The physiology of drought stress in grapevine: towards an integrative definition of drought tolerance

Different frequencies of water deficit irrigation treatments improve fruit quality of Zitian seedless grapes under on-tree storage

In this study, we assessed the impact of varied water deficit irrigation frequencies (T1: 2.5 L/4 days; T2: 5 L/8 days; CK: 5 L/4 days) on Zitian Seedless grapes from veraison to post-ripening. Notably, total soluble solids increased during on-tree storage compared to at maturity, while total anthocyanin content decreased, particularly in CK (60.16%), T1 (62.35%), and less in T2 (50.54%). Glucose and fructose levels increased significantly in T1 and T2, more so in T2, but slightly declined in CK. Tartaric acid content increased by 41.42% in T2. Moreover, compared to regular irrigation, water deficit treatments enhanced phenolic metabolites and volatile compounds, including chlorogenic acid, various flavonoids, viniferin, hexanal, 2-nonenal, 2-hexen-1-ol, (E)-, 3-hydroxy-dodecanoic acid, and 1-hexanol, etc. Overall, the T2 treatment outperformed T1 and CK in maintaining grape quality. This study reveals that combining on-tree storage with water deficit irrigation not only improves grape quality but also water efficiency.

Carbon trade-offs in the fruits of fungus-tolerant Muscadinia × Vitis hybrids exposed to water deficit

Adopting disease-tolerant grapevines is an efficient option to implement a smarter management strategy limiting the environmental impacts linked to pesticide use. However, little is known on their production of fruit metabolites regarding expected future climate fluctuations, such as increased water shortage. Moreover, previous studies about how water deficit impacts grape composition, lack accuracy due to imprecise timing of fruit sampling. In this study, we phenotyped six new fungus-tolerant genotypes exposed to varying water status in field-grown conditions. The accumulation of water, main cations, primary and secondary metabolites were precisely monitored at the arrest of phloem unloading in fruits, which was targeted at the whole cluster level. The goal was to decipher the effects of both genotype and water deficit on the allocation of carbon into soluble sugars, organic acids, amino acids and anthocyanins. The results revealed that the effect of decreased water availability was specific to each berry component. While fruit sugar concentration remained relatively unaffected, the malic/tartaric acid balance varied based on differences among genotypes. Despite showing contrasted strategies on carbon allocation into berry metabolites, all genotypes reduced fruit yield and the amount of compounds of interest per plant under water deficit, with the extent of reduction being genotype-dependent and correlated with the response of berry volume to plant water status. This first set of data provides information to help reasoning the adaptation of these varieties according to the expected risks of drought and the possibilities of mitigating them through irrigation.

UV light and adaptive divergence of leaf physiology, anatomy, and ultrastructure drive heat stress tolerance in genetically distant grapevines

The genetic basis of plant response to light and heat stresses had been unveiled, and different molecular mechanisms of leaf cell homeostasis to keep high physiological performances were recognized in grapevine varieties. However, the ability to develop heat stress tolerance strategies must be further elucidated since the morpho-anatomical and physiological traits involved may vary with genotype × environment combination, stress intensity, and duration. A 3-year experiment was conducted on potted plants of Sardinian red grapevine cultivars Cannonau (syn. Grenache) and Carignano (syn. Carignan), exposed to prolonged heat stress inside a UV-blocking greenhouse, either submitted to low daily UV-B doses of 4.63 kJ m-2 d-1 (+UV) or to 0 kJ m-2 d-1 (-UV), and compared to a control (C) exposed to solar radiation (4.05 kJ m-2 d-1 average UV-B dose). Irrigation was supplied to avoid water stress, and canopy light and thermal microclimate were monitored continuously. Heat stress exceeded one-third of the duration inside the greenhouse and 6% in C. In vivo spectroscopy, including leaf reflectance and fluorescence, allowed for characterizing different patterns of leaf traits and metabolites involved in oxidative stress protection. Cannonau showed lower stomatal conductance under C (200 mmol m-2 s-1) but more than twice the values inside the greenhouse (400 to 900 mmol m-2 s-1), where water use efficiency was reduced similarly in both varieties. Under severe heat stress and -UV, Cannonau showed a sharper decrease in primary photochemical activity and higher leaf pigment reflectance indexes and leaf mass area. UV-B increased the leaf pigments, especially in Carignano, and different leaf cell regulatory traits to prevent oxidative damage were observed in leaf cross-sections. Heat stress induced chloroplast swelling, plastoglobule diffusion, and the accumulation of secretion deposits in both varieties, aggravated in Cannonau -UV by cell vacuolation, membrane dilation, and diffused leaf blade spot swelling. Conversely, in Carignano UV-B, cell wall barriers and calcium oxalate crystals proliferated in mesophyll cells. These responses suggest an adaptive divergence among cultivars to prolonged heat stress and UV-B light. Further research on grapevine biodiversity, heat, and UV-B light interactions may give new insights on the extent of stress tolerance to improve viticulture adaptive strategies in climate change hotspots.

Biochemical analysis of three red grapevine varieties during three phenological periods grown under Mediterranean climate conditions

In Mediterranean regions, severe summers are becoming more common, leading to restrictions to vine productivity and yield quality, requiring sustainable practices to support this sector. We assessed the behaviour of three red grapevine varieties from the Douro Region to examine their tolerance to summer climate stress from the perspective that the less common varieties may have potential for increased use in a climate change scenario. Leaf and fruit biochemical profile, antioxidant activity and fruit colorimetric parameters were assessed at different phenological stages in Aragonez (AR), Tinto Cão (TC) and Touriga Nacional (TN) grape varieties. All three varieties exhibit significant variability in phenological timing, influenced by genetic and environmental factors. Photosynthetic pigment strategies differed among varieties. Chlorophyll content in AR was high to cope with high radiation, while TN displaying a balanced approach, and TC had lower pigment levels, with higher levels of phenolics, antioxidants, and soluble sugars, particularly during stress. The variations in berry biochemical profile highlight the distinct characteristics of the varieties. TC and TN show potential for coping with climate change, having elevated total acidity, while AR has larger and heavier berries with distinct coloration. These findings reinforce the need to study the behaviour of different varieties in each Terroir, to understand their diverse strategies to deal with summer climate stress. This will help in selecting the most suitable variety for these conditions under vineyard management in the Douro Region.

Smart selection of soil microbes for resilient and sustainable viticulture

The grapevine industry is of high economic importance in several countries worldwide. Its growing market demand led to an acceleration of the entire production processes, implying increasing use of water resources at the expense of environmental water balance and the hydrological cycle. Furthermore, in recent decades climate change and the consequent expansion of drought have further compromised water availability, making current agricultural systems even more fragile from ecological and economical perspectives. Consequently, farmers' income and welfare are increasingly unpredictable and unstable. Therefore, it is urgent to improve the resilience of vineyards, and of agro-ecosystems in general, by developing sustainable and environmentally friendly farming practices by more rational biological and natural resources use. The PRIMA project PROSIT addresses these challenges by characterizing and harnessing grapevine-associated microbiota to propose innovative and sustainable agronomic practices. PROSIT aims to determine the efficacy of natural microbiomes transferred from grapevines adapted to arid climate to commonly cultivated grapevine cultivars. In doing so it will test those natural microbiome effects on drought tolerance. This multidisciplinary project will utilize in vitro culture techniques, bioimaging, microbiological tests, metabolomics, metabarcoding and epigenetic analyses. These will be combined to shed light on molecular mechanisms triggered in plants by microbial associations upon water stress. To this end it is hoped that the project will serve as a blueprint not only for studies uncovering the microbiome role in drought stress in a wide range of species, but also for analyzing its effect on a wide range of stresses commonly encountered in modern agricultural systems.

