skinned wine grape cultivars ( Vitis vinifera ) of European origin were compared with those of ‘Merlot’ and ‘Cabernet Sauvignon’ over two growing seasons in southwestern Idaho. Variability among alternative cultivars was detected for cold hardiness, onset of phenological events, yield, and fruit composition. The red-skinned cultivars Montepulciano and Tinto Cão were the least cold hardy of the alternative cultivars. The red-skinned cultivars Aleatico, Aglianico, and Graciano had similar yield but matured later than the leading cultivars Merlot and Cabernet Sauvignon and were among the more cold-sensitive alternative cultivars. ‘Grüner Veltliner’, ‘Sauvignon Gris’, and ‘Trousseau’ cold acclimated early, had high midwinter bud cold hardiness, and had similar or higher yield and fruit maturity as the leading cultivars. The white-skinned cultivars Verdelho, Fernão Pires, Sauvignon Blanc Musqué, and Sauvignon Gris had similar or less vine injury, similar or earlier phenology, and similar yield and fruit maturity as the leading cultivars. The large berry size of the red-skinned cultivars Trousseau and Touriga Brasiliera warrants evaluation for wine quality. The cultivar variability identified in this study for cold hardiness, phenology, cluster architecture, and yield provides a useful guide for cultivar site selection.

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) were evaluated separately over two years on Vitis vinifera L. variety `Cabernet Sauvignon' for their applicability to commercial vineyards in Texas and to investigate their potential for enhancing grapevine acclimation and cold hardiness. PRD treatments compared the alternating-half-rootzone water application strategy of PRD to an equal volume of water applied to the entire rootzone and a 2× volume of water applied to the entire rootzone. RDI treatments compared the effects of deficit irrigation at different developmental stages of grapevine: post-fruit set to veraison; veraison to harvest; post-harvest; and a no-deficit control. The PRD treatment plots performed similarly to the equal volume treatment plots for yield and fruit composition. The double-volume treatment had a trend to higher yield in 2002 and statistically significant higher yields in 2003, and slightly lower soluble solids content of fruit in 2002. Thus, the two deficit treatments, PRD and Equal, experienced only a small reduction in performance while enabling reduced water usage. The PRD alternating-half-rootzone strategy demonstrated no advantage over a standard deficit irrigation strategy. Grapevines irrigated with the RDI strategy responded to this treatment most during the post-fruit set to veraison stage of development, which had lower yields and higher fruit soluble solids compared to the no-deficit treatment in 2002. Both PRD and RDI deficit irrigation strategies significantly increased the earliness and rate of periderm development on shoots in both years, but did not result in consistently greater cold hardiness compared to no-deficit treatments.

The heterogeneity of berry heterogeneity is a commonly occurring phenomenon that has a big influence on fruit composition and wine quality. To clarify this relationship, ‘Cabernet Sauvignon’ grapes were collected at harvest from a single vineyard and divided into three categories in two consecutive years: small (≤ 0.75 g), medium (0.76-1.25 g), and large (> 1.25 g). The medium berries were present in the highest frequency, accounting for more than 50% of the berry populations. The standard physicochemical parameters of the fruit were significantly affected by berry size. The relative skin mass and soluble solids contents, as well as total phenolic and anthocyanin concentrations, decreased with the berry size, while the relative seed mass, pH and malic acid content were positively correlated with berry weight. Accordingly, the wine composition also varied with berry size, as the wines made from small berries showed the highest alcohol and residual sugar content. CIELab parameters of the resulting wines showed the small berries were more desirable for making wine with a deeper and more saturated colour. With regard to volatile compounds, berry size showed a limited effect. Only 1-hexanol and laevo-2,3-butanediol showed consistent and significant trends across vintages for wine volatiles, which showed the highest levels in wines made from the small category of berries.

