Variation in Shiraz berry size originates before fruitset but harvest is a point of resynchronisation for berry development after flowering

Background and Aims:  Asynchronous berry development results in variation in berry size and berry composition. Variation in berry size affects vineyard yield, wine quantity and berry composition, while variation in berry composition affects fruit flavour and wine quality. The objective of this study is to identify when variation in berry size begins.
Methods and Results:  Shiraz bunches were sampled at seven stages throughout the growing season and the development of individual berries was characterised by measurements of weight, volume, surface area, deformability, seed number and seed weight. Coefficients of variation with respect to berry weight, volume and surface area were elevated throughout the post-flowering period but declined as the berries approached harvest ripeness.
Conclusions:  Variation in berry size originates prior to berry set, most probably during differentiation in the floral primordium at budburst. Harvest represents a point of resynchronisation in berry development when a number of physiological changes become synchronised between berries and within the bunch.
Significance of the Study:  Variation in berry size is presumed by the wine industry to have a negative impact on crop level, fruit composition and wine quality. Much of this presumption is scientifically unsubstantiated. The findings of this paper should encourage grapegrowers and winemakers to modify the timing of the harvest to coincide with a reduction in variation in berry size.     

The relationship between the expression of abscisic acid biosynthesis genes, accumulation of abscisic acid and the promotion of Vitis vinifera L. berry ripening by abscisic acid

Background and Aims:  Grapevines ( Vitis vinifera L.) are considered to have non-climacteric fruit, but the trigger initiating ripening (veraison) is poorly understood. This study aimed to further investigate the role of abscisic acid (ABA) during berry ripening.
Methods and Results:  In field-grown grapes over three seasons, free ABA levels increased at veraison then subsequently declined to low levels. Bound ABA increased as the free ABA level decreased after 10–11 weeks post-flowering (wpf), but ABA must also be degraded and/or exported. The absence of a large pool of bound ABA before veraison makes it unlikely that the increase in free ABA is due to the mobilization of conjugated ABA. The expression pattern of genes crucial for ABA synthesis, zeaxanthin epoxidase and two 9-cis-epoxycartenoid dioxygenases (NCEDs) indicates that berries may have the potential to synthesize ABA in situ . However, the expression profile of these genes did not correlate well with ABA levels indicating that ABA accumulation is under more complex control. The application of (+)-ABA advanced ripening as measured by colour formation, berry size increase and to a lesser extent sugar accumulation and altered the expression of one of the NCED genes.
Conclusions:  The changes in berry ABA levels around the time of veraison, which influence the timing of ripening, are under complex developmental control.
Significance of the Study:  The improved understanding of the control of berry ripening is vital to attempts to successfully manipulate this process.     

Shiraz berry size in relation to seed number and implications for juice and wine composition

This study was conducted over three seasons on irrigated Shiraz grapevines growing in a warm climate. We addressed the question of whether differences in berry size (within a population of berries from minimally pruned, own‐rooted or Ramsey‐grafted vines), would lead to differences in juice composition, wine composition or wine sensory score. Predictably, berry mass was found to increase with seed number, but berries in the smallest mass categories (0.3–0.7 g) still had similar juice soluble solids and pH; and similar concentrations of K+, tartaric acid and malic acid, compared with larger berries (1.4–2.0 g). Only for the very smallest mass category (0.3–0.55 g) was there any indication of better colour density (both for own‐rooted and Ramsey‐grafted vines) or higher anthocyanin concentration (for own‐rooted vines) compared with larger berries (1.4–2.0 g). Concentrations of tartaric acid and K+ in berry skins were highest in the smallest berry mass categories (0.3–0.7 g) and decreased with increasing berry mass (up to 1.4–2.0 g). A strong correlation (R²= 0.85) between skin tartaric acid and K+ concentrations was observed across that range. Small‐scale wine lots based on small berries (0.8–0.9 g) versus large berries (1.2–1.3 g) showed no differences in measures such as soluble solids, total acids or pH of juice; nor any differences in pH, total acids, K+, tartrate, malate, spectral characteristics or sensory score of corresponding wines. Moreover, small berries had a similar skin to fruit ratio, and a similar juice yield, compared to large berries. However, when measured post‐fermentation, the ratio of seed weight to skin weight was higher for small berries. The mass range of berries used here for small‐scale winemaking (i.e. from 0.8–0.9 g up to 1.2–1.3 g), covered the range of Shiraz berry mass typically found in irrigated vineyards (from 0.8 to 1.5 g), and thus confirms the relevance of present outcomes to practical winemaking. Finally, our data for variation in juice and wine composition as a function of berry size, showed consistent trends for all seasons, and thus implies that reported instances of improved wine quality from small berries (often associated with certain pruning treatments or deficit irrigation strategies), are more likely due to treatment effects that lead to small fruit, rather than to intrinsic developmental differences between large and small berries.     

