E. W. R. Barlow

Partial rootzone drying and deficit irrigation increase stomatal sensitivity to vapour pressure deficit in anisohydric grapevines

The aim of this study was to investigate how alternative irrigation strategies affected grapevine (Vitis vinifera L.) stomatal response to atmospheric vapour pressure deficit (VPD). In two sites, application of partial rootzone drying (PRD) at 90–100% of crop evapotranspiration (ETc) increased stomatal sensitivity of Shiraz (Syrah) grapevines to high VPD compared with control vines irrigated with the same amount of water but applied on both sides of the vine. PRD significantly reduced vine water use (ESF) measured as sap flow and in dry conditions increased the depth of water uptake from the soil profile. In both experiments, PRD reduced vine water use by up to 50% at moderate VPD (~3 kPa) compared with control vines irrigated at the same level. In the same vines, the response to PRD applied at 100% ETc and deficit irrigation applied at 65% ETc was the same, increasing stomatal sensitivity to VPD and decreasing sap flow. Hydraulic signalling apparently did not play a role in changing stomatal sensitivity as there was no difference in stem water potentials between any of the treatment (PRD and DI) and control vines. This suggests that a long distance root-based chemical signal such as ABA may be responsible for the changes in stomatal behaviour. Shiraz grapevines have previously been classified as anisohydric-like, but application of PRD and DI increased stomatal closure in response to conditions of high evaporative demand making the vines behave in a more isohydric-like manner.

Impact of future warming on winter chilling in Australia

Increases in temperature as a result of anthropogenically generated greenhouse gas (GHG) emissions are likely to impact key aspects of horticultural production. The potential effect of higher temperatures on fruit and nut trees’ ability to break winter dormancy, which requires exposure to winter chilling temperatures, was considered. Three chill models (the 0–7.2°C, Modified Utah, and Dynamic models) were used to investigate changes in chill accumulation at 13 sites across Australia according to localised temperature change related to 1, 2 and 3°C increases in global average temperatures. This methodology avoids reliance on outcomes of future GHG emission pathways, which vary and are likely to change. Regional impacts and rates of decline in chilling differ among the chill models, with the 0–7.2°C model indicating the greatest reduction and the Dynamic model the slowest rate of decline. Elevated and high latitude eastern Australian sites were the least affected while the three more maritime, less elevated Western Australian locations were shown to bear the greatest impact from future warming.

Managing Grapevines through Severe Heat: A Survey of Growers after the 2009 Summer Heatwave in South-eastern Australia

A survey of 92 vineyards, representing 10 winegrowing regions in south-eastern Australia, soon after exposure to a severe heatwave, revealed variation in the reported heat-related impact. This variation was observed between regions, within regions and within vineyards. Notably the estimates of losses were not always related to the amount of heat above a certain threshold but to the management practices employed in the lead-up and through the event. Applicable and achievable recommendations for managing severe heat events have resulted from this assessment. We believe this method of capturing information from the diverse knowledge-base of managers is a very effective way to reveal potential adaptive capacity to a changing climate.

Environmental Factors and Seasonality Affect the Concentration of Rotundone in Vitis vinifera L. cv. Shiraz Wine

Rotundone is a sesquiterpene that gives grapes and wine a desirable ‘peppery’ aroma. Previous research has reported that growing grapevines in a cool climate is an important factor that drives rotundone accumulation in grape berries and wine. This study used historical data sets to investigate which weather parameters are mostly influencing rotundone concentration in grape berries and wine. For this purpose, wines produced from 15 vintages from the same Shiraz vineyard (The Old Block, Mount Langi Ghiran, Victoria, Australia) were analysed for rotundone concentration and compared to comprehensive weather data and minimal temperature information. Degree hours were obtained by interpolating available temperature information from the vineyard site using a simple piecewise cubic hermite interpolating polynomial method (PCHIP). Results showed that the highest concentrations of rotundone were consistently found in wines from cool and wet seasons. The Principal Component Analysis (PCA) showed that the concentration of rotundone in wine was negatively correlated with daily solar exposure and grape bunch zone temperature, and positively correlated with vineyard water balance. Finally, models were constructed based on the Gompertz function to describe the dynamics of rotundone concentration in berries through the ripening process according to phenological and thermal times. This characterisation is an important step forward to potentially predict the final quality of the resultant wines based on the evolution of specific compounds in berries according to critical environmental and micrometeorological variables. The modelling techniques described in this paper were able to describe the behaviour of rotundone concentration based on seasonal weather conditions and grapevine phenological stages, and could be potentially used to predict the final rotundone concentration early in future growing seasons. This could enable the adoption of precision irrigation and canopy management strategies to effectively mitigate adverse impacts related to climate change and microclimatic variability, such as heat waves, within a vineyard on wine quality.

