GiESCO 2017 High temperature impact on bunch stem and grape berry physiology

FINAL REPORT to WINE AUSTRALIA

Project Number: AGT 1606 Principal Investigator: Julia Gouot

Research Organisation: National Wine and Grape Industry Centre Date: 13 December 2017 GiESCO 2017 - High temperature impact on bunch stem and grape berry physiology

Abstract

The 20th GiESCO meeting was dedicated to sustainable viticulture in a climate change scenario. It was held in Mendoza (Argentina) from 5-10 November 2017. A total of 60 oral papers and more than 130 posters were presented during the conference around diverse topics such as climate change, sustainability, breeding, vine physiology and vineyard management. Several strategies to adapt to climate change were presented during this conference and in particular, how to adapt to rising temperatures. Viticultural practices such as shading, irrigation and hydrocooling are already being used, but these may be difficult to afford or justify on a large scale as the consequences of climate change on the world’s warmer and hot climate regions become more pronounced. In the medium- term, adaptation of canopy and floor management practices may help to offset the effects of climate change on both vineyard water balance and temperature. However, changing the growing area and moving vineyards to higher altitudes or cooler latitudes, as well as identifying thermo-tolerant varieties and breeding new ones may be the type of approaches needed for long-term industry adaptation.

Executive summary

The travel bursary awarded by Wine Australia to Julia Gouot was used to fund travel to attend the 2017 GiESCO conference. The 20th GiESCO meeting was held in Mendoza (Argentina), 5-10 November 2017, and was dedicated to sustainable viticulture and winemaking in a climate change scenario. A total of 60 oral papers and more than 130 posters were presented during the conference around diverse topics such as climate change, sustainability, breeding, vine physiology and vineyard management. ‘Vineyard management and mechanisation’ was the largest session with 16 orals and 45 posters, followed by ‘climate change, sustainability and zoning’ and ‘vine physiology’, each with 13 orals, and 26 and 27 posters, respectively. The ‘breeding, varieties, clones and rootstocks’ session comprised 7 orals and 6 posters, while other sessions such as ‘plant protection’, ‘socioeconomics’ and ‘oenology’ only contained posters. The professional day focused on ‘precision viticulture, modelling and new technologies’ as well as ‘vineyard management and mechanisation’. The use of new technologies such as robots and phone applications, is greatly expanding and presentations focused on early yield predictions. Julia Gouot presented her preliminary PhD results in an oral presentation on the effect of extreme high temperature on bunch stem and berry physiology, on which she received valuable feedback. The conference allowed her to expand her knowledge and network in viticulture research by meeting and exchanging with viticulture researchers who have many years of experience in this field. She came back with new experimental ideas and learnt about low-cost tools which could be used for her experiments.

To report to the Australian grape and wine industry about the conference, an article summarising highlights of the GiESCO meeting will be submitted to the Wine and Viticulture Journal (see manuscripts in preparation attached).

Report

This report includes two appendices:

• Highlights of GiESCO 2017 (manuscript under preparation), which will be submitted for publication to the Wine and Viticulture Journal in the 2018 January/February edition on sustainability. • Full text manuscript of Julia’s paper presented at GiESCO 2017 (oral presentation).

Opportunities for collaboration

Julia discovered new tools that can be implement during her experiments. Possible collaborations were discussed with Dr Javier Tardaguila from the University of La Rioja (Spain), who with his team developed two phone applications to measure berry setting by taking pictures before and after flowering. These applications could be used, combined with the local bunch heaters built by Julia, to assess the effect of high temperature around flowering without the use of flower bags which impact on light exposure.

GiESCO international meeting: sustainable viticulture in climate change scenario

Summary of the meeting

The 20th Group of International Experts of vitivinicultural Systems for CoOperation (GiESCO) meeting was held in Mendoza (Argentina), 5-10 November 2017, and was dedicated to promoting the sustainability of viticulture and winemaking under future climate change scenarios. A total of 60 oral presentations were given at the conference, and together with more than 130 posters, the program covered diverse topics such as climate change, sustainability, breeding, vine physiology and vineyard management. ‘Vineyard management and mechanisation’ was the largest session with 16 oral presentations and 45 posters, followed by ‘climate change, sustainability and zoning’, and ‘vine physiology’, each with 13 oral presentations, and 26 and 27 posters, respectively. The professional day focused on precision viticulture, modelling and new technologies as well as vineyard management and mechanisation. The use of new technologies such as robots and phone applications is greatly expanding and presentations focused on early yield predictions.