Canopy Architecture and Sun Exposure Influence Berry Cluster-Water Relations in the Grapevine Variety Muscat of Alexandria

Climate-change-related increases in the frequency and intensity of heatwaves affect viticulture, leading to losses in yield and grape quality. We assessed whether canopy-architecture manipulation mitigates the effects of summer stress in a Mediterranean vineyard. The Vitis vinifera L variety Muscat of Alexandria plants were monitored during 2019-2020. Two canopy shoot-positioning treatments were applied: vertical shoot positioning (VSP) and modulated shoot positioning (MSP). In MSP, the west-side upper foliage was released to promote partial shoot leaning, shading the clusters. Clusters were sampled at pea size (PS), veraison (VER), and full maturation (FM). Measurements included rachis anatomy and hydraulic conductance (Kh) and aquaporins (AQP) and stress-related genes expression in cluster tissues. The results show significant seasonal and interannual differences in Kh and vascular anatomy. At VER, the Kh of the rachis and rachis+pedicel and the xylem diameter decreased but were unaffected by treatments. The phloem-xylem ratio was either increased (2019) or reduced (2020) in MSP compared to VSP. Most AQPs were down-regulated at FM in pedicels and up-regulated at VER in pulp. A potential maturation shift in MSP was observed and confirmed by the up-regulation of several stress-related genes in all tissues. The study pinpoints the role of canopy architecture in berry-water relations and stress response during ripening.

Pre-inoculation water deficit effects on grapevine physiology, Xylella fastidiosa titers, and Pierce's disease progression

Drought and Pierce's disease are common throughout many grapevine-growing regions such as Mexico and the United States. Yet, how ongoing water deficits affect infections of Xylella fastidiosa, the causal agent of Pierce's disease, is poorly understood. Symptoms were observed to be significantly more severe in water-stressed plants one month after X. fastidiosa inoculation, and, in one experiment, titers were significantly lower in water-stressed than well-watered grapevines. Host chemistry examinations revealed overall amino acid and phenolic levels did not statistically differ due to water deficits, but sugar levels were significantly greater in water stressed than well-watered plants. Results highlight the need to especially manage Pierce's disease spread in grapevines experiencing drought.

Phloem anatomy predicts berry sugar accumulation across 13 wine-grape cultivars

Introduction

Climate change is impacting the wine industry by accelerating ripening processes due to warming temperatures, especially in areas of significant grape production like California. Increasing temperatures accelerate the rate of sugar accumulation (measured in ⁰Brix) in grapes, however this presents a problem to wine makers as flavor profiles may need more time to develop properly. To alleviate the mismatch between sugar accumulation and flavor compounds, growers may sync vine cultivars with climates that are most amenable to their distinct growing conditions. However, the traits which control such cultivar specific climate adaptation, especially for ⁰Brix accumulation rate, are poorly understood. Recent studies have shown that higher rates of fruit development and sugar accumulation are predicted by larger phloem areas in different organs of the plant.

Methods

Here we test this phloem area hypothesis using a common garden experiment in the Central Valley of Northern California using 18 cultivars of the common grapevine (Vitis vinifera) and assess the grape berry sugar accumulation rates as a function of phloem area in leaf and grape organs.

Results

We find that phloem area in the leaf petiole organ as well as the berry pedicel is a significant predictor of ⁰Brix accumulation rate across 13 cultivars and that grapes from warm climates overall have larger phloem areas than those from hot climates. In contrast, other physiological traits such as photosynthetic assimilation and leaf water potential did not predict berry accumulation rates.

Discussion

As hot climate cultivars have lower phloem areas which would slow down brix accumulation, growers may have inadvertently been selecting this trait to align flavor development with sugar accumulation across the common cultivars tested. This work highlights a new trait that can be easily phenotyped (i.e., petiole phloem area) and be used for growers to match cultivar more accurately with the temperature specific climate conditions of a growing region to obtain satisfactory sugar accumulation and flavor profiles.

A Better Fruit Quality of Grafted Blueberry Than Own-Rooted Blueberry Is Linked to Its Anatomy

To further clarify the impact of different rootstocks in grafted blueberry, fruit quality, mineral contents, and leaf gas exchange were investigated in 'O'Neal' blueberry (Vaccinium corymbosum) grafted onto 'Anna' (V. corymbosum) (AO), 'Sharpblue' (V. corymbosum) (SO), 'Baldwin' (V. virgatum) (BO), 'Plolific' (V. virgatum) (PO), and 'Tifblue' (V. virgatum) (TO) rootstocks and own-rooted 'O'Neal' (NO), and differences in anatomic structures and drought resistance were determined in AO, TO, and NO. The findings revealed that fruit quality in TO and PO was excellent, that of BO and SO was good, and that of AO and NO was medium. 'Tifblue' and 'Plolific' rootstocks significantly increased the levels of leaf phosphorus and net photosynthetic rate of 'O'Neal', accompanied by a synchronous increase in their transpiration rates, stomatal conductance, and intercellular CO2. Additionally, the comprehensive evaluation scores from a principal component analysis based on anatomic structure traits from high to low were in the order TO > AO > NO. The P50 (xylem water potential at 50% loss of hydraulic conductivity) values of these grafted plants descended in the order NO > AO > TO, and the branch hydraulic conductivity of TO and sapwood hydraulic conductivity of TO and AO were significantly lower than those of NO. Thus, TO plants exhibited the strongest drought resistance, followed by AO, and NO, and this trait was related to the effects of different rootstocks on the fruit quality of 'O'Neal' blueberry. These results provided a basis for a deeper understanding of the interaction between rootstocks and scions, as well mechanisms to improve blueberry fruit quality.

Emerging Roles of Epigenetics in Grapevine and Winegrowing

Epigenetics refers to dynamic chemical modifications to the genome that can perpetuate gene activity without changes in the DNA sequence. Epigenetic mechanisms play important roles in growth and development. They may also drive plant adaptation to adverse environmental conditions by buffering environmental variation. Grapevine is an important perennial fruit crop cultivated worldwide, but mostly in temperate zones with hot and dry summers. The decrease in rainfall and the rise in temperature due to climate change, along with the expansion of pests and diseases, constitute serious threats to the sustainability of winegrowing. Ongoing research shows that epigenetic modifications are key regulators of important grapevine developmental processes, including berry growth and ripening. Variations in epigenetic modifications driven by genotype-environment interplay may also lead to novel phenotypes in response to environmental cues, a phenomenon called phenotypic plasticity. Here, we summarize the recent advances in the emerging field of grapevine epigenetics. We primarily highlight the impact of epigenetics to grapevine stress responses and acquisition of stress tolerance. We further discuss how epigenetics may affect winegrowing and also shape the quality of wine.

