Assessing the growth response of Vitis vinifera L. cv. Xynisteri, Maratheftiko, Shiraz and Sauvignon Blanc to different irrigation regimes.

The world’s changing climate is placing great pressure on the resources for sustainable viticulture. With this, it has become necessary to investigate grape varieties that are well adapted to hot climates. The aims of this study were to (1) assess the response of Xynisteri to different irrigation regimes, and (2) compare the performance of Xynisteri, Maratheftiko, Shiraz and Sauvignon Blanc grown in pots with different irrigation regimes. Trial one was established in a commercial Xynisteri vineyard in Cyprus under three different irrigation regimes - full, 50% and no irrigation in 2019. Trial two compared three irrigation regimes - full, 50% and 25% in a potted trial of Xynisteri and Sauvignon Blanc conducted in Cyprus in 2019. Trial three was a potted trial of Xynisteri, Sauvignon Blanc, Maratheftiko and Shiraz with the same three irrigation regimes conducted in Australia in 2020/21. Vine performance and physiology measurements were taken in both trials. Fruit composition analysis, yield (field trial only), shoot, trunk and root mass measurements were performed at the end of the season. Few differences between measures were found between irrigation regimes in the field trial. Fruit composition analysis revealed fructose to be lowest in the full irrigation group compared to deficit and no irrigation treatments. The potted trial in 2019 demonstrated that for all three irrigation regimes, Xynisteri had higher stem water potential, stomatal conductance and chlorophyll content than Sauvignon Blanc. Xynisteri produced greater end of season root, shoot and leaf mass than Sauvignon Blanc under all irrigation regimes. In 2020/21, Xynisteri had greater end of season root, shoot and leaf mass than Maratheftiko and Sauvignon Blanc with Shiraz the lowest. Few significant differences in stem water potential were observed in the early stages of the trial. However, toward the end of the trial and with reduced irrigation, Xynisteri and Maratheftiko had higher stem water potential than Shiraz and Sauvignon Blanc. Xynisteri had higher stomatal conductance and chlorophyll content than Maratheftiko and both were higher than Sauvignon Blanc and Shiraz. These results indicate that Xynisteri in particular may possess better cultivar specific growth traits than Shiraz and Sauvignon Blanc when grown under the same environmental conditions and in turn may be a more appropriate choice in areas where water is limited.

Reduced Irrigation during Orchard Establishment Conserves Water and Maintains Yield for Three Cider Apple Cultivars

Irrigation water productivity is a priority for sustainable orchard management as water resources become more limiting. This study evaluated reduced irrigation (RI) as a management strategy for cider apple (Malus domestica Borkh.) production in 2019 and 2020 in northwestern Washington, which has a Mediterranean climate and averages 14.1 cm of precipitation from June to September. RI was evaluated on three cider apple cultivars, Dabinett, Porter’s Perfection, and Golden Russet, in their third and fourth leaf. Stem water potential (stem ψ) was measured weekly throughout the growing season to monitor water stress and implement the RI treatment: irrigation would be applied when stem ψ values dropped below −1.5 MPa, a threshold indicative of moderate water stress in apples. Soil water potential was monitored throughout the season, vegetative growth was assessed by measuring shoot length and non-destructive imaging of the plant canopy using lateral photography, and yield, fruit quality, and juice quality were measured at harvest. Moderate water stress as indicated by stem ψ did not occur either year, thus irrigation was never applied to the RI treatment plots. There was a negative relationship between average stem ψ and both yield and air temperature (P < 0.0001 for each); as yield increased by 5.9 kg per tree or temperature increased by 3.3 °C, stem ψ decreased by 0.1 MPa. The juice quality attributes of the three cultivars in this study were similar to their historic measures at this site and there were no differences due to irrigation treatment, likely because trees did not reach the threshold to induce physiological stress. Both years, trees in the RI treatment did not differ from the control treatment in vegetative growth, fruit yield, juice yield, or any juice quality attribute, but weight per fruit decreased by 7 g, and fruit firmness (measured only in 2020) increased by 2 N. Results from this study indicate that fruit yield and quality in an establishing orchard can be maintained when irrigation is reduced relative to crop water requirements that are estimated from a calculated water balance or relative to conventional grower practices for this region. This finding highlights the benefits of using plant water status to schedule irrigation.