At the conference, five out of the 60 oral presentations were given by Australian scientists and three out of the five presentations were given during the professional day, showing the strong industry relevance of Australian research:

Simple trait measurements across rootstock genotypes indicates performance as field grown, grafted vines (Peter Clingeleffer, CSIRO Agriculture and Food, Adelaide)

Early yield prediction through grapevine bud image analysis (Cassandra Collins, University of Adelaide)

Late pruning can delay maturity and preserve wine chemical and sensory attributes in Barossa Valley Shiraz (Martin Moran, South Australian Research and Development Institute, Adelaide)

The development of a low-input under-vine floor management system which improves profitability without compromising yield or quality (Chris Penfold, University of Adelaide)

Locally applied high air temperature significantly altered bunch stem and berry physiology (Julia Gouot, National Wine and Grape Industry Centre, Wagga Wagga).

Climate change adaptation methods

For the International Organisation of Vine and Wine (OIV), environmental protection and preservation are the most important concerns at the world scale. Preservation of natural resources, such as energy and water, as well as protection of the environment via reduction of phytosanitary product usage and management of by-products or waste are essential. But by far, the most important environmental threat for modern viticulture is climate change. Several strategies to adapt to climate change were presented during this conference and in particular, how to adapt to rising temperatures. Viticultural practices such as shading, irrigation and hydrocooling are already being used, but these may be difficult to afford or justify on a large scale as the consequences of climate change on the world’s warmer and hot climate regions become more pronounced. In the medium-term, adaptation of canopy and floor management practices may help offset the effects of climate change on both vineyard water balance and temperature. However, changing the growing area and moving vineyards to higher altitudes or cooler latitudes, as well as identifying thermo-tolerant varieties and breeding new ones may be the type of approaches needed for long-term industry adaptation.

Current projects around the world are investigating such strategies, and a number were presented at the conference. For example, Laure De Resseguier, Coralie Laveau and colleagues (Bordeaux Sciences Agro, Bordeaux, France) studied two wine regions in France: Irouleguy, vineyard at the foot of the Pyrenees mountain range, on the border between France and Spain, and Saint-Emilion, 20 km east of Bordeaux, the latter larger in area but lower in altitude. With the use of numerous temperature sensors, diverse temperature parameters were recorded at the meso scale. Differences in minimum temperature were measured between sites with an amplitude of up to 11 °C on a given day, and grape sugars and acids were correlated with altitude. In Israel, in the Negev desert, shade cloth was used to mitigate the effect of high solar radiation and temperature (Noam Reshef, University of the Negev, Sede Boqer, Israel). The experiment was performed at the bunch level to gain a mechanistic understanding of the combined effect of reduced light and temperature on berry metabolism, independently of the canopy. Lower light intensity led to a reduction of amino acids and flavonols but increased yield, acids (malic acid), precursors of tannins and anthocyanins. Microclimate directly affected grape berry metabolism and significantly changed grape chemical composition at harvest. Shading bunches in the vineyard could be successfully used to maintain colour and acidity while increasing yield in case of extreme heat events.

In Montpellier, France, Laurent Torregrosa and colleagues (Montpellier SupAgro, France) are now looking at long-term adaptation with breeding programs. However, phenotypic and genetic diversity for berry traits impacted by temperature is not yet well known. The aim of this study was thus to first characterise the phenotypic diversity of 33 selected grapevine varieties. By following the accumulation of organic acids and sugars during berry growth and ripening, a considerable phenotypic diversity for malic and tartaric acid content as well as for sugars and berry size was observed. These findings could be used to breed varieties capable of maintaining acidity under high temperature. Furthermore, increased average temperature is also shifting grapevine phenology all around the world. Studies in Australia (Martin Moran, South Australian Research and Development Institute, Adelaide), Chile (Carolina Salazar-Parra, Instituto de Investigacinoes Agropecuarias, Santiago, Chile) and Greece (Stephanos Koundouras, Aristotle University of Thessaloniki, Thessaloniki, Greece) presented similar results on slight increases in temperature throughout grapevine development and advancement of ripening and harvest. Short spells of extreme high air temperature are also critical for berry composition and survival. In a glasshouse experiment on potted Shiraz vines (Julia Gouot, National Wine and Grape Industry Centre, Wagga Wagga), a few hours (12 or 30 h) of extreme high day temperature (VHT) (maximum temperature reached was 53 °C) applied at the bunch level led to severe bunch stem and berry desiccation. However, low air (LT) and high air temperature (HT) (maximum temperature reached was 37 °C and 45 °C, respectively) had no effect on berry size (Figure 1).

