Influence of trellis system and shoot positioning on light interception and distribution in two grapevine cultivars with different architectures: an original approach based on 3D canopy modelling

Background and Aims: A 3D modelling approach simulating canopy structure was used in combination with a radiative transfer model to simulate light interception, distribution and microclimate in the fruiting zone. Methods and Results: This model was parameterised for four training systems (two vertical shoot‐positioned systems with one or two pairs of catch wires (VSP‐1W, VSP‐2W); two non‐shoot‐positioned systems, gobelet (GOB) and bilateral free cordon (BFC)) and two cultivars (Syrah and Grenache). Light interception and canopy microclimate depended on the interactions between the intrinsic architecture of the cultivars and canopy manipulations. Shoot vigour and leaf area were the main determinants of canopy radiative balance. However, differences in shoot architecture accounted for up to 25% of the difference in light interception between cultivar × trellis system pairs at a given leaf area index (LAI). Light interception efficiencies and the proportion of sunlit leaf area (SLA) were 25–30% lower for VSP‐2W than for BFC for intermediate LAI values. The genotypic differences in the ability to capture light were mostly induced by the ‘procumbent’ habit of the Syrah shoots. For this cultivar, shoot‐positioned systems resulted in lower levels of fruit illumination at midday than the BFC and GOB systems, whereas the use of a catch wire in VSP‐Grenache canopies made it possible to maintain light penetration in the fruit zone. Conclusions: These results highlight the problem of adapting the training system to both the architectural characteristics of the cultivar and climate. Free‐standing systems had greater light interception and SLA than shoot‐positioned systems. They may enhance fruit illumination for cultivars with ‘procumbent’ shoots. Significance of the Study: Non‐positioned shoot systems offer the possibility of combining a high level of light interception, favourable microclimate and reduced labour‐intensive practices for vineyards in conditions of moderate vigour.     

Grape vine varieties Shiraz and Grenache differ in their stomatal response to VPD: apparent links with ABA physiology and gene expression in leaf tissue

Two cultivars of Vitis vinifera L., namely Grenache and Shiraz, have been described as having near-isohydric and near-anisohydric responses respectively to soil water stress (Schultz, Plant Cell and Environment , 26, 1393–1405, 2003). Given that contrast in sensitivity to soil water, a question arises as to whether atmospheric moisture stress will elicit similar differences. The present study was undertaken to investigate this issue by comparing stomatal responses in these same two cultivars to contrasting vapour pressure deficit (VPD). Test material included field grape vines in the Barossa Valley and pot-grown vines under partial shade in Adelaide. Our experiments showed that the same isohydric/anisohydric distinction as described by Schultz (2003) is apparent in leaf responses to atmospheric moisture stress. In the more isohydric cultivar, Grenache, stomatal conductance is more responsive to changes in VPD. This heightened sensitivity (compared with Shiraz) appears to be associated with higher levels of abscisic acid (ABA) in Grenache xylem sap. Expression studies on the key genes in the ABA biosynthetic pathway indicate that regulation of the V.v . nced1 gene expression in leaf tissue, but not in the root tissues, is associated with the changes in the xylem sap ABA. Moreover, the two cultivars (Grenache and Shiraz) differed with respect to both scale and time course of those responses. We conclude that these two Vitis vinifera cultivars do indeed differ significantly in the way that they respond to potentially stressful atmospheric conditions, and that ABA physiology is a key process in these contrasting responses. An understanding of such mechanisms, including the relative importance of roots and shoots in determining vine response to abiotic stress, is highly relevant to irrigation scheduling, and to management of associated variation in vineyard productivity across diverse environments.     

The aroma of Grenache red wine: hierarchy and nature of its main odorants

A young Grenache red wine from 1995 harvest was continuously extracted with Freon-11 and the extract cleaned up with aqueous NaHCO₃ in order to remove fatty acids. An Aroma Extract Dilution Analysis was carried out with that extract in a Carbowax 20M capillary column with simultaneous MS and olfactometric detections. The AEDA analysis showed that there are 43 flavour active regions in the chromatogram whose aromatic intensities ranged from less than 16 to more than 1000 arbitrary flavour dilution coefficients. To isolate the odorants, the extract was further washed with propylglycol, concentrated, and then fractionated by normal phase HPLC with UV detection at 220 nm in order to obtain 29 fractions. All the fractions were concentrated and analysed in the same HRGC-MS-olfactometric system in which the AEDA experiment was performed. The strategy allowed to isolate most of the odorants, and 30 of them, among which were the most important, could be clearly identified. Some others could not be identified but their mass spectra are given. Among the most important odorants there are some well known fermentation esters but, surprisingly, the role played by some minor esters, such as the ethyl esters of isobutyric, isovaleric and 2-methylbutyric acids, seems to be very important. Equally important could be the role played by some volatile phenols, terpenols, lactones and some nor-isoprenoids. © 1998 SCI.     

Effects of mechanical thinning on fruit and wine composition and sensory attributes of Grenache and Tempranillo varieties (Vitis vinifera L.)

Background and Aims: Cost-effective yield control is required by the wine industry in order to reduce the existing worldwide wine surplus and to improve grape quality. The object of this study was to evaluate the chemical and sensory effects on the resulting wines of mechanical cluster thinning performed at different intensities on Grenache, and at different timings (pea size and veraison) on Tempranillo. Methods and Results: The experiments were conducted with a machine harvester in 2007 on two commercial vertical shoot-positioned vineyards in Spain's Rioja region. In both varieties, mechanical thinning was effective in yield reduction and resulted in more ripened fruit, and wines with higher alcohol and pH values, more intense colour and increased phenolic content. Regardless of the thinning intensity, sensory changes were less noticeable in Grenache than in Tempranillo wines. Of the latter, those from vines thinned during veraison were less aromatic and sour, but had increased astringency. Conclusions: Yield management through mechanical thinning induced changes to the chemical composition of fruit and wines as well as to the wines' aroma, taste and mouthfeel. The extent of the sensory implications seems to depend on several factors such as the variety and timing of thinning application. Significance of the Study: This is one of the first studies addressing the effects of mechanical thinning on the sensory properties of the resulting wine and has implications for viticultural management practices.