Susceptibility of 44 grapevine (Vitis vinifera L.) varieties to downy mildew in the field

Background and Aims: Downy mildew, which occurs worldwide, is one of the most destructive of all grapevine diseases. Several authors have examined the host–pathogen interaction in different Vitis species, crosses and hybrids, but only a few studies comparing this in true V. vinifera varieties have been undertaken. The aim of the present study was to examine the in‐field susceptibility to infection by Plasmopara viticola, the causal agent of downy mildew, of 44 grapevine varieties, all belonging to the collection of the Misión Biológica de Galicia. Methods and Results: Over a period of 2 years, the incidence and severity of downy mildew on the leaves and clusters of all 44 varieties was determined using a visual scale. Some of those examined showed high susceptibility (Chenin Blanc, Albariño and Prieto Picudo), others showed low susceptibility (Silveiriña, Caiño Bravo, Follajeiro and Brancellao Blanco), and still others showed intermediate susceptibility. Some varieties showed high disease incidence but low disease severity and vice versa. No significant correlation was detected between disease incidence and severity in either leaves or clusters, nor indeed between leaves and clusters. Neither berry colour, cluster compactness nor any other studied variable bore any clear relationship with susceptibility. Conclusion: The different grapevine varieties examined showed great variation in terms of their susceptibility to downy mildew. The susceptibility of most varieties was the same in both study years. Significance of the Study: The results of this work could help provide new material that might be of use in grapevine genetic improvement programs, and in the study of resistance to downy mildew. The selection of old varieties from the Iberian northwest may contribute towards the growth of organic viticulture in this area and even other winemaking regions around the world.     

Multiple glucosyltransferase activities in the grapevine Vitis vinifera L.

The conjugation by glycosyltransferases of sugars to primary and secondary metabolites is widespread among plants and almost certainly a prerequisite for the accumulation of secondary metabolites at high levels. In the case of the grapevine, Vitis vinifera , modulating the levels of specific secondary berry metabolites is a desirable outcome for the development of wines with particular style characteristics. This can be achieved only by a thorough understanding of the processes underlying glucoside formation and accumulation during berry development. Using protein extracts prepared from leaves and berries of Vitis vinifera cvs, we show here that glucosyltransferase activities can be detected against a wide range of substrates. Among the substrates glucosylated were several classes of phenylpropanoids, including flavonols, anthocyanidins, flavanones, flavones, isoflavones, and a stilbene. Additionally, simple phenols and monoterpenes were glucosylated. Total soluble leaf proteins subjected to ion-exchange chromatography separated into fractions with differing glucosyltransferase activities. This provided strong evidence for the existence both of multiple distinct enzyme activities, and multiple isozymes catalysing identical reactions. Polyclonal antiserum raised to a V. vinifera UDP-glucose:anthocyanidin glucosyltransferase was used to demonstrate the existence of multiple glucosyltransferases in berries and leaves of the grapevine cvs Muscat of Alexandria and Shiraz, thereby confirming data obtained previously through biochemical analyses of recombinant glucosyltransferase.     

ABA during reproductive development in non-irrigated grapevines (Vitis vinifera L. cv. Tempranillo)

In grapevines, stomatal aperture decreases after a mid-morning peak during summer days. Afternoon stomatal closure increases in non-irrigated plants as water limitation progresses, which suggests the involvement of abscisic acid (ABA) in the control of stomatal aperture. The objective of this work was to study the seasonal and diurnal time-courses of CO₂ assimilation rate, leaf conductance, leaf water potential +, and ABA concentration in xylem sap, leaves, flowers and berries in non-irrigated field-grown Tempranillo grapevines throughout reproductive development. Leaf decreased throughout fruit development because water availability decreased towards the end of the reproductive cycle. CO₂ assimilation rate, leaf conductance and xylem ABA concentration also decreased during the course of the growing season. Combining all measurements xylem ABA was either not correlated, or only slightly correlated, with leaf water status + and daily leaf conductance, respectively. This lack of relationship indicates that xylem ABA during fruit ripening had functions other than provision of a non-hydraulic signal. On a seasonal basis, xylem ABA concentration measured in non-irrigated grapevines was well related to berry ABA concentration, especially at the end of fruit development (veraison and harvest).     