A B

Figure 1. Julia Gouot presenting PhD research on the impact of high temperature on grapevine physiology (A) and experimental results of the effect of low, high and very high temperature on berry fresh weight (B).

Climate risks impacting on grape and wine quality are not only limited to high temperature. An interview conducted by Dr Mercedes Fourment (Facultad de Agronomia, Montevideo, Uruguay) in Southern Uruguay identified high temperature but also other climatic factors that could contribute to yield loss, shift in phenology and grape quality in this region. These risks were reported by grapegrowers and increases in extreme events, decrease in cold units in winter, increase in hours with temperatures above 35 °C, precipitation increase during the vegetative cycle and/or during the ripening period were all perceived as potential risks due to climate variability. Examples of damage and subsequent suggested adaptation strategies are summarised in Table 1.

Berry composition Berry composition Risk perceived Yield Phenology Pest and disease pressure (primary metabolites) (secondary metabolites)

Cycle delay due to canopy Problems in synthesis Direct loss due to grape Increase in incidence and damage leading to the and accumulation of damage and indirect loss due Loss of aroma and colour severity of diseases due to generation of other points compounds, which may to foliar area damage. berry splitting 1. Increase in of growth (laterals) lead to lower TSS. extremes events Avoid severe defoliation Adaptation of preventive Vinification management such as chaptalisation for reducing cropload or exposing Avoid severe defoliation disease management to inadequate ripeness bunches decrease sanitary pressure

Decrease in reproductive differentiation Budbreak heterogeneity Maturation heterogeneity N/A (number of flowers and subsequent number of berries) 2. Decrease in cold unit during winter Use of chemicals to Time of pruning. Use of Adaptation of preventive homogenise budbreak and Vinification management such as chaptalisation for chemicals to homogenise disease management to increase number of shoots per inadequate ripeness budbreak decrease sanitary pressure plant

Increase in TSS and Increase of polyphenol Advanced and/or shorter decrease of acidity. synthesis if blockage Reduction of berry size by phenological phases and Severe water stress does not occur. Loss of N/A 3. Increase in dehydration maturation might cause blockage of anthocyanins by hours of maturity degradation temperature o Adaptation of preventive above 35 C Green management Night harvest to avoid compound degradation and Avoid severe defoliation on disease management to (defoliation and shoot vinification management. Improvement of white grapes avoid spraying at extreme thinning) to decrease canopy transport to winery temperature Stimulation of vegetative Decrease due to reduction of growth and delay of Dilution of TSS. Increase in incidence and berry setting if rain occurs phenology. Spring rainfalls Imbalance of primary Loss of aroma and colour severity of diseases which during flowering impact on flowering and compounds affect leaves and grapes 4. Precipitation fruitset increase during the Adaptation of preventive vegetative cycle Change to rootstock which disease management to Bunch thinning to favour tolerate better root Favour adequate leaf area to improve ripening decrease sanitary pressure adequate ripening asphyxia or are less and decrease the number of vigorous spraying

Increase due to berry Promotion of vegetative Dilution of TSS. Increase in incidence and hydration and increased berry growth which can delay Imbalance of primary Loss of aroma and colour severity of diseases due to volume phenology and maturation compounds berry splitting 5. Precipitation Probability of negative increase during the consequence ripening period Change to rootstock which Low Adaptation of preventive Bunch thinning to favour tolerate better root Vinification management such as chaptalisation Medium disease management to adequate ripening asphyxia. Change to early when grapes are inadequately ripened High decrease sanitary pressure varieties

Probability of negative Adaptive capacity consequence Adaptive responses High Low Moderate

Low Tactical reactive

Medium Tactical anticipatory

High

Table 1. AdaptiveMatrix ofcapacity vulnerability and adaptation of vineyards of Southern Uruguay depending on Adaptive responses Highclimatic threatsLow perceived byModerate growers. Adapted with permission from Mercedes Fourment, Milka Tactical reactive Tactical anticipatory Ferrer, Gerard Barbeau and Herve Quenol – GiESCO 2017.