The legacy of past droughts induces water-sparingly behaviour in Grüner Veltliner grapevines

Drought is becoming more frequent and severe in numerous wine-growing regions. Nevertheless, limited research has examined the legacy of recurrent droughts, focusing on leaf physiology and anatomy over consecutive seasons. We investigated drought legacies (after 2 years of drought exposure) in potted grapevines, focusing on stomatal behaviour under well-watered conditions during the third year. Vines were subjected for two consecutive years to short- (SD) or long-term (LD) seasonal droughts, or well-watered conditions (WW). In the third year, all plants were grown without water limitation. Water potential and gas exchange were monitored throughout the three seasons, while leaf morpho-anatomical traits were measured at the end of the third year. During droughts (1st and 2nd year), stem water potential of SD and LD plants fell below -1.1 MPa, with a consequent 75% reduction in stomatal conductance (gs ) compared to WW. In the 3rd year, when all vines were daily irrigated to soil capacity (midday stem water potential ~ -0.3 MPa), 45% lower values of gs were observed in the ex-LD group compared to both ex-SD and ex-WW. Reduced midrib vessel diameter, lower leaf theoretical hydraulic conductivity, and smaller stomata were measured in ex-LD leaves compared to ex-SD and ex-WW, likely contributing to the reduced gas exchange. Our findings suggest that grapevines exposed to drought may adopt a more water-conserving strategy in subsequent seasons, irrespective of current soil water availability, with the degree of change influenced by the intensity and duration of past drought events.

TgLUT1 regulated by TgWRKY10 enhances the tolerance of Torreya grandis to drought stress

Drought stress is a major abiotic stress which severely reduces the plant growth and limits agricultural productivity. Previous studies have demonstrated that lutein directly synthesized by the carotenoid epsilon-ring hydroxylase gene (LUT1) played crucial roles in regulating drought response. Notwithstanding the myriad studies on LUT1's response to drought stress in certain plant species such as Arabidopsis, the precise function mechanisms within tree species remain ambiguously understood. Our study reveals that under drought stress, TgLUT1, a novel LUT gene instrumental in β-lutein biosynthesis, was markedly up-regulated in Torreya grandis. Subcellular localization assay indicated that TgLUT1 protein was localized to chloroplasts. Phenotypic analysis showed that overexpression of TgLUT1 enhanced the tolerance of tomato to drought stress. Overexpressing of TgLUT1 increased the values of maximal photochemical efficiency of photosystem II (Fv/Fm), net photosynthetic rate (Pn) and non-photochemical quenching (NPQ), and reduced the accumulation of hydrogen peroxide (H2O2), malondialdehyde (MDA) content and electrolyte leakage percentage in response to drought stress. Furthermore, overexpression of TgLUT1 decreased the stomatal conductance to reduce the water loss rate exposed to drought stress. In addition, yeast one-hybrid assay, dual luciferase assay system and qRT-PCR results showed that TgWRKY10 down-regulated by drought stress inhibited the expression of TgLUT1 by directly binding to the TgLUT1 promoter. Collectively, our results show that TgWRKY10, down-regulated by drought stress, negatively regulates the expression of TgLUT1 to modulate the drought stress response. This study contributes to a more comprehensive understanding of LUT1's function in the stress responses of economically significant forest plants.

Combining Genetic and Phenotypic Analyses for Detecting Bread Wheat Genotypes of Drought Tolerance through Multivariate Analysis Techniques

Successfully promoting drought tolerance in wheat genotypes will require several procedures, such as field experimentations, measuring relevant traits, using analysis tools of high precision and efficiency, and taking a complementary approach that combines analyses of phenotyping and genotyping at once. The aim of this study is to assess the genetic diversity of 60 genotypes using SSR (simple sequence repeat) markers collected from several regions of the world and select 13 of them as more genetically diverse to be re-evaluated under field conditions to study drought stress by estimating 30 agro-physio-biochemical traits. Genetic parameters and multivariate analysis were used to compare genotype traits and identify which traits are increasingly efficient at detecting wheat genotypes of drought tolerance. Hierarchical cluster (HC) analysis of SSR markers divided the genotypes into five main categories of drought tolerance: four high tolerant (HT), eight tolerant (T), nine moderate tolerant (MT), six sensitive (S), and 33 high sensitive (HS). Six traits exhibit a combination of high heritability (>60%) and genetic gain (>20%). Analyses of principal components and stepwise multiple linear regression together identified nine traits (grain yield, flag leaf area, stomatal conductance, plant height, relative turgidity, glycine betaine, polyphenol oxidase, chlorophyll content, and grain-filling duration) as a screening tool that effectively detects the variation among the 13 genotypes used. HC analysis of the nine traits divided genotypes into three main categories: T, MT, and S, representing three, five, and five genotypes, respectively, and were completely identical in linear discriminant analysis. But in the case of SSR markers, they were classified into three main categories: T, MT, and S, representing five, three, and five genotypes, respectively, which are both significantly correlated as per the Mantel test. The SSR markers were associated with nine traits, which are considered an assistance tool in the selection process for drought tolerance. So, this study is useful and has successfully detected several agro-physio-biochemical traits, associated SSR markers, and some drought-tolerant genotypes, coupled with our knowledge of the phenotypic and genotypic basis of wheat genotypes.

Genetic and Epigenetic Responses of Autochthonous Grapevine Cultivars from the 'Epirus' Region of Greece upon Consecutive Drought Stress

Within the framework of preserving and valorizing the rich grapevine germplasm of the Epirus region of Greece, indigenous grapevine (Vitis vinifera L.) cultivars were characterized and assessed for their resilience to abiotic stresses in the context of climate change. The cultivars 'Debina' and 'Dichali' displayed significant differences in their response to drought stress as judged by morpho-physiological analysis, indicating higher drought tolerance for Dichali. Hence, they were selected for further study aiming to identify genetic and epigenetic mechanisms possibly regulating drought adaptability. Specifically, self-rooted and heterografted on 'Richter 110' rootstock plants were subjected to two phases of drought with a recovery period in between. Gene expression analysis was performed for two stress-related miRNAs and their target genes: (a) miRNA159 and putative targets, VvMYB101, VvGATA-26-like, VvTOPLESS-4-like and (b) miRNA156 and putative target gene VvCONSTANS-5. Overall, grafted plants exhibited a higher drought tolerance than self-rooted plants, suggesting beneficial rootstock-scion interactions. Comparative analysis revealed differential gene expression under repetitive drought stresses between the two cultivars as well as between the self-rooted and grafted plants. 'Dichali' exhibited an up-regulation of most of the genes examined, which may be associated with increased tolerance. Nevertheless, the profound down-regulation of VvTOPLESS-4-like (a transcriptional co-repressor of transcription factors) upon drought and the concomitant up-regulation of miRNA159 highlights the importance of this 'miRNA-target' module in drought responsiveness. DNA methylation profiling using MSAP analysis revealed differential methylation patterns between the two genotypes in response to drought. Further investigations of gene expression and DNA methylation will contribute to our understanding of the epigenetic mechanisms underlying grapevine tolerance to drought stress.