The effects of sunlight exposure on the berry growth and composition of two red wine grape cultivars grown in the central San Joaquin Valley of California (Region V) were examined. Field grown Cabernet Sauvignon and Grenache grape clusters were grown over a range of sunlight exposures (mid-day PAR <10 µmol m^-2 sec^-1 [shaded] to >600 µmol m^-2 sec^-1 [fully exposed]) from berry set to harvest. Both cultivars were planted in east-west oriented rows, and experimental clusters were evenly distributed between the north (afternoon shaded) and south (afternoon exposed) sides of the canopy. Fruit response to sunlight varied based on cluster location within the canopy, and these results were at least partially due to measured differences in berry temperature. At the same exposure level or PAR (photosynthetically active radiation), mid-day berry temperature was generally 3 to 4°C greater for clusters on the south side of the canopy compared to clusters on the north. Soluble solids initially increased with greater sunlight exposure, then declined when mid-day PAR exceeded 31 to 50 and 51 to 100 µmol m^-2 sec^-1, respectively, for clusters on the north and south sides of the canopy. Titratable acidity generally declined as sunlight exposure increased, with Cabernet Sauvignon clusters on the north side of the canopy maintaining greater acidity at the same exposure level than clusters on the south. Juice pH declined as exposure increased on the north side of the canopy, while sunlight had little effect on juice pH for clusters on the south. Anthocyanins increased linearly as sunlight exposure on the north side of the canopy increased, but declined when cluster exposure on the south exceeded 100µmol m^-2 sec^-1. Total phenolics generally followed a similar pattern. The results suggest that the effects of light on fruit composition are heavily dependent upon the extent to which berry temperature is elevated as a result of increased sunlight exposure. Prolonged exposure of clusters to direct sunlight should be avoided for maximum berry color in the central San Joaquin Valley and other warm regions.

Deficit irrigation is used increasingly as a vigor management tool and to conserve water in grape vineyards. Several strategies including regulated deficit irrigation (RDI) have emerged, but none has been evaluated in Texas. Deficit irrigation has also been observed to influence vine acclimation and presumably vine cold hardiness. Experiments were established in a commercial ‘Cabernet Sauvignon’ (Vitis vinifera) vineyard in west Texas to evaluate RDI under local conditions and to study the potential for deficit irrigation to induce earlier shoot acclimation and influence cold hardiness. RDI significantly reduced pruning weights by as much as 46% and increased applied water-use efficiency up to 72%, but had little or no effect on yield components or fruit composition, indicating that these strategies could be useful in west Texas. Deficit irrigation was consistently associated with earlier and more rapid development of periderm on shoots, but had no effect on bud cold hardiness.

Area under wine grape cultivation is increasing in semiarid tropical regions of India. There is lack of information on role of rootstocks influencing must composition and thereby wine quality under such climatic conditions. Majority of area under table grape cultivation is grafted on Dogridge rootstock, which is also been used for wine grapes. Grapes harvested from vines grafted on Dogridge were known to possess high potassium resulting in high pH which has adverse effect on wine quality. Hence, this study was initiated to understand fruit composition and wine quality of 'Cabernet Sauvignon' grapes grafted with each of the rootstocks 101-14Mgt, 1103P, 110R, 140Ru, Fercal, Gravesac and SO4. Rootstocks significantly influenced many of the must composition parameters such as sugars, organic acids, phenolic compounds, potassium and pH. Significant and positive correlation was observed between potassium content, juice pH and malic acid. Rootstocks 101-14 Mgt and Gravesac accumulated more potassium in fruits which also had higher malic acid and juice pH, while it was least on 110R, 1103P, Fercal and SO4 rootstocks. The potassium content in juice was directly related to wine pH, wherein wines made from 'Cabernet Sauvignon' grafted on 101-14 Mgt and Gravesac had highest pH. Content of most of the phenolic compounds in must and wine were significantly influenced by rootstocks. There was more than two fold increase in the total phenolic content from must to wines with highest phenols recorded in wines made from fruits harvested on 110R rootstock.

Crop load adjustment is widely accepted as an important vineyard management tool for premium-quality wine production. However, little information is available on its effectiveness under warm, dry climatic conditions. Crop loads were altered on three own-rooted winegrape cultivars grown in a mature, deficit-irrigated vineyard in the arid Yakima Valley (Washington) over a five-year period (1997 to 2001). Thinning consisted of preferentially removing clusters on shoots not arising from nodes deliberately retained at pruning, either one month after bloom or at veraison, to achieve target yields for Cabernet Sauvignon (6.7 t/ha), Riesling (9.0 t/ha), and Chenin blanc (11.2 t/ha). Removing, on average, 39% of the clusters from Cabernet Sauvignon, 30% from Riesling, and 38% from Chenin blanc reduced yields by 36%, 17%, and 20%, respectively. Average crop loads varied from 6.7 to 14.8 kg fruit/kg pruning weight for nonthinned vines and from 4.4 to 9.2 for thinned vines, and average yields varied from 7 to 25 t/ha for nonthinned vines and from 5 to 16 t/ha for thinned vines, depending on cultivar and season. Cluster thinning and its timing had little or no influence on shoot growth, leaf area, pruning weight, berry number, berry weight, and fruit composition (soluble solids, titratable acidity, pH, color) in both the current and subsequent seasons. Differences in vegetative growth, yield formation, and fruit composition within cultivars were mostly due to season (including weather and soil moisture) rather than to yield or crop load.