Challenges in predicting climate change impacts on pome fruit phenology

Climate projection data were applied to two commonly used pome fruit flowering models to investigate potential differences in predicted full bloom timing. The two methods, fixed thermal time and sequential chill-growth, produced different results for seven apple and pear varieties at two Australian locations. The fixed thermal time model predicted incremental advancement of full bloom, while results were mixed from the sequential chill-growth model. To further investigate how the sequential chill-growth model reacts under climate perturbed conditions, four simulations were created to represent a wider range of species physiological requirements. These were applied to five Australian locations covering varied climates. Lengthening of the chill period and contraction of the growth period was common to most results. The relative dominance of the chill or growth component tended to predict whether full bloom advanced, remained similar or was delayed with climate warming. The simplistic structure of the fixed thermal time model and the exclusion of winter chill conditions in this method indicate it is unlikely to be suitable for projection analyses. The sequential chill-growth model includes greater complexity; however, reservations in using this model for impact analyses remain. The results demonstrate that appropriate representation of physiological processes is essential to adequately predict changes to full bloom under climate perturbed conditions with greater model development needed.

Terpene evolution during the development of Vitis vinifera L. cv. Shiraz grapes

The flavour of wine is derived, in part, from the flavour compounds present in the grape, which change as the grapes accumulate sugar and ripen. Grape berry terpene concentrations may vary at different stages of berry development. This study aimed to investigate terpene evolution in grape berries from four weeks post-flowering to maturity. Grape bunches were sampled at fortnightly intervals over two vintages (2012-13 and 2013-14). In total, five monoterpenoids, 24 sesquiterpenes, and four norisoprenoids were detected in grape samples. The highest concentrations of total monoterpenoids, total sesquiterpenes, and total norisoprenoids in grapes were all observed at pre-veraison. Terpenes derived from the same biosynthetic pathway had a similar production pattern during berry development. Terpenes in grapes at harvest might not necessarily be synthesised at post-veraison, since the compounds or their precursors may already exist in grapes at pre-veraison, with the veraison to harvest period functioning to convert these precursors into final products.

Comparison data of common and abundant terpenes at different grape development stages in Shiraz wine grapes

Terpenoids were extracted from grape vine bunches during plant development and analysed by GC-MSD. The grapevines analysed were from a commercial harvest of Vitis vinifera cv. Shiraz. The terpenoids were analysed from 4 weeks post flowering (wpf) to harvest in one season. The data are presented with the structure of the compound and aroma profile and semi-quantified. The sub-class of sesquiterpenes was given special attention, and this data set describes the first analysis of these compounds during ripening of this important economic crop. Sesquiterpenes may have a hitherto described contribution to wine aroma. This data set may provide insight into biosynthetic pathways and aroma chemistry. Interpretation of our data and further discussion can be found in “Terpene evolution during the development of Vitis vinifera L. cv. Shiraz grapes” (Zhang et al., 2016) [1].

Distribution of Rotundone and Possible Translocation of Related Compounds Amongst Grapevine Tissues in Vitis vinifera L. cv. Shiraz

Rotundone is an attractive wine aroma compound, especially important for cool climate Shiraz. Its presence in wine is mainly from the grape skin, but can also be found in non-grape tissues, such as leaves and stems. Whether rotundone is produced independently within different grapevine tissues or transported amongst non-grape tissues and grape berries remains unclear. The current study investigated the distribution of this compound in different vine tissues during development and studied the most likely mode of rotundone translocation—via phloem—using stable isotope feeding. In addition, local production of rotundone induced by herbivore feeding was assessed. Results showed that rotundone was firstly detected in the petioles and peduncles/rachises within the development of Vitis vinifera L. cv. Shiraz. Different grapevine tissues had a similar pattern of rotundone production at different grape developmental stages. In the individual vine shoots, non-grape tissues contained higher concentrations and amounts of rotundone compared to berries, which showed that non-grape tissues were the larger pool of rotundone within the plant. This study confirmed the local production of rotundone in individual tissues and ruled out the possibility of phloem translocation of rotundone between different tissues. In addition, other terpenes, including one monoterpenoid (geraniol) and six sesquiterpenes (clovene, α-ylangene, β-copaene, α-muurolene, δ-cadinene, and cis/trans-calamenene) were, for the first time, detected in the ethylenediaminetetraacetic acid-facilitated petiole phloem exudates, with their originality unconfirmed. Unlike other herbivore-induced terpenes, herbivorous activity had limited influences on the concentration of rotundone in grapevine leaves.