The role of environmental stress in fruit pigmentation

For many fruit crops, the colour of the fruit outwardly defines its eating quality. Fruit pigments provide reproductive advantage for the plant as well as providing protection against unfavourable environmental conditions and pathogens. For consumers these colours are considered attractive and provide many of the dietary benefits derived from fruits. In the majority of species, the main pigments are either carotenoids and/or anthocyanins. They are produced in the fruit as part of the ripening process, orchestrated by phytohormones and an ensuing transcriptional cascade, culminating in pigment biosynthesis. Whilst this is a controlled developmental process, the production of pigments is also attuned to environmental conditions such as light quantity and quality, availability of water and ambient temperature. If these factors intensify to stress levels, fruit tissues respond by increasing (or ceasing) pigment production. In many cases, if the stress is not severe, this can have a positive outcome for fruit quality. Here, we focus on the principal environmental factors (light, temperature and water) that can influence fruit colour.

Cessation of berry growth coincides with leaf complete stomatal closure at pre-veraison for grapevine (Vitis vinifera) subjected to progressive drought stress

BACKGROUND AND AIMS

Drought events have devasting impacts on grape berry production. The aim of this study was to investigate berry growth in the context of leaf stomatal closure under progressive drought stress.

METHODS

Potted grapevine plants (varieties 'Syrah' and 'Cabernet Sauvignon') were evaluated at pre-verasion (30-45 d after anthesis, DAA) and post-veraison (90-107 DAA). Berry diameter, berry absolute growth rate (AGR), leaf stomatal conductance (Gs) at midday, plant water potential at predawn and midday (ΨPD and ΨMD, respectively), and soil relative water content were measured repeatedly. The ΨPD-threshold of 90 % loss in stomatal conductance (Gs10, i.e. complete stomatal closure) was determined. Data were related to plant dehydration phases I, II and III with corresponding boundaries Θ1 and Θ2, using the water potential curve method.

KEY RESULTS

At pre-veraison, berry AGR declined together with leaf Gs in response to soil drying in both varieties. Berry AGR transitioned from positive to negative (shrinkage) values when leaf Gs approached zero. The Gs10-threshold was -0.81 MPa in 'Syrah' and -0.74 MPa in 'Cabernet Sauvignon' and was linked to boundary Θ1. At post-veraison, berry AGR was negligible and negative AGR values were not intensified by increasing drought stress in either variety.

CONCLUSION

Leaf complete stomatal closure under progressive drought stress coincides with cessation of berry growth followed by shrinkage at pre-veraison (growth stage 1).

Effects of Vine Water Status on Malate Metabolism and γ-Aminobutyric Acid (GABA) Pathway-Related Amino Acids in Marselan (Vitis vinifera L.) Grape Berries

Malic acid is the predominant organic acid in grape berries, and its content is affected by abiotic factors such as temperature (fruit zone microclimate) and water (vine water status). The objectives of this study were to explore the potential mechanisms behind the effects of vine water status on the biosynthesis and degradation of berry malic acid and the potential downstream effects on berry metabolism. This study was conducted over two growing seasons in 2021 and 2022, comprising three watering regimes: no water stress (CK), light water stress (LWS), and moderate water stress (MWS). Compared to CK, a significantly higher level of malic acid was found in berries from the MWS treatment when the berry was still hard and green (E-L 33) in both years. However, water stress reduced the malic acid content at the ripe berry harvest (E-L 38) stage. The activities of NAD-malate dehydrogenase (NAD-MDH) and pyruvate kinase (PK) were enhanced by water stress. Except for the E-L 33 stage, the activity of phosphoenolpyruvate carboxylase (PEPC) was reduced by water stress. The highest phosphoenolpyruvate carboxykinase (PEPCK) activity was observed at the berry veraison (E-L 35) stage and coincided with the onset of a decrease in the malate content. Meanwhile, the expression of VvPEPCK was consistent with its enzyme activity. This study showed that water stress changed the content of some free amino acids (GABA, proline, leucine, aspartate, and glutamate), two of which (glutamate and GABA) are primary metabolites of the GABA pathway.

Rapid leaf xylem acclimation diminishes the chances of embolism in grapevines

Under most conditions tight stomatal regulation in grapevines (Vitis vinifera) avoids xylem embolism. The current study evaluated grapevine responses to challenging scenarios that might lead to leaf embolism and consequential leaf damage. We hypothesized that embolism would occur if the vines experienced low xylem water potential (Ψx) shortly after bud break or later in the season under a combination of extreme drought and heat. We subjected vines to two potentially dangerous environments: (i) withholding irrigation from a vineyard grown in a heatwave-prone environment, and (ii) subjecting potted vines to terminal drought 1 month after bud break. In the field experiment, a heatwave at the beginning of August resulted in leaf temperatures over 45 °C. However, effective stomatal response maintained the xylem water potential (Ψx) well above the embolism threshold, and no leaf desiccation was observed. In the pot experiment, leaves of well-watered vines in May were relatively vulnerable to embolism with 50% embolism (P50) at -1.8 MPa. However, when exposed to drought, these leaves acclimated their leaf P50 by 0.65 MPa in less than a week and before reaching embolism values. When dried to embolizing Ψx, the leaf damage proportion matched (percentage-wise) the leaf embolism level. Our findings indicate that embolism and leaf damage are usually avoided by the grapevines' efficient stomatal regulation and rapid acclimation of their xylem vulnerability.

Biochemical Response and Gene Expression to Water Deficit of Croatian Grapevine Cultivars (Vitis vinifera L.) and a Specimen of Vitis sylvestris

The biochemical response and gene expression in different grapevine cultivars to water deficit are still not well understood. In this study, we investigated the performance of four traditional Croatian Vitis vinifera L. cultivars ('Plavac mali crni', 'Istrian Malvasia', 'Graševina', and 'Tribidrag'), and one wild (Vitis vinifera subsp. sylvestris) genotype exposed to water deficit (WD) for nine days under semi-controlled conditions in the greenhouse. Sampling for biochemical and gene expression analyses was performed at days six and nine from the beginning of WD treatment. The WD affected the accumulation of metabolites with a significant increase in abscisic acid (ABA), salicylic acid (SA), and proline in the leaves of the stressed genotypes when the WD continued for nine days. Lipid peroxidation (MDA) was not significantly different from that of the control plants after six days of WD, whereas it was significantly lower (297.40 nmol/g dw) in the stressed plants after nine days. The cultivar 'Istrian Malvasia' responded rapidly to the WD and showed the highest and earliest increase in ABA levels (1.16 ng mg-1 dw, i.e., 3.4-fold increase compared to control). 'Graševina' differed significantly from the other genotypes in SA content at both time points analyzed (six and nine days, 47.26 and 49.63 ng mg-1 dw, respectively). Proline level increased significantly under WD (up to 5-fold at day nine), and proline variation was not genotype driven. The expression of aquaporin genes (TIP2;1 and PIP2;1) was down-regulated in all genotypes, coinciding with the accumulation of ABA. The gene NCED1 (9-cis-epoxycarotenoid dioxygenase) related to ABA was up-regulated in all genotypes under stress conditions and served as a reliable marker of drought stress. This work suggests that the stress response in metabolite synthesis and accumulation is complex, treatment- and genotype-dependent.

