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The responses of two red grape varieties, Bovale Grande (syn. Carignan) and Cannonau (syn. Grenache), to temperature and natural UV radiation were studied in a three-years field experiment conducted in Sardinia (Italy), under Mediterranean climate conditions. Vines were covered with plastic films with different transmittances to UV radiation and compared to uncovered controls. Light intensity and spectral composition at the fruit zone were monitored and berry skin temperature was recorded from veraison. Total skin anthocyanin content (TSA) and composition indicated positive but inconsistent effects of natural UV light. Elevated temperatures induced alterations to a greater extent, decreasing TSA and increasing the degree of derivatives acylation. In Cannonau total soluble solids increases were not followed by increasing TSA as in Bovale Grande, due to both lower phenolic potential and higher sensitivity to permanence of high temperatures. Multi linear regression analysis tested the effects of different ranges of temperature as source of variation on anthocyanin accumulation patterns. To estimate the thermal time for anthocyanin accumulation, the use of normal heat hours model had benefit from the addition of predictor variables that take into account the permanence of high (>35 °C) and low (<15 °C and <17 °C) temperatures during ripening.

Background and Aims Under natural conditions the grapevine has shown different growth and physiological responses to high UV radiation. We evaluate the effect of natural and reduced UV‐B, UV‐A and photosynthetically active radiation (PAR) on vine growth, physiological status and berry composition in Bovale Grande (syn. Carignan) and Cannonau (syn. Grenache) field‐grown grapes. Methods and Results During the two seasons of the trial, UV‐screening treatments Visible + UV‐A and Visible, imposed with plastic tunnels from pea size onward, promoted a significant difference in UV and PAR transmission as compared with that of plants exposed to natural sunlight, but did not reduce canopy growth and yield. Plants adjusted leaf gas exchange and water status to both high and reduced UV and PAR radiation. The concentration of phenolic substances of berries was significantly higher under natural UV, whereas accumulation of anthocyanins responded differently in the two cultivars according to the duration of high temperature. Conclusions The results indicate that red grapes of Mediterranean origin are able to adapt growth and physiological responses to high natural UV and temperature, but accumulation of berry anthocyanins and phenolic substances can vary considerably according to sensitivity of cultivars to these abiotic factors. Significance of the Study Increasing knowledge on the acclimation responses to high UV and solar irradiance environments by grape cultivars may help to improve management practices towards greater adaption to global warming conditions and projected climate change.

The photosynthetic and photochemical adaptation of grapevine leaves to high UV radiation, under hot and dry summer conditions, was investigated in near-isohydric Cannonau (syn. Grenache) and nearanisohydric Bovale grande (syn. Carignan). From pea-size stage until harvest, vines with mild to moderate water deficit were subjected to UV-blocking treatment (-UV) and compared to a control exposed to sunlight (C). Canopy light and thermal microclimate, growth and density, maximum leaf gas exchange, primary photochemistry (PSII) and phenols were monitored. Average increments in canopy temperature under -UV tunnels during day-time and night-time were 3.3°C and 0.8°C in Bovale grande and 2.6°C and 1.1°C in Cannonau. Cultivars reached similar leaf area, intrinsic water-use efficiency and stem water potential under C and -UV. Cannonau showed lower stomatal conductance, maximum net assimilation and transpiration rates, but also faster recovery of PSII under heat and moderate water stress. UV radiation induced a stronger and longer impact on leaf assimilation, but the duration of elevated temperatures under −UV induced higher photoinhibition and lower photochemical efficiency. A similar degree of correlation between leaf temperature and gas exchange was found among cultivars and treatments. In Cannonau, leaf anthocyanin decreased due to heat-induced long-lasting PSII photoinactivation under C. Conversely, Bovale grande showed higher phenolic content stability, thus higher photoprotection and recovery of PSII functional units. Agronomical practices affecting leaf phenolic accumulation influence canopy acclimation to heat and high sunlight. Vineyard management must avoid excessive canopy sun exposure and duration of elevated temperatures to favour high assimilation, while reducing photoinactivation and heat damage.

Background and Aims Plant responses to solar radiation are difficult to quantify due to interannual weather variation and to interference by other environmental factors. This study assesses the extent of the effect of UV sunlight on the accumulation and partitioning of anthocyanins in the berry skin of two red grape cultivars. Methods and Results Ultraviolet screening treatments, visible + UV‐A and visible, applied to Bovale Grande (syn. Carignan) and Cannonau (syn. Grenache) field‐grown vines, in Sardinia, Italy, promoted a significant difference in the concentration of skin anthocyanins compared with that of plants exposed to natural sunlight. Thermal units for anthocyanin accumulation, estimated with an adjusted normal heat hours model, showed a highly significant difference between cultivars. The elevated duration of high temperature (HT>35°C) in the first season reduced the concentration of skin anthocyanins, with Cannonau showing greater sensitivity. Together with the light regimes, HT>35°C induced an alteration in the composition of the anthocyanins; both natural UV‐B and low flux of UV‐A promoted higher acylation. Conclusions Besides light intensity, spectral composition also influenced accumulation and partitioning of anthocyanins in berry skin. The extent of alteration differs among cultivars as the combined effect of natural UV and HT>35°C drives shifts in anthocyanins biosynthesis differently. Significance of the Study Extending knowledge of the role played by sunlight and temperature on accumulation of berry anthocyanins may help to define management practices that foster stability of berry must colour and favour an optimal phenolic profile.