In Argentina, the main threat from climate change is an increase in average and extreme temperatures as well as a potential lack of water. Annual rainfall in Mendoza, one of the main wine regions of the country, is only 250 mm and water used for irrigation in this region and others comes from melted snow from the Andes mountains. Water is a precious and scarce resource in this hot region (MJT= 26 °C) and the work ahead will include significantly improving water management, as flood irrigation is the main system used to grow commercial grapes. For example, with climate change, rainfalls are expected to increase during winter in the Andes mountain range and one strategy will be to build reservoirs to store water. Also, the establishment of a meteorological station network would help to track precipitation variations and increase efficiency in water usage for irrigation according to crop requirements. Research at the Instituto Nacional de Tecnologia Agropecuaria (INTA) in Mendoza is also investigating the use of different trellis systems (e.g. Pergola, Ramé) to maintain berry quality while increasing yield and protecting berries from sunburn (Figure 2).

A B

C D

Figure 2. Santa Julia vineyard in the Mendoza wine region under flood irrigation (A), Clos de los Siete vineyard in the Valley de Uco with Andes mountain range in the background (B), Potrerillos artificial lake, main source of water for Mendoza (C) and vines grown under double Ramé trellis system in the INTA experimental vineyard (D).

In summary, many preventive mitigation methods for climate change are already available in the vineyard for short-term adaptation (shading, hydrocooling, kaolin berry sunscreen) but further research is needed for long-term adaptation. In addition, adaptive methods in the winery can also be used if the harvested grapes do not match expected quality. In particular, wine processing such as dealcoholisation and yeast strains that use more sugar to produce less ethanol, or non-Saccharomyces strains can be used to reduce the amount of ethanol in the final wine to match requirements.

The next GiESCO meeting will be in Thessaloniki, Greece in 2019 and scientists and students are looking forward to meeting again to discuss research and present innovations in the field of viticulture.

Acknowledgment

The authors would like to thank Wine Australia and the National Wine and Grape Industry Centre for funding Julia Gouot’s travel to the GiESCO conference in Mendoza. Julia Gouot’s PhD research is funded by a Charles Sturt University Postgraduate Research Scholarship. The authors also thank Mercedes Fourment (Facultad de Agronomia, Montevideo, Uruguay) for the matrices of vulnerability and adaptation of Southern Uruguay vineyards.

LOCALLY APPLIED HIGH AIR TEMPERATURE SIGNIFICANTLY ALTERED BUNCH STEM AND GRAPE BERRY PHYSIOLOGY

LA TEMPERATURE ELEVEE DE L’AIR, APPLIQUEE LOCALEMENT, MODIFIE SIGNIFICATIVEMENT LA PHYSIOLOGIE DES RAFLES ET DES BAIES DE RAISINS GOUOT, Julia 1, 2,*, SMITH, Jason 1, 3, HOLZAPFEL, Bruno 1, 4, and BARRIL, Celia 1, 2 1 National Wine and Grape Industry Centre, Charles Sturt University, Mambarra Drive, Wagga Wagga, NSW 2678, Australia 2 School of Agricultural and Wine Sciences, Charles Sturt University, Boorooma Street, Locked Bag 588, Wagga Wagga, NSW 2678, Australia 3 Hochschule Geisenheim University, 65366 Geisenheim, Germany 4 New South Wales Department of Primary Industries, Pugsley Place, NSW 2795, Australia

*Corresponding author: [email protected]