Variations in amino acids caused by drought stress mediate the predisposition of Carya cathayensis to Botryosphaeria canker disease

Abiotic stresses can affect the outcome of plant-pathogen interactions, mostly by predisposing the host plant to infection; however, the crosstalk between pathogens and plants related to such predisposition remains unclear. Here, we investigated the predisposition of Carya cathayensis to infection by the fungal pathogen Botryosphaeria dothidea (Bd) caused by drought in the host plant. High levels of drought stress resulted in a significant increase in plant susceptibility to Bd. Drought significantly induced the accumulation of H2O2 and the free amino acids Pro, Leu, and Ile, and in the phloem tissues of plants, and decreased the content of non-structural carbohydrates. In vitro assays showed that Bd was sensitive to H2O2; however, Pro played a protective role against exogenous H2O2. Leu, Ile, and Pro induced asexual reproduction of Bd. Our results provide the first analysis of how drought predisposes C. cathayensis to Botrysphaeria canker via amino acid accumulation in the host plant, and we propose a model that integrates the plant-pathogen interactions involved.

Effect of Drought on the Future Sugar Content of Wine Grape Varieties till 2100: Possible Adaptation in the Hungarian Eger Wine Region

The most significant risk for viticulture is that the sugar content of the grapes will increase in the future due to rising temperatures. As a result, it will be possible to produce wines with increasing alcohol content in the future. Excessively high alcohol content can significantly reduce the wines' marketability and viticulture's profitability. Our study seeks to answer how the expected drought in the Southern and Central regions of Europe will affect the future change in the sugar content of grapes. The degree of dryness was examined using the dryness index in the study. Finally, it was analyzed how the dryness index affects the past and future occurrence of maximum sugar content for six grape varieties. The probability of the occurrence of maximum sugar content for most vine grape varieties will decrease in the near future. However, in the distant future, there is a likelihood that the occurrence of maximum sugar content will increase again. If we can maintain the DI ≥ -10 condition with regulated deficit irrigation, the probability of the occurrence of maximum sugar content may decrease significantly in the near future. Ensuring moderate dryness is the only way to achieve the proper sugar content.

Best Procedures for Leaf and Stem Water Potential Measurements in Grapevine: Cultivar and Water Status Matter

The pressure chamber is the most used tool for plant water status monitoring. However, species/cultivar and seasonal effects on protocols for reliable water potential determination have not been properly tested. In four grapevine cultivars and two times of the season (early season, Es; late season, Ls, under moderate drought), we assessed the maximum sample storage time before leaf water potential (Ψ_leaf) measurements and the minimum equilibration time for stem water potential (Ψ_stem) determination, taking 24 h leaf cover as control. In 'Pinot gris', Ψ_leaf already decreased after 1 h leaf storage in both campaigns, dropping by 0.4/0.5 MPa after 3 h, while in 'Refosk', it decreased by 0.1 MPa after 1 and 2 h in Es and Ls, respectively. In 'Merlot' and 'Merlot Kanthus', even 3 h storage did not affect Ψ_leaf. In Es, the minimum Ψ_stem equilibration was 1 h for 'Refošk' and 10 min for 'Pinot gris' and 'Merlot'. In Ls, 'Merlot Kanthus' required more than 2 h equilibration, while 1 h to 10 min was sufficient for the other cultivars. The observed cultivar and seasonal differences indicate that the proposed tests should be routinely performed prior to experiments to define ad hoc procedures for water status determination.

Impact of heat stress, water stress, and their combined effects on the metabolism and transcriptome of grape berries

Recurring heat and drought episodes present challenges to the sustainability of grape production worldwide. We investigated the impacts of heat and drought stress on transcriptomic and metabolic responses of berries from two wine grape varieties. Cabernet Sauvignon and Riesling grapevines were subjected to one of four treatments during early fruit ripening: (1) drought stress only, (2) heat stress only, (3) simultaneous drought and heat stress, (4) no drought or heat stress (control). Berry metabolites, especially organic acids, were analyzed, and time-course transcriptome analysis was performed on samples before, during, and after the stress episode. Both alone and in conjunction with water stress, heat stress had a much more significant impact on berry organic acid content, pH, and titratable acidity than water stress. This observation contrasts with previous reports for leaves, which responded more strongly to water stress, indicating that grape berries display a distinct, organ-specific response to environmental stresses. Consistent with the metabolic changes, the global transcriptomic analysis revealed that heat stress had a more significant impact on gene expression in grape berries than water stress in both varieties. The differentially expressed genes were those associated with the tricarboxylic acid cycle and glyoxylate cycle, mitochondrial electron transport and alternative respiration, glycolysis and gluconeogenesis, carbohydrate allocation, ascorbate metabolism, and abiotic stress signaling pathways. Knowledge regarding how environmental stresses, alone and in combination, impact the berry metabolism of different grape varieties will form the basis for developing recommendations for climate change mitigation strategies and genetic improvement.

Screening and evaluation of drought resistance traits of winter wheat in the North China Plain

Background

Drought-resistant varieties are an important way to address the conflict between wheat's high water demand and the scarcity of water resources in the North China Plain (NCP). Drought stress impacts many morphological and physiological indicators in winter wheat. To increase the effectiveness of breeding drought-tolerant varieties, choosing indices that can accurately indicate a variety's drought resistance is advantageous.

Results

From 2019 to 2021, 16 representative winter wheat cultivars were cultivated in the field, and 24 traits, including morphological, photosynthetic, physiological, canopy, and yield component traits, were measured to evaluate the drought tolerance of the cultivars. Principal component analysis (PCA) was used to transform 24 conventional traits into 7 independent, comprehensive indices, and 10 drought tolerance indicators were screened out by regression analysis. The 10 drought tolerance indicators were plant height (PH), spike number (SN), spikelet per spike(SP), canopy temperature (CT), leaf water content (LWC), photosynthetic rate (A), intercellular CO2 concentration (Ci), peroxidase activity (POD), malondialdehyde content (MDA), and abscisic acid (ABA). In addition, through membership function and cluster analysis, 16 wheat varieties were divided into 3 categories: drought-resistant, drought weak sensitive, and drought-sensitive.

Conclusion

JM418, HM19,SM22, H4399, HG35, and GY2018 exhibited excellent drought tolerance and,therefore, can be used as ideal references to study the drought tolerance mechanism in wheat and breeding drought-tolerant wheat cultivars.