Effects of natural clinoptilolite on physiology, water stress, sugar, and anthocyanin content in Sanforte (Vitis vinifera L.) young vineyard

In the Mediterranea area, major effects of climate change are a modification in rainfall patterns, an increase in temperature with an intensify in tropical nights, and an increase in incoming radiations, especially UV-Bs. Despite the various adaptation strategies, grapevines are sensitive to altered climatic conditions. This paper aims to assess the benefits of applying a new sustainable product to the soil that can implement farmers’ resources to adapt to this changing situation. Zeowine was realized by combining the properties of zeolite, which has excellent potential in many sectors such as in agriculture, with the organic substance of a compost obtained on a company scale from the reuse of waste processing grapes, pomace and stalks. The effects of two different soil management (Z – Zeowine, 30 t/ha dose and C – Compost, 20 t/ha dose) on vine physiology and berry compositions in Sanforte grapevines (new plantation) were studied during the 2019–2020–2021 growing seasons in the San Miniato area, Italy. The following physiological parameters of grapevines were measured: leaf gas exchange, leaf temperature, stem water potential and chlorophyll fluorescence. The results showed that Z increased single leaf photosynthesis, reduced leaf temperature and water stress. In addition, phenolic and technological parameters were studied. The Z-treated vines had higher sugar content and total and extractable anthocyanin content as well as berry weight. These results suggested that the application of zeolites added to compost in the vineyard to the soil can be a valid tool to mitigate the effects of climate change.

Microtensiometers Accurately Measure Stem Water Potential in Woody Perennials

Stem water potential (Ψstem) is considered to be the standard measure of plant water status. However, it is measured with the pressure chamber (PC), an equipment that can neither provide continuous information nor be automated, limiting its use. Recent developments of microtensiometers (MT; FloraPulse sensors), which can continuously measure water tension in woody tissue of the trunk of the tree, can potentially highlight the dynamic nature of plant water relations. Thus, this study aimed to validate and assess the usefulness of the MT by comparing the Ψstem provided by MT with those same measurements from the PC. Here, two irrigation treatments (a control and a deficit treatment) were applied in a pear (Pyrus communis L.) orchard in Washington State (USA) to capture the full range of water potentials in this environment. Discrete measurements of leaf gas exchange, canopy temperature and Ψstem measured with PC and MT were made every two hours for four days from dawn to sunset. There were strong linear relationships between the Ψstem-MT and Ψstem-PC (R2 > 0.8) and with vapor pressure deficit (R2 > 0.7). However, Ψstem-MT was more variable and lower than Ψstem-PC when Ψstem-MT was below −1.5 MPa, especially during the evening. Minimum Ψstem-MT occurred later in the afternoon compared to Ψstem-PC. Ψstem showed similar sensitivity and coefficients of variation for both PC and MT acquired data. Overall, the promising results achieved indicated the potential for MT to be used to continuously assess tree water status.

Establishing a Reference Baseline for Midday Stem Water Potential in Olive and Its Use for Plant-Based Irrigation Management

Midday stem water potential (SWP) is rapidly becoming adopted as a standard tool for plant-based irrigation management in many woody perennial crops. A reference or “baseline” SWP has been used in some crops (almond, prune, grape, and walnut) to account for the climatic influence of air vapor pressure deficit (VPD) on SWP under non-limiting soil moisture conditions. The baseline can be determined empirically for field trees maintained under such non-limiting conditions, but such conditions are difficult to achieve for an entire season. We present the results of an alternative survey-based approach, using a large set of SWP and VPD data collected over multiple years, from irrigation experiments in olive orchards located in multiple countries [Spain, United States (California), Italy, and Argentina]. The relation of SWP to midday VPD across the entire data set was consistent with an upper limit SWP which declined with VPD, with the upper limit being similar to that found in Prunus. A best fit linear regression estimate for this upper limit (baseline) was found by selecting the maximum R2 and minimum probability for various upper fractions of the SWP/VPD relation. In addition to being surprisingly similar to the Prunus baseline, the olive baseline was also similar (within 0.1 MPa) to a recently published mechanistic olive soil-plant-atmosphere-continuum (SPAC) model for “super high density” orchard systems. Despite similarities in the baseline, the overall physiological range of SWP exhibited by olive extends to about −8 MPa, compared to about −4 MPa for economically producing almond. This may indicate that, despite species differences in physiological responses to low water availability (drought), there may be convergent adaptations/acclimations across species to high levels of water availability. Similar to its use in other crops, the olive baseline will enable more accurate and reproducible plant-based irrigation management for both full and deficit irrigation practices, and we present tentative SWP guidelines for this purpose.