Abstract Climate change projections show major changes regarding temperature: a global warming with an increase average temperature and in frequency and severity of punctual heat events. Such changes in temperature will significantly affect the grapevine growing cycle and the bunch microclimate, known to be a major regulator of grape metabolism. A heating system adapted from Tarara et al. (2000) was built to heat individual bunches without changing their exposure. Two experiments were performed to screen the effect of several independent parameters related to temperature. The first experiment used a factorial design and compared average day temperature (25 versus 40 °C) and night temperature (20 versus 30 °C). The second one combined three intensity levels (30, 37 and 44 °C) and five durations (varying from 3 to 39 hours) of heat treatments using a Doehlert design. Experiments were conducted in a UV-transparent glasshouse, where temperature was recorded using thermocouples (air) and a thermal camera (bunch). Light, humidity, CO2 and vine physiology were either controlled or monitored. Experiment 1 showed that day temperature had a greater effect on berry weight compared to night temperature. However, both induced a change in maturation rate and berry composition. Experiment 2 showed that the effect of temperature on berry weight was proportional to the intensity of temperature. Also, average heat at 44 °C induced bunch stem necrosis and berry shrivelling symptoms, independently of the length of the treatment, suggesting that changes in physiology were irreversible for berries reaching such a high temperature even for a short amount of time. Key words: high temperature, bunch, berry composition, experimental design Résumé Les modèles de changement climatique prédisent des changements majeurs concernant la température : un réchauffement climatique avec une température moyenne accrue et une augmentation de la fréquence et de la gravité des vagues de chaleur. De tels changements de température affecteront de manière significative le cycle de croissance de la vigne et le microclimat de la grappe, connu pour être un régulateur majeur du métabolisme du raisin. Un système de chauffage adapté de Tarara et al. (2000) a été construit pour chauffer individuellement des grappes sans changer leur exposition. Deux expériences ont été effectuées pour examiner l'effet de plusieurs paramètres indépendants liés à la température. La première expérience utilise un plan d’expérience factoriel et compare la température diurne moyenne (25 contre 40 °C) et la température nocturne (20 contre 30 °C). La deuxième combine trois niveaux d'intensité (30, 37 et 44 °C) et cinq niveaux de durée (variant de 3 à 39 heures) de traitements thermiques à l'aide d'un plan de Doehlert. Les expériences ont été menées dans une serre transparente aux UV, où la température a été enregistrée à l'aide de thermocouples (air) et d'une caméra thermique (grappe). La lumière, l'humidité, le CO2 et la physiologie de la vigne, ont été soit contrôlés ou soit surveillés. L'expérience 1 montre que la température du jour a un effet plus important sur le poids des baies que la température de la nuit. Cependant, les deux ont induit une modification de la vitesse de maturation et de la composition des baies. L'expérience 2 a montré que l'effet de la température sur le poids des baies est proportionnel à l'intensité de la température. En outre, la vague de chaleur à 44 °C a induit des symptômes ressemblant à la nécrose de la rafle et au flétrissement des baies, indépendamment de la durée du traitement, ce qui suggère que les changements de physiologie sont irréversibles lorsque les baies atteignent une température aussi élevée même pendant un court laps de temps. Mots clés : haute température, grappe, composition des baies, plan d’expérience Introduction Average temperature increases of 2 to 4 °C, consistent with 50 year climate projections for Australia, have already been shown to modify grapevine physiology, and fruit and wine quality (Sadras and Soar, 2009). Also, short heat events of unusually high temperatures over a day or more, dramatically affect grapevine canopy and fruit yield (Webb et al, 2009), mainly due to sunburn and berry shrivelling. According to climate predictions, both average temperatures and extremes are expected to increase (O’Neill et al, 2017), and heat waves will be longer, more frequent and more intense. Shiraz is one of the most important varieties in Australia’s warm and hot climate production areas, and irrigated Shiraz vines have been found to adapt their canopy to short periods of high temperature with evapotranspiration (Soar et al, 2009). However, bunch