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.

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Gradients were observed in xylem sap ABA and in stomatal conductance along canes of Vitis vinifera L. cv. Shiraz. To investigate the source of the ABA responsible for these gradients a series of girdling and decapitation experiments were carried out. Leaf stomatal conductance and bulk ABA of leaves and apices were measured in control plants and in response to apex removal or girdling. Gradients in leaf ABA were observed over the first eight expanded leaves of field-grown Shiraz, with higher concentrations of ABA observed towards the apex. Gradients in stomatal conductance that correlated negatively with the concentration of ABA in the leaf ([ABA]leaf) were also observed over the first eight leaves. No significant effect of decapitation was observed on either leaf ABA or stomatal conductance except for the leaf immediately below the apex where a transient increase in [ABA]leaf was observed after 24 h with no corresponding decrease in conductance. Girdling resulted in an increase in [ABA]leaf in leaves distal to the girdle without the corresponding effect on conductance. These effects were further studied at the level of gene activity. To facilitate this, gene sequences encoding two key enzymes involved in the biosynthetic pathway of ABA in grape, zeaxanthin epoxidase (Zep) and 9-cis-epoxycarotenoid dioxygenase (NCED), were isolated and characterised. The cDNA sequences were used as probes to measure the abundances of their respective mRNAs in the leaf and apical material. Levels of expression of one of the two genes encoding NCED, VvNCED1, reflected the gradients in [ABA]leaf in control vines, however treatment-induced changes in ABA were not always associated with corresponding changes in VvNCED1 expression. The abundances of both the VvNCED2 mRNA and Zep mRNA increased with increasing leaf age and did not appear to be associated with either the [ABA]leaf or the expression of VvNCED1. Our results indicate that observed gradients in g s are correlated with [ABA] gradients in mature leaves and xylem sap and that these [ABA] gradients are not derived directly from the apical tissues but, at least partially, from local synthesis.

We tested the hypotheses that (i) a short period of high maximum temperature disrupts gas exchange and arrests berry growth and sugar accumulation in irrigated Shiraz vines (Vitis vinifera L.), and (ii) the magnitude of these effects depend on the phenological window when stress occur. Using a system combining passive heating (greenhouse effect) and active cooling (fans) to control daytime temperature, we compared vines heated to a nominal maximum of 40°C for three consecutive days and untreated controls. Maximum air temperature in heated treatments was 7.3°C (2006–07) and 6.5°C (2007–08) above ambient. Heat episodes were aligned with the beginning of a weekly irrigation cycle and applied in one of four phenological windows, namely post-fruit set, pre-veraison, veraison and pre-harvest. Heating systems did not affect relative humidity, hence vapour pressure deficit (VPD) was increased in the heated treatments and tracked the daily cycle of temperature. Heat did not affect the dynamics of berry growth and sugar accumulation, except for a 16% reduction in berry size and sugar content in vines heated shortly after fruit set in 2006–07. Vines upregulated stomatal conductance and gas exchange in response to heat. Stomatal conductance, photosynthesis and transpiration at a common VPD were consistently higher in heated vines than in controls. We suggest that stomatal behaviour previously described as part of Shiraz anisohydric syndrome may be adaptive in terms of heat tolerance at the expense of short-term transpiration efficiency.

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Improvements in the efficiency of water use in Australian vineyards have included a move away from diffuse or ‘total cover’ irrigation techniques to drip irrigation systems. This change in irrigation method has a significant effect on moisture distribution within the soil profile, with implications for root growth, root‐system architecture, and soil‐water acquisition. Those issues are addressed in this paper. Our report is based on grapevines that had been established under a diffuse irrigation system (overhead sprinklers or microjets) and subsequently converted to drippers. Results are also presented to show the influence of soils with different water holding capacities on root distribution within a single vineyard. Variations in soil texture within a vineyard were found to influence the vertical distribution of roots, whereas irrigation history had more influence on horizontal variations in root density within a depth range. Conversion of vines from sprinkler irrigation to drippers resulted in a marked increase in total root mass (volume) under the drip line, particularly 25–50 cm below the surface. Roots were differentially influenced by irrigation history according to their diameter class. Under drip irrigation, the largest increase in root‐length density occurred with roots in diameter classes between 1 and 4 mm diameter. Grapevines established under sprinklers, and subsequently converted to drip irrigation, had significantly larger root systems (within the volume of soil sampled) than did vines maintained under sprinklers throughout. Therefore, vines established under sprinkler irrigation and then converted to drippers may be better equipped to cope with deficit irrigation during drought (via either RDI or PRD), by virtue of those additional roots.

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Background and Aims:  We modelled the dynamics of soluble solids, largely sugars, and water in 12 Vitis vinifera varieties. Emphasis was placed on maximum concentration of soluble solids (Smax) and time of maturity for their viticultural importance. Methods and Results:  We measured the concentration of soluble solids and water at weekly intervals during berry ripening. The dynamics of concentration of soluble solids was characterised with a sigmoid model, whereas water concentration was characterised with a concentration–response type curve. Scaling exponents for soluble solids (αs) and water (αw) were calculated as the slope of the log–log regression between amount of soluble solids or water per berry and berry fresh mass. Smax ranged from 27.1% in Shiraz to 21.2% in Riesling, was associated with both αw and αs, and was largely unrelated to source size (leaf area, pruning weight, light interception), source activity (stomatal conductance), sink size (yield components) and source : sink ratios. The time of maturity ranged from 26 January in Verdelho to 27 February in Crimson Seedless, and was an inverse function of the rate of change in concentration of soluble solids, which was in turn a direct function of stomatal conductance. Conclusions:  Traits related to carbon assimilation influenced time of maturity, but their link with maximum concentration of soluble solids in berries was not evident. Significance of the Study:  Quantitative models of accumulation of soluble solids are presented that provide a baseline for comparisons among varieties.