Monitoring vineyard water status using Sentinel-2 images: qualitative survey on five wine estates in the south of France

The wine industry must face many challenges because of climate change. One of them is the increase in temperatures and droughts events. These changes sometimes lead to yield losses and can also impact the quality of the wine produced (e.g., increased alcohol content). The management of available water is also a sensitive issue as water requirements for vineyard irrigation are quickly increasing in the south of France. In this context, there is a need for a decision tool that can help evaluate the vine water status through the entire growth season at a large scale. To address this issue, we have previously developed a model (see Laroche-Pinel et al. 2021a) which predicts the vine Stem Water Potential (Ψstem) using Sentinel-2 (S2) images. This model was developed based on a field campaign over three years. The present study now aims to investigate the feedback of winegrowers on the outputs of our model. Therefore, it was applied on the plots of five wine estates that do not belong to the set used in the initial paper. The qualitative results show interesting spatial and temporal consistency in accordance with winegrower knowledge, irrigation data, and weather forecast. The predicted Ψstemhighlights spatial variability in vine fields where a water source emerges and reflects the differences between vine fields with a drip or sparkling irrigation or without an irrigation system. The predicted Ψstem also clearly reacts to a peak in temperature. According to their feedback, three of the five winegrowers would be glad to use this service in the years to come.

Evaluating the Spectral and Physiological Responses of Grapevines (Vitis vinifera L.) to Heat and Water Stresses under Different Vineyard Cooling and Irrigation Strategies

Heat stress (HS) and water stress (WS) pose severe threats to viticulture, and effective management solutions to counter their effects on grapevine performance must be examined. In this study, we evaluated the physiological and spectral responses of Vitis vinifera L. cv. Sauvignon blanc to individual (HS) and combined (HS + WS) stress under four different cooling and irrigation strategies. The treatments were: standard drip irrigation (SI), extra drip irrigation (SI+), extra sprinklers irrigation (SPRI), and sustained deficit irrigation (SDI; 50% of SI). Compared to the other treatments, in the early stages after the occurrence of HS, the vine water status of SPRI and SI+ improved, with high stomatal conductance (gs) (SPRI) and stem water potential (Ψstem; SPRI and SI+). All the physiological indicators measured were significantly lower after the end of HS in the SDI treatment. We also identified the spectral response of grapevine to HS and combined HS and WS (resulting from SDI). Consistent with the physiological analysis, the proximal spectral responses of leaves identified SPRI and SI+ as putative cooling strategies to minimize vine HS. The vines undergoing combined stress (SDI) showed greenness amelioration 10 days after stress, as revealed by the greenness vegetation indices (VIs), i.e., Green Index (GI), Normalized Difference Greenness Vegetation Index (NDGI), and Visible Atmospherically Resistant Index (VARI). However, their physiological recovery was not achieved within this time, as shown by the Simple Ratio Index (SRI), Transformed Chlorophyll Absorption Ratio Index (TCARI), and TCARI/Optimized Soil-Adjusted Vegetation Index (TCARI/OSAVI). A three-step band selection process allowed the identification of the spectral traits’ responsive to HS and combined stress, i.e., 1336–1340 nm, 1967–1971 nm, and 600–604 nm.