temperature is not only dependant on air temperature and evapotranspiration but also on solar radiation, which can lead to significantly higher skin surface temperature in black berries (Tarara et al, 2000). It is therefore important to understand potential impacts of extreme high berry temperature created by heat events on fruit attributes and quality, independently of canopy temperature. The aim of this study is to examine how extreme high temperatures affect Shiraz grape bunch physiology. In particular, this study aimed to determine which parameters among day and night heating, phenological stage, duration and intensity are critical, using novel complex experimental designs. Materials and methods Plant materials and layout Experiments were conducted in a research glasshouse located at Charles Sturt University, Wagga Wagga (35° S, 147° E) and build with Plexiglas® (PLEXIGLAS® Alltop SDP 16/980 (/1053, /1200) – 64) transmitting 70% of UV (200-400 nm) and 90% of visible light. The glasshouse was cooled with an evaporative air-conditioning system, so that temperature was reduced relative to the outside temperature. Two experiments were carried out from October 2016 until March 2017. For Experiment 1, 6-year-old own-rooted Shiraz grapevines (V. vinifera L.) were used. Three weeks before flowering, vines were moved into the glasshouse. Four dormant 9-year-old, own-rooted Shiraz grapevines (V. vinifera L.) were used for Experiment 2. They were first stored in a dark cool room to delay bud-break while Experiment 1 was completed, and then moved straight into the glasshouse in November. After budburst for both experiments, the emerging shoots were selected and trained vertically along stakes. Prior to flowering, vines were thinned to six shoots and a uniform number of bunches: four bunches per vine for Experiment 1 and ten bunches per vine for Experiment 2. All bunches were trimmed to 30 berries at the onset of véraison for Experiment 2. In both experiments, leaf numbers were adjusted to 48 per vine and shoot tips were cut and new laterals were regularly removed. Vines were arranged on steel mesh benches in the glasshouse, following an experimental layout generated using DiGGeR (Coombes, 2009). Vines were individually watered using a drip system so as to fully saturate the soil each time. Vines were regularly sprayed with wettable sulfur, and fertilised with Megamix (Megamix Plus®, RUTEC, Tamworth) and additional magnesium sulphate. Treatment application Treatments were applied to individual bunches using a design based on Tarara et al, (2000). Air blowers, consisting of PVC tubes connected to 100 mm diameter flexible ducting were placed 10 cm far from each bunch with a 45-degree angle. Hot and ambient air was blown onto the bunch (0.4 m3/min) with axial fans installed at the lower end of the delivery tube. Typical exit velocity was 1 ± 0.2 m/sec measured with a portable anemometer for each individual blower. Hot air was produced with commercial heaters (2000 W) blowing air at 65 °C at 10 m3/min into an insulated box (1 m3) and delivered through flexible ducts to the fans. Experimental designs For experiment 1, a complete factorial design (Table 1) was applied to assess the effect of two independent variables, day temperature and night temperature, on berry and bunch stem physiology. Each vine was treated as a replicate (n=3). Three temperature-controlled treatments were applied during the experimental phase: day heating (DH), night heating (NH) and day and night heating (DNH) and compared to a control (C), for which ambient air was delivered at the same rate. Tested temperatures varied between two levels: high and low, and the system was set up to maintain a temperature difference (dT) of +8 °C during the day and +6 °C at night. Treatments were applied just after berry set (E-L 27- 28), and continued for a period of four days and three nights. The day treatment ran between 7:00 and 19:00 hrs and the night treatment from 20:00 to 06:00 hrs. For experiment 2, a non-factorial Doehlert design (Doehlert, 1970) (Table 2) was applied to study the effect of two independent variables: average day temperature and duration of treatment. Three temperature treatments were tested: low (30 °C, LT), high (37 °C, HT), and very high (44 °C, VHT). The night temperature was not modified. Five treatment durations, varying between 3 and 39 hours, were applied over a period of three days between 07:00 and 20:00 hrs. Each of these treatment periods were centred on 13:30 hrs of the second day. Treatments were applied just after véraison (E–L 35-36). Untreated vines (Experiment 1) or bunches (Experiment 2) were used as reference without any blowing or heating (Ref).

