Suitability of pre‐dawn and stem water potential as indicators of vineyard water status in cv. Tempranillo

Background and Aims: Irrigation management requires the collection of up‐to‐date information that allow growers to make rapid decisions, water potential being one of the most used parameters in irrigation scheduling. The goal of this research was to determine whether predawn (Ψpd) and stem (Ψs) water potential can be used equally well, quantifying the effect external factors have on the relationship between them. Methods and Results: Ψpd, mid‐morning (Ψs‐m) and noon (Ψs‐n) stem water potential were measured at seven cv. Tempranillo vineyards. Climatic conditions, vine growth and fruit load affected daily water potential dynamics. A greater decline of Ψs occurred when temperatures were higher and there was no dew formation, as well as under larger canopies and fruit load. While the relative impact of these variables on water potential was not particularly high, it was by no means negligible. Conclusions: Data collected in this study did not favour Ψpd, Ψs‐m or Ψs‐n as a preferred measure to evaluate plant water status. It is important to remark that similar Ψpd values do not necessarily indicate the same level of deficit, and that similar Ψs values do not always mean similar water availability. Therefore, a straightforward interpretation of Ψpd and Ψs can sometimes be misleading. Significance of the Study: The results obtained provide significant explanation to the lack of agreement in the literature regarding the most suitable time to measure water potential. Vineyard managers and scientists should select it according to the level of stress expected, climatic conditions and irrigation frequency.     

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.     

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.     

Effects of nutrient and water stress on vegetative and reproductive growth in Vitis vinifera L.

Two watering and two nutrient regimes were applied to small vines established in pots and grown under greenhouse conditions. With water, a comparison was made between water adequacy (WH) and intermittent water stress (WL); with nutrition, between nutrient sufficiency (NH) using fertiliser-enhanced potting medium and insufficiency (NL) with one-fifth fertiliser application. NL reduced major growth parameters - shoot length, stem weight and leaf weight - more than did WL. Both NL and WL reduced node and leaf number, but only NL reduced internode length, leaf area and weight. WL had bigger effects when combined with NH than with NL. WL, especially when combined with NH, advanced maturity by ten days. Effects of W and N on pH, malic acid, tartaric acid and total soluble solids (°Brix) were different. The °Brix values were similar in WH and WL, but were less in NH than in NL. The treatments interacted in pH, malate and tartrate: pH was highest in WL/NH and lowest in WH/NH; malate tended to be less at both WL and NL, while tartrate concentration tended to become smaller from WH to WN but greater from NL to NH. No significant changes in the levels of citric acid, anthocyanin or reducing sugars were observed as a consequence of any treatment. Thus, although levels of stress due to WL or NL may have been different, the differences in the effects on several variables indicate that there is no general response to stress but that responses vary according to the factor inducing the stress. The level of reduction in variables measuring vegetative growth was 2– to 3-fold greater than induced changes in juice composition. Advancement of maturity would suggest a potential value of intermittent water stress combined with adequate nutrition in areas with short seasons. Low-nutrient soils might be desirable in areas where other factors are likely to induce strong growth.     

Grapevine growth of shoots and fruit linearly correlate with water stress indices based on root-weighted soil matric potential

Over two consecutive seasons, six deficit irrigation regimes were imposed on Colombard vines on Ramsey rootstock. The soil water availability was quantified by logarithmic transformation of the absolute value of a root-weighted measure of soil matric potential. Stem water potential declined linearly with decreasing soil water availability. Water stress indices were calculated by integrating the daily values of soil water availability over specific periods. Declines in both fruit and vegetative growth were linearly correlated with increases in the values of water stress indices during the respective growth periods. In the berries, concentrations of total soluble solids, tartrate and potassium were not correlated with the water stress index during the period of fruit growth; malate concentration declined linearly with increasing values of this index. Responses of pH and titratable acidity to variation in the water stress index were not consistent in the two seasons.