Functional Differences of Grapevine Circular RNA Vv-circPTCD1 in Arabidopsis and Grapevine Callus under Abiotic Stress

Circular RNAs (circRNAs) serve as covalently closed single-stranded RNAs and have been proposed to influence plant development and stress resistance. Grapevine is one of the most economically valuable fruit crops cultivated worldwide and is threatened by various abiotic stresses. Herein, we reported that a circRNA (Vv-circPTCD1) processed from the second exon of the pentatricopeptide repeat family gene PTCD1 was preferentially expressed in leaves and responded to salt and drought but not heat stress in grapevine. Additionally, the second exon sequence of PTCD1 was highly conserved, but the biogenesis of Vv-circPTCD1 is species-dependent in plants. It was further found that the overexpressed Vv-circPTCD1 can slightly decrease the abundance of the cognate host gene, and the neighboring genes are barely affected in the grapevine callus. Furthermore, we also successfully overexpressed the Vv-circPTCD1 and found that the Vv-circPTCD1 deteriorated the growth during heat, salt, and drought stresses in Arabidopsis. However, the biological effects on grapevine callus were not always consistent with those of Arabidopsis. Interestingly, we found that the transgenic plants of linear counterpart sequence also conferred the same phenotypes as those of circRNA during the three stress conditions, no matter what species it is. Those results imply that although the sequences are conserved, the biogenesis and functions of Vv-circPTCD1 are species-dependent. Our results indicate that the plant circRNA function investigation should be conducted in homologous species, which supports a valuable reference for further plant circRNA studies.

Quantifying the grapevine xylem embolism resistance spectrum to identify varieties and regions at risk in a future dry climate

Maintaining wine production under global warming partly relies on optimizing the choice of plant material for a given viticultural region and developing drought-resistant cultivars. However, progress in these directions is hampered by the lack of understanding of differences in drought resistance among Vitis genotypes. We investigated patterns of xylem embolism vulnerability within and among 30 Vitis species and sub-species (varieties) from different locations and climates, and assessed the risk of drought vulnerability in 329 viticultural regions worldwide. Within a variety, vulnerability to embolism decreased during summer. Among varieties, we have found wide variations in drought resistance of the vascular system in grapevines. This is particularly the case within Vitis vinifera, with varieties distributed across four clusters of embolism vulnerability. Ugni blanc and Chardonnay featured among the most vulnerable, while Pinot noir, Merlot and Cabernet Sauvignon ranked among the most resistant. Regions possibly at greater risk of being vulnerable to drought, such as Poitou-Charentes, France and Marlborough, New Zealand, do not necessarily have arid climates, but rather bear a significant proportion of vulnerable varieties. We demonstrate that grapevine varieties may not respond equally to warmer and drier conditions, and highlight that hydraulic traits are key to improve viticulture suitability under climate change.

Wind speed, sun exposure and water status alter sunburn susceptibility of grape berries

In the context of climate change, yield and quality losses from sunburn necrosis are challenging grape growers around the world. In a previous review, we identified the role of wind speed, duration of heat exposure, drought stress and adaptation as major knowledge gaps that prevent a better predictability of sunburn events. In this paper we present results of targeted experiments aiming to close these knowledge gaps. The effects of drought stress and adaptation on sunburn susceptibility were investigated in a combined drought stress/ defoliation experiment. Riesling grapevines growing in an arid climate were fully irrigated or drought stressed, and clusters were exposed to sunlight by fruit-zone leaf removal (defoliation) at two developmental stages. Sunburn symptoms were induced using infrared heaters while fruit surface temperature was measured using thermal imaging enabling the establishment of threshold temperatures. The influence of the duration of heat exposure of berries was examined by heating grape clusters to a stable temperature and monitoring the evolution of sunburn symptoms over time. To examine the effects of wind speed on the appearance of sunburn necrosis symptoms, fruit surface temperatures and sunburn severity were measured along an artificially induced wind speed gradient in two cultivars using thermal imaging and visual inspection. Longer durations of heat exposure required lower fruit surface temperatures to induce damage, while the differences in temperature after 60 min and 90 min of exposure were marginal (47.82 ± 0.25 °C and 47.06 ± 0.26 °C). Clusters of vines grown under water deficit were less susceptible to sunburn compared to those of well-irrigated plants following defoliation. The lethal temperature of clusters exposed to sunlight for seven days did not differ from those exposed to sunlight for 28 days, indicating that a full adaptation ocurred within this period. Higher wind speeds led to lower cluster temperatures and reduced sunburn severity. First evidence of a drought priming induced heat tolerance of grapevine berries was found, while adaptation had a more pronounced effect on the susceptibility to sunburn compared to water stress.

Drought stress in 'Shine Muscat' grapevine: Consequences and a novel mitigation strategy-5-aminolevulinic acid

Drought is a common and serious abiotic stress in viticulture, and it is urgent to select effective measures to alleviate it. The new plant growth regulator 5-aminolevulinic acid (ALA) has been utilized to alleviate abiotic stresses in agriculture in recent years, which provided a novel idea to mitigate drought stress in viticulture. The leaves of 'Shine Muscat' grapevine (Vitis vinifera L.) seedlings were treated with drought (Dro), drought plus 5-aminolevulinic acid (ALA, 50 mg/L) (Dro_ALA) and normal watering (Control) to clarify the regulatory network used by ALA to alleviate drought stress in grapevine. Physiological indicators showed that ALA could effectively reduce the accumulation of malondialdehyde (MDA) and increase the activities of peroxidase (POD) and superoxide dismutase (SOD) in grapevine leaves under drought stress. At the end of treatment (day 16), the MDA content in Dro_ALA was reduced by 27.63% compared with that in Dro, while the activities of POD and SOD reached 2.97- and 5.09-fold of those in Dro, respectively. Furthermore, ALA reduces abscisic acid by upregulating CYP707A1, thus, relieving the closure of stomata under drought. The chlorophyll metabolic pathway and photosynthetic system are the major pathways affected by ALA to alleviate drought. Changes in the genes of chlorophyll synthesis, including CHLH, CHLD, POR, and DVR; genes related to degradation, such as CLH, SGR, PPH and PAO; the RCA gene that is related to Rubisco; and the genes AGT1 and GDCSP related to photorespiration form the basis of these pathways. In addition, the antioxidant system and osmotic regulation play important roles that enable ALA to maintain cell homeostasis under drought. The reduction of glutathione, ascorbic acid and betaine after the application of ALA confirmed the alleviation of drought. In summary, this study revealed the mechanism of effects of drought stress on grapevine, and the alleviating effect of ALA, which provides a new concept to alleviate drought stress in grapevine and other plants.

Towards grapevine root architectural models to adapt viticulture to drought

To sustainably adapt viticultural production to drought, the planting of rootstock genotypes adapted to a changing climate is a promising means. Rootstocks contribute to the regulation of scion vigor and water consumption, modulate scion phenological development and determine resource availability by root system architecture development. There is, however, a lack of knowledge on spatio-temporal root system development of rootstock genotypes and its interactions with environment and management that prevents efficient knowledge transfer into practice. Hence, winegrowers take only limited advantage of the large variability of existing rootstock genotypes. Models of vineyard water balance combined with root architectural models, using both static and dynamic representations of the root system, seem promising tools to match rootstock genotypes to frequently occurring future drought stress scenarios and address scientific knowledge gaps. In this perspective, we discuss how current developments in vineyard water balance modeling may provide the background for a better understanding of the interplay of rootstock genotypes, environment and management. We argue that root architecture traits are key drivers of this interplay, but our knowledge on rootstock architectures in the field remains limited both qualitatively and quantitatively. We propose phenotyping methods to help close current knowledge gaps and discuss approaches to integrate phenotyping data into different models to advance our understanding of rootstock x environment x management interactions and predict rootstock genotype performance in a changing climate. This could also provide a valuable basis for optimizing breeding efforts to develop new grapevine rootstock cultivars with optimal trait configurations for future growing conditions.