Temperature measurements

Temperature of the air blown on each bunch (Tair) was measured by fine-wire thermocouples (T-type) positioned between the exit of the PVC tube and the middle of the bunch. Sensor signals were recorded every 10 sec by two data acquisition system (AM-25T and CR-1000, Campbell Scientific, Logan, UT, USA) during treatment application. Berry surface temperature (Tberry) was also measured using an infrared thermal camera (FLIR ONE, FLIR Systems, OR, USA). Data were extracted using the FLIR software and the image processing toolbox (Matlab). Sample collection and heat damage assessment Berries were sampled from the bottom, middle and top of the bunch from treatment application through to harvest. Experiment 1 was harvested at véraison on December 27 and Experiment 2 at maturity (23 °Brix) on March 17. Each bunch was assessed for heat damage at harvest. Percentage of heat damages were visually rated according to the damage score card from Webb et al. (2009). Statistical analysis The effect of day temperature, night temperature, and their interaction on harvest berries was determined by two-way ANalysis Of VAriance (ANOVA). Scatterplot matrices were used to assess correlations between duration, intensity (average and maximum temperature reached) and berry weight. Observed correlations were tested for linear regression. Data analysis was performed using R software (version 3.2.5). Results and discussion Temperature Despite an effective cooling system, the glasshouse temperature was dependent on outside temperature and solar radiation. The system successfully maintained a constant dT between control and heated treatments during both experiments, although it was less effective on sunny days. For Experiment 1, the day time dT was 8 ± 2 °C but was maintained around 5.7 ± 0.4 °C at night (Fig. 1A). The maximum Tair varied between 37.2 and 44.8 °C during the day and 28.9 and 32.8 °C at night. These temperatures were realistic compared to the maxima recorded around berry set, during the 2009 November heat wave in Australia. For Experiment 2, the maximum Tair of the air supplied to heated fruit (HT) varied between 39.4 and 45.9 °C during the day which is similar to heat wave temperature recorded around véraison (Fig. 1B). However, VHT reached 53 °C, a temperature never recorded in an Australian wine grape growing region. A recent study in the Negev desert in Israel (Reshef et al, 2017) recorded a maximum of 50 °C at the surface of exposed grape berries and such high temperature may be reached in the future. Average, delta and maximum temperatures were correlated (p=0.85) (Fig. 2), regardless of the period and length of treatment. Tberry showed differences in temperature between the bottom, middle and top part of the exposed face of the bunch (Fig. 3). The temperature of the top of the bunch was higher than that of the middle due to direct sun exposure. The bottom of the bunch was also higher than the middle due to the 45 ° angle of the air delivery tube. Small differences were also recorded between Tair and Tberry (data not shown). Berry growth and heat damage Results from Experiment 1 showed that day temperature had a greater effect on berry physiology compared to night temperature. Day temperature significantly affected berry growth (p<0.001) while night temperature did not (p=0.099) and no interactions were found between both parameters (p=0.22). Fresh mass of healthy berries was dramatically reduced by 28 and 30% by day temperature for DH and DNH treatments, respectively. NH and C berry mass was not significantly impacted. In addition, some of the young green berries, mostly at the bottom of the bunch but also in random positions, quickly started to turn brown leading to desiccated berries at harvest. In Experiment 2, the length of the treatment had no direct effect on berry weight. The established regressions (Fig. 2) showed that only temperature had a critical effect on berry weight but no linear relations were found. HT (37 °C) had no effect on berry weight compared to LT and Ref and average fresh weights were not significantly different whereas VHT (44 °C) significantly reduced berry weight. Berry weight was the same, 1 ± 0.2 g/berry (average between Ref, LT and HT), at maximum temperatures varying from 35 to 50 °C, but dropped to 0.23 ± 0.06 g/berry (VHT/30 h) and 0.3 ± 0.2 g/berry (VHT/12 h). Such large loss in berry weight was due to berry shrivelling and a critical temperature threshold was highlighted around 50 and 53 °C. Among the different reasons that could contribute to berry weight loss (Krasnow et al, 2010), bunch stem necrosis symptom was one identified in both experiments. The development of desiccated berries and necrotic tissue started two hours after the start of the day heated treatment in both experiments. Berry browning and possible interruption of water transport into the berry both led to a total of 8% of shrivelled berries for DH and 24% for DNH. No necrosis was observed for Ref, C and NH. For Experiment 2, 0, 10 and 90% fruit damage were recorded at LT, HT and VHT, respectively. Necrosis and berry shrivelling started at the tip of the bunch for most bunches, due to higher bottom temperature, but wings were also sometimes affected, probably due to higher temperature depending on sun exposure.