Effects of pre-bloom leaf removal on growth of berry tissues and must composition in two red Vitis vinifera L. cultivars

Background and Aims:  Little work has been conducted on the effects that summer pruning operations have on the relative growth of grapevine berry parts. Our paper studies whether pre-bloom leaf removal is able to modify the proportions of seed, skin and flesh in ripe grapevines berries and the related effects on must composition.
Methods and Results:  Pre-bloom defoliation (D) of the first six basal leaves on main shoots was applied to the field-grown cvs Barbera and Lambrusco salamino ( Vitis vinifera L.) in Italy's Po Valley and compared with non-defoliated controls. D showed reduced fruitset, hence yield per shoot, and concurrently improved must soluble solids and total anthocyanins in both cultivars as a likely result of increased leaf-to-fruit ratio (+3.4 cm²/g and +5.2 cm²/g for Barbera and Lambrusco, respectively) and improved relative skin mass (from 6.0 to 9.0% in Barbera and from 8.1 to 10.4% in Lambrusco). In both cultivars, skin and seed mass were highly correlated with total berry mass and changes in relative skin mass were generally not related to berry size.
Conclusions:  These results indicate that berry size per se is not the primary factor in determining final grape composition, which instead seems to depend upon factors differentially affecting the growth of the various berry components.
Significance of the Study:  Pre-bloom D induced a consistent, site and cultivar-independent increase in relative skin mass suggesting this effect being strongly physiologically regulated.     

Review: the interaction between rootstocks and cultivars (Vitis vinifera L.) to enhance drought tolerance in grapevine

Water scarcity is a key limiting factor in agriculture. Grapevines react at the physiological, biochemical and genetic level to tolerate water constraints. Even though grapevines are considered relatively tolerant to water deficits, grapevine growth and yield can be seriously reduced under water deficit. Drought‐tolerant rootstocks are expected to enable the scion to grow and yield when water supply is limited. Genetic machinery allows rootstocks to control water extraction capacity and scion transpiration. Numerous works have demonstrated the positive role of drought‐tolerant rootstocks on the control of cultivar's leaf stomatal conductance and therefore on canopy transpiration. The mechanisms, in terms of signalisation and gene functioning, need further study. Furthermore, there is no standardised methodology to rank rootstocks in terms of their tolerance to drought. A potential effect of rootstocks on stomatal development is also discussed. This review will critically discuss the current knowledge of the mechanisms of drought tolerance afforded by rootstocks, taking into account the scion/rootstock interaction, and will present some of the challenges for future investigations.     

Stomatal density of grapevine leaves (Vitis vinifera L.) responds to soil temperature and atmospheric carbon dioxide

Background and Aims: Leaf stomatal density, i.e. number of stomata per unit area of leaf, is a primary determinant of the carbon and water relations of plants. However, little is known about the plasticity of grapevine stomatal density during leaf formation in response to environmental factors. In this study, we determined responses in stomatal density to soil temperature and atmospheric carbon dioxide during leaf development following dormancy to gain further understanding of grapevine carbon and water relations, and adaptation to climate change. Methods and Results: Using potted plants of Vitis vinifera (L.) cv. Chardonnay, we found that a period of soil warming from budbreak reduced stomatal density of concurrently formed leaves, whereas CO₂ depletion increased it. Furthermore, stomatal density of concurrently formed leaves was closely and inversely correlated with starch concentration in roots and trunks. Conclusion: We conclude that the stomatal density of grapevine leaves varies greatly in response to soil temperature and atmospheric CO₂ concentration. Significance of the Study: This is the first study to show that soil temperature influences stomatal density of plants. It also confirms that stomatal density of grapevines, like many other plants, responds inversely to atmospheric CO₂ concentration. Our findings demonstrate that stomatal density must be accounted for in any attempt to predict grapevine adaptation to climate change, and attendant impacts on CO₂ assimilation and water use efficiency in viticulture. More fundamentally, they indicate that the carbohydrate reserve status of perennial, deciduous plant species may be an important endogenous determinant of stomatal density.