The effect of deficit irrigation strategies on physiological performance, growth, source:sink balance, water productivity and berry composition of field-grown grapevines of Vitis vinifera L. cv. Cannonau (syn. Grenache)/1103P were investigated in Sardinia, Italy, in 2009. In two of the treatments, both sides of the root system received 50% and 25% crop evapotranspiration (ETc), referred to as strategies DI50 and DI25, respectively. In the third treatment, which included partial root-zone drying (strategy PRD), ETc was set at 50%. All three treatments were compared to a full irrigation control (strategy FI), thus 100% ETc. No severe water stress was imposed from berry development onwards. Strategies DI25 and PRD induced higher stomatal closure and leaf water-use efficiency. A slightly higher net assimilation rate was recorded in FI before véraison. During ripening, leaf area decreased in DI50 and DI25, but lateral shoots continued to grow in FI and PRD. Yield and pruning weight were higher in FI, but in all the treatments the vines were source:sink balanced and supported ripening. Irrigation water productivity was higher in DI25, and no significant differences in yield or water productivity were observed between PRD and DI50 irrigated with a similar volume of water. Full irrigation produced berries with a significantly higher fresh and dry weight, lower °Brix and higher malic acid at harvest, while PRD berries weighed less and had less titratable acidity, lower phenol content and a higher pH. Total anthocyanin contents were consistently lower in DI25 and PRD, with highest values measured in DI50. The treatments showed different anthocyanin profiles, with a higher concentration of acylated anthocyanin in DI25 and PRD.

Maximizing water use efficiency, yield, and plant survival under drought is a relevant research issue for almond-tree-growing areas worldwide. The intraspecific diversity of this species may constitute a valuable resource to address the resilience and productivity challenges that climate change poses to crop sustainability. A comparative evaluation of physiological and productive performance of four almond varieties: ‘Arrubia’, ‘Cossu’, ‘Texas’, and ‘Tuono’, field-grown in Sardinia, Italy, was performed. A great variability in the plasticity to cope with soil water scarcity and a diverse capacity to adapt to drought and heat stresses during fruit development were highlighted. The two Sardinian varieties, Arrubia and Cossu, showed differences in water stress tolerance, photosynthetic and photochemical activity, and crop yield. ‘Arrubia’ and ‘Texas’ showed greater physiological acclimation to water stress while maintaining higher yields, as compared to the self-fertile ‘Tuono’. The important role of crop load and specific anatomical traits affecting leaf hydraulic conductance and leaf gas exchanges efficiency (i.e., dominant shoot type, leaf size and roughness) was evidenced. The study highlights the importance of characterizing the relationships among almond cultivar traits that affect plant performance under drought in order to better assist planting choices and orchard irrigation management for given environmental contexts.

The contribution of light and thermal conditions to berry anthocyanin accumulation was investigated in grapevine Vitis vinifera L. cv. Cannonau/1103P subjected to different irrigation strategies in Sardinia, Italy in 2009. In two of the deficit irrigation treatments the root system received 50% and 25% crop evapotranspiration (ETc), referred to as DI50 and DI25, respectively. In the third treatment, which included partial root-zone drying (PRD), ETc was set at 50%. All three treatments were compared to a full irrigation control (FI), thus 100% ETc. Analysis of the thermal conditions during the growing season in 2009 provided evidence for a high frequency of elevated temperatures (> 30°C) during berry development. During ripening, the DI25 clusters intercepted significantly higher intensities (P < 0.01) of solar radiation, UV and PAR, particularly on the southeast canopy side, in comparison to FI and PRD. The analysis of berry temperatures in the DI treatments showed higher exposure to more than 35°C in the DI25 southeast berries. Thermal time for anthocyanin accumulation was computed for the DI50 and DI25 berries using normal heat hours (NHH). The patterns of daily NHH showed a reduction in thermal efficiency for anthocyanin accumulation during mid-ripening in the DI25 southeast berries compared to the DI50 ones. The higher temperatures at mid-ripening led to lower total anthocyanin contents in the DI25 berries. However, the coumaroyl-glucoside anthocyanin forms continued to increase in both the DI50 and DI25 berries, while a significant reduction in berry total contents of these forms was observed in FI and PRD. Both deficit irrigation and light conditions in the DI25 berries favoured the accumulation of more colourstable anthocyanins in the berry skin until harvest, namely p-coumaroyl-glucoside and acetyl-glucoside forms.