Conclusion In this study, short but extreme temperature treatments had a critical effect on bunch physiology inducing bunch stem necrosis and berry shrivelling. These symptoms started to appear at extreme high temperature only, and highlighted a critical maximum temperature threshold of 50 °C for irrigated Shiraz at véraison. Such symptoms also appeared at “lower” temperatures (around 43 °C) at berry set, suggesting that green berries are more sensitive to high temperature. High temperature, even for a short period of time, significantly altered grape bunch physiology irreversibly and led to severe berry desiccation. Acknowledgement The authors thank David Foster, Robert Lamont, Khoi Nguyen, Winfried Holzapfel and Lorenzo Pazzi for their help on this project and Wine Australia for funding conference attendance. Literature cited COOMBES, N.E., 2009. DiGGer, a spatial design program. Biometric bulletin, NSW Department of Primary Industries. DOEHLERT, D.H. 1970. Uniform shell designs. Applied statistics, 231-239. KRASNOW, M., MATTHEWS M., SMITH R., BENZ J., WEBER E. and SHACKEL K., 2010. Distinctive symptoms differentiate four common types of berry shrivel disorder in grape. California Agriculture, 64:155-159. O'NEILL, B.C., OPPENHEIMER M., WARREN R., HALLEGATTE S., KOPP R.E., PORTNER H.O., SCHOLES R., BIRKMANN J, FODEN W. and LICKER R., 2017. IPCC reasons for concern regarding climate change risks. Nat. Clim. Change, 7:28-37 RESHEF, N., WALBAUM N., AGAM N. and FAIT A., 2017. Sunlight Modulates Fruit Metabolic Profile and Shapes the Spatial Pattern of Compound Accumulation within the Grape Cluster. Front. Plant Sci. 8:70. SADRAS V.O. and SOAR C.J. 2009, Shiraz vines maintain yield in response to a 2–4 °C increase in maximum temperature using an open-top heating system at key phenostages. Eur. J. Agron., 31:250-258. SOAR, C.J., COLLINS M.J. and SADRAS V.O., 2009. Irrigated Shiraz vines (Vitis vinifera) upregulate gas exchange and maintain berry growth in response to short spells of high maximum temperature in the field. Funct. Plant Biology, 36:801-814. TARARA, J.M., FERGUSON J.C. and SPAYD S.E, 2000 A Chamber-Free Method of Heating and Cooling Grape Clusters in the Vineyard. Am. J. Enol. Vitic, 51:182-188. WEBB, L., WATT A., HILL T., WHITING J., WIGG F., DUNN G., NEEDS S. and BARLOW E., 2009. Extreme heat: managing grapevine response. GWRDC and University of Melbourne: Melbourne.

Table 2. Doehlert design for experiment 2 Coded variables Real variables Table 1. Factorial design for experiment 1 Duratio Duration Avg T° ( Name Avg T° Day Night Name n (h) °C) -1 -1 Control (fan day and night only) 0 0 21 37 HT/21 h +1 -1 Day heated + fan night +1 0 39 37 HT/39 h -1 +1 Night heated + fan day +0.5 +0.866 30 44 VHT/30 h +1 +1 Day and Night heated -0.5 +0.866 12 44 VHT/12 h / / Reference -1 0 3 37 HT/3 h -0.5 -0.866 12 30 LT/12 h

+0.5 -0.866 30 30 LT/30 h / / 31 Reference

A

B

Figure 1. Temperature record during experiment 1 (A) and experiment 2 (B) Figure 1. Températures enregistrées pendant les expériences 1 (A) et 2 (B)

Figure 2. Scatterplot matrices between (X1) berry weight (g/berry), (X2) duration (h), (X3) average and (X4) maximum temperatures (°C) for Experiment 2 Figure 2. Matrice de diagramme de dispersion entre (X1) le poids d’une baie (g/baie), (X2) la durée (h), les températures (X3) moyennes et (X4) maximums (°C) pour l’expérience 2

Figure 3. Infrared images of Tberry under control (top) and day heated condition (bottom). Tair recorded in the middle of the bunch at the time of the pictures are 35 and 42.1 °C for control and heated, respectively Figure 3. Images infrarouge de Tbaie pour la grappe control (haut) et chauffée pendant le jour (bas). Tair enregistrées au milieu de la grappe au moment de la photo sont 35 °C pour le control et 42.1 °C pour la chauffée