Nitrogen control of transpiration in grapevine

Transpiration per unit of leaf area is the end-product of the root-to-leaf water transport within the plant, and it is regulated by a series of morpho-physiological resistances and hierarchical signals. The rate of water transpired sustains a series of processes such as nutrient absorption and leaf evaporative cooling, with stomata being the end-valves that maintain the optimal water loss under specific degrees of evaporative demand and soil moisture conditions. Previous work provided evidence of a partial modulation of water flux following nitrogen availability linking high nitrate availability with tight stomatal control of transpiration in several species. In this work, we tested the hypothesis that stomatal control of transpiration, among others signals, is partially modulated by soil nitrate ( NO 3 - ) availability in grapevine, with reduced NO 3 - availability (alkaline soil pH, reduced fertilization, and distancing NO 3 - source) associated with decreased water-use efficiency and higher transpiration. We observed a general trend when NO 3 - was limiting with plants increasing either stomatal conductance or root-shoot ratio in four independent experiments with strong associations between leaf water status, stomatal behavior, root aquaporins expression, and xylem sap pH. Carbon and oxygen isotopic signatures confirm the proximal measurements, suggesting the robustness of the signal that persists over weeks and under different gradients of NO 3 - availability and leaf nitrogen content. Nighttime stomatal conductance was unaffected by NO 3 - manipulation treatments, while application of high vapor pressure deficit conditions nullifies the differences between treatments. Genotypic variation for transpiration increase under limited NO 3 - availability was observed between rootstocks indicating that breeding (e.g., for high soil pH tolerance) unintentionally selected for enhanced mass flow nutrient acquisition under restrictive or nutrient-buffered conditions. We provide evidence of a series of specific traits modulated by NO 3 - availability and suggest that NO 3 - fertilization is a potential candidate for optimizing grapevine water-use efficiency and root exploration under the climate-change scenario.

Physiological and Transcriptomic Evaluation of Drought Effect on Own-Rooted and Grafted Grapevine Rootstock (1103P and 101-14MGt)

Grapevines worldwide are grafted onto Vitis spp. rootstocks in order to improve their tolerance to biotic and abiotic stresses. Thus, the response of vines to drought is the result of the interaction between the scion variety and the rootstock genotype. In this work, the responses of genotypes to drought were evaluated on 1103P and 101-14MGt plants, own-rooted and grafted with Cabernet Sauvignon, in three different water deficit conditions (80, 50, and 20% soil water content, SWC). Gas exchange parameters, stem water potential, root and leaf ABA content, and root and leaf transcriptomic response were investigated. Under well-watered conditions, gas exchange and stem water potential were mainly affected by the grafting condition, whereas under sever water deficit they were affected by the rootstock genotype. Under severe stress conditions (20% SWC), 1103P showed an "avoidance" behavior. It reduced stomatal conductance, inhibited photosynthesis, increased ABA content in the roots, and closed the stomata. The 101-14MGt maintained a high photosynthetic rate, limiting the reduction of soil water potential. This behavior results in a "tolerance" strategy. An analysis of the transcriptome showed that most of the differentially expressed genes were detected at 20% SWC, and more significantly in roots than in leaves. A core set of genes has been highlighted on the roots as being related to the root response to drought that are not affected by genotype nor grafting. Genes specifically regulated by grafting and genes specifically regulated by genotype under drought conditions have been identified as well. The 1103P, more than the 101-14MGt, regulated a high number of genes in both own-rooted and grafted conditions. This different regulation revealed that 1103P rootstock readily perceived the water scarcity and rapidly faced the stress, in agreement with its avoidance strategy.

Water deficit before veraison is crucial in regulating berry VOCs concentration in Sangiovese grapevines

The impact of water deficit on volatile organic compounds (VOCs) responsible for grape aroma remains quite unclear. The aim of this study was to evaluate the effect of different timing and intensity of water deficit on berry VOCs and on their biosynthetic pathways. Fully irrigated control vines were compared with the following treatments: i) two different levels of water deficit from berry pea-size through veraison, ii) one level of water deficit during the lag-phase, and iii) two different levels of water deficit from veraison through harvest. At harvest, total VOC concentrations were higher in berries of water stressed vines from berry pea size through veraison or during the lag phase, whereas post-veraison water deficit determined similar concentrations as control. This pattern was even more pronounced for the glycosylated fraction and was also observed for single compounds, mainly monoterpenes and C₁₃-norisoprenoids. On the other hand, free VOCs were higher in berries from lag phase or post-veraison stressed vines. The significant glycosylated and free VOCs increment measured after the short water stress limited to the lag phase highlight the pivotal role played by this stage in berry aroma compound biosynthesis modulation. The severity of water stress before veraison was also important, since glycosylated VOCs showed a positive correlation with the pre-veraison daily water stress integral. The RNA-seq analysis showed a wide regulation induced by irrigation regimes on terpenes and carotenoids biosynthetic pathways. The terpene synthases and glycosyltransferases as well as genes of the network of transcription factors were upregulated, especially in berries from pre-veraison stressed vines. Since the timing and intensity of water deficit contribute to regulate berry VOCs, irrigation management can be used to achieve high-quality grapes while saving water.

Evaluation of the Effect of Deep Compost Application in the Areas around Vineyard Tree Trunks on Selected Soil Chemical Properties and the Vegetative Growth of the Vine

In the context of sustainability, viticulture will address issues related to soil fertility in the coming period. Greater attention will therefore be paid to replacing traditional manure-based fertilisers, such as farmyard manure, with new types of fertiliser in the form of composts, digestate, etc. Experience to date suggests that good-quality composts are not only a source of nutrients that the vines take from the soil each year, but also a source of organic matter. The application of compost and its subsequent decomposition in the soil profile can have a positive effect on the growth of the roots and above-ground parts of the vine. However, optimising the effects and action of compost is linked to determining the necessary doses and methods of application. The aim of this three-year study was to provide an overview of the results aimed at evaluating the effects of the application of compost (CO) and compost enriched with the addition of lignohumate (CO+L20), at a rate of 30 t·ha−1, in the areas around vineyard tree trunks on selected soil chemical properties and the vegetative growth of the vine (Vitis vinifera L.). The unfertilised variant (CWC) was used as a control. Each variant was established in three replicates that were 20 m long. Experimental measurements and evaluation were carried out in the period of 2018–2020 on two sites with different soil conditions (Lednice and Velké Bílovice) and two different grape varieties (Sauvignon Blanc and Pinot Gris). Meteorological data were continuously monitored during the period under review. Chemical properties of the soil samples of the three experimental variants were determined (e.g., content of organic carbon, humic acids, humic substances, humification rate, etc.). The evaluations that were carried out confirmed that the addition of organic matter in the form of composts to the soil in the CO and CO+L20 variants positively influenced the quality of organic matter. The organic carbon content increased by 56–139% in variants with deep compost application (CO, CO+L20) during the monitored period compared to the CWC, depending on the location. Similarly, the degree of humification increased by 70–84%, and the soil microbial biomass increased by 38–136% in the treated variants compared to the CWC. In addition to the dynamics of the changes in the chemical properties, the aim of the performed measurements was to evaluate the rate of the growth shoots, which was linked to the fertilizing effects of the applied compost in the experimental vineyard. At the site in Velké Bílovice, the total difference in the length of the shoots was higher in the CO by 2.6–4.6% and in the CO+L20 by 7.5–12.5% compared to the CWC. At the site in Lednice, the situation was similar, and the total difference in the length of the shoots was higher in the CO by 4.6–7.2% and in the CO+L20 by 5.3–13.2%. The results that were obtained may constitute an important basis for the management of organic fertilization on plots with different soil conditions and cultivated varieties in order to optimize the vegetative growth of the vine.

The Rootstock Genotypes Determine Drought Tolerance by Regulating Aquaporin Expression at the Transcript Level and Phytohormone Balance

Grapevine rootstocks may supply water to the scion according to the transpiration demand, thus modulating plant responses to water deficit, but the scion variety can alter these responses, as well. The rootstock genotypes' effect on the scion physiological response, aquaporin expression, and hormone concentrations in the xylem and the leaf was assessed under well watered (WW) and water stress (WS) conditions. Under WW, vines grafted onto 1103P and R110 rootstocks (the more vigorous and drought-tolerant) showed higher photosynthesis (A_N), stomatal conductance (g_s), and hydraulic conductance (Kh_plant) compared with the less vigorous and drought-sensitive rootstock (161-49C), while under WS, there were hardly any differences between vines depending on the rootstock grafted. Besides, stomatal traits were affected by drought, which was related to g_s, but not by the rootstock. Under WS conditions, all VvPIP and VvTIP aquaporins were up-regulated in the vines grafted onto 1103P and down-regulated in the ones grafted onto 161-49C. The 1103P capability to tolerate drought was enhanced by the up-regulation of all VvPIP and VvTIP aquaporins, lower ABA synthesis, and higher ACC/ABA ratios in leaves during WS compared with 161-49C. It was concluded that, under WW conditions, transpiration and stomatal control were rootstock-dependent. However, under WS conditions, alterations in the molecular components of water transport and hormone concentration of the scion resulted in similar gas exchange values in the studied scions grafted onto different rootstocks.

Global transcriptome and gene co-expression network analyses reveal regulatory and non-additive effects of drought and heat stress in grapevine

Despite frequent co-occurrence of drought and heat stress, the molecular mechanisms governing plant responses to these stresses in combination have not often been studied. This is particularly evident in non-model, perennial plants. We conducted large scale physiological and transcriptome analyses to identify genes and pathways associated with grapevine response to drought and/or heat stress during stress progression and recovery. We identified gene clusters with expression correlated to leaf temperature and water stress and five hub genes for the combined stress co-expression network. Several differentially expressed genes were common to the individual and combined stresses, but the majority were unique to the individual or combined stress treatments. These included heat-shock proteins, mitogen-activated kinases, sugar metabolizing enzymes, and transcription factors, while phenylpropanoid biosynthesis and histone modifying genes were unique to the combined stress treatment. Following physiological recovery, differentially expressed genes were found only in plants under heat stress, both alone and combined with drought. Taken collectively, our results suggest that the effect of the combined stress on physiology and gene expression is more severe than that of individual stresses, but not simply additive, and that epigenetic chromatin modifications may play an important role in grapevine responses to combined drought and heat stress.

Effect of drought on aquaporin expression in grafted and ungrafted grapevine cultivars

Drought stress severely affects growth, development and productivity in most agricultural crops. Since ancient times, rootstocks have been used to enable crop cultivation in unsuitable soil conditions. In the present study, three factors were evaluated: 1) cultivar: Vitis vinifera L. cv. ‘Horozkarası’ (drought-tolerant) and cv. ‘Kabarcık’ (drought-sensitive) were used; 2) rootstock: each cultivar was self-rooted and grafted onto ‘Rupestris du Lot’ rootstock; 3) drought stress: half of each cultivar/rootstock combination underwent drought stress and the other half was irrigated at field capacity for seven days. In order to estimate the responses of the cultivars, relative water content, proline content and aquaporin isoform expression levels (VvPIP2;1, VvPIP2;2, VvTIP1;1, and VvTIP2;1) were quantified. The results revealed that drought stress caused more reduction in relative water content (RWC) in ‘Kabarcık’ cultivar (drought-sensitive) than in ‘Horozkarası’ cultivar (drought-tolerant). Proline content increased in both cultivars in response to drought stress but to a relatively greater extent in the grafted ‘Kabarcık’ cultivar. Considering expression levels of genes, VvPIP2;1, VvPIP2;2, and VvTIP2;1 were downregulated whilst VvTIP1;1 was upregulated in the leaf. Both ‘Horozkarası’ and ‘Kabarcık’ cultivars showed similar trends in terms of their responses to drought stress. Grafting significantly increased the proline content in both cultivars exposed to drought stress. The rootstock conferred better drought protection to ‘Kabarcık’ cultivar than to ‘Horozkarası’ cultivar.

Grape Berry Responses to Sequential Flooding and Heatwave Events: A Physiological, Transcriptional, and Metabolic Overview

Grapevine cultivation, such as the whole horticulture, is currently challenged by several factors, among which the extreme weather events occurring under the climate change scenario are the most relevant. Within this context, the present study aims at characterizing at the berry level the physiological response of Vitis vinifera cv. Sauvignon Blanc to sequential stresses simulated under a semi-controlled environment: flooding at bud-break followed by multiple summer stress (drought plus heatwave) occurring at pre-vèraison. Transcriptomic and metabolomic assessments were performed through RNASeq and NMR, respectively. A comprehensive hormone profiling was also carried out. Results pointed out a different response to the heatwave in the two situations. Flooding caused a developmental advance, determining a different physiological background in the berry, thus affecting its response to the summer stress at both transcriptional levels, with the upregulation of genes involved in oxidative stress responses, and metabolic level, with the increase in osmoprotectants, such as proline and other amino acids. In conclusion, sequential stress, including a flooding event at bud-break followed by a summer heatwave, may impact phenological development and berry ripening, with possible consequences on berry and wine quality. A berry physiological model is presented that may support the development of sustainable vineyard management solutions to improve the water use efficiency and adaptation capacity of actual viticultural systems to future scenarios.

PIN1 regulates epidermal cells development under drought and salt stress using single-cell analysis

Over the course of evolution, plants have developed plasticity to acclimate to environmental stresses such as drought and salt stress. These plant adaptation measures involve the activation of cascades of molecular networks involved in stress perception, signal transduction and the expression of stress related genes. Here, we