Drought-Adaptive Mechanisms of Young Sweet Cherry Trees in Response to Withholding and Resuming Irrigation Cycles

The present work evaluates the main adaptive mechanisms developed by young sweet cherry trees (Prunus avium L.) to cope with drought. For this purpose, the young trees were subjected to two drought cycles with different water stress intensities followed by a recovery period. Three irrigation treatments were applied: control treatment (CTL) irrigated to ensure non-limiting soil water conditions; moderate water stress (MS) subjected to two drying cycles whose duration was dependent on the time elapsed until the trees reached values of midday stem water potential (Ψstem) of −1.3 and −1.7 MPa for the first and second cycle, respectively; and severe water stress (SS) similar to MS, but with reference values of −1.6 and −2.5 MPa. In-between drought cycles, MS and SS trees were irrigated daily as the CTL trees until reaching Ψstem values similar to those of CTL trees. The MS and SS trees showed an important stomatal regulation and lower vegetative growth. The decreasing leaf turgor potential (Ψturgor) during the drought periods accounted for 40–100% of the reduction in leaf water potential at midday (Ψmd). The minimum osmotic potential for mature leaves was about 0.35 MPa lower than in well-irrigated trees. The occasional osmotic adjustment observed in MS and SS trees was not sufficient to maintain Ψturgor values similar to the CTL trees or to increase the specific leaf weight (SLW). The leaf insertion angle increased as the water stress level increased. Severe water stress (Ψstem < −2.0 MPa) resulted in clear early defoliation as a further step in water conservation.

Covering Norway spruce container seedlings with reflective shading cloth during field storage affects seedling post-planting growth

The field storage of container seedlings is often a necessity after the seedlings have been transported from nurseries close to the regeneration area. Suboptimal storage conditions can lead to reduced growth or even seedling mortality. Supporting favourable conditions for the seedlings during storage requires labour, especially for the watering of seedlings, and therefore increases the costs of forest regeneration. In this study, we examined the effects of covering Norway spruce container seedlings with a reflective shading cloth and neglecting the watering during field storage. This was done by measuring the drying of the seedlings during field storage, the rooting of the seedlings when planting, and the subsequent survival and performance in the field two and three growing seasons after planting. The study comprised one-year-old Norway spruce container seedlings covered with reflective shading cloth and seedlings with no cover (subject to rainfall) in 2012 and 2013; additionally, in 2013, replicates from both treatments were stored in conditions where rainfall was impeded. The stem water potential was measured, a rooting test was carried out, and the seedlings were planted in the test field weekly over 42 days of field storage without watering. As a novel finding, the results indicate that covering the seedlings with a reflective shading cloth during the field storage increased the risk of grey mould in summer storage and led to negative effects regarding post planting seedling development. The application of a shading cloth directly on the seedlings cannot be recommended to prolong the watering intervals during field storage in the current climatic conditions in Southern Finland, where the risk of grey mould is high.

Rootstock-Dependent Response of Hass Avocado to Salt Stress

Salt stress is a major limiting factor in avocado (Persea americana) cultivation, exacerbated by global trends towards scarcity of high-quality water for irrigation. Israeli avocado orchards have been irrigated with relatively high-salinity recycled municipal wastewater for over three decades, over which time rootstocks were selected for salt-tolerance. This study’s objective was to evaluate the physiological salt response of avocado as a function of the rootstock. We irrigated fruit-bearing ‘Hass’ trees grafted on 20 different local and introduced rootstocks with water high in salts (electrical conductivity of 1.4–1.5 dS/m). The selected rootstocks represent a wide range of genetic backgrounds, propagation methods, and horticultural characteristics. We investigated tree physiology and development during two years of salt exposure by measuring Cl and Na leaf concentrations, leaf osmolality, visible damages, trunk circumference, LAI, CO2 assimilation, stomatal conductance, spectral reflectance, stem water potential, trichomes density, and yield. We found a significant effect of the rootstocks on stress indicators, vegetative and reproductive development, leaf morphogenesis and photosynthesis rates. The most salt-sensitive rootstocks were VC 840, Dusa, and VC 802, while the least sensitive were VC 159, VC 140, and VC 152. We conclude that the rootstock strongly influences avocado tree response to salinity exposure in terms of physiology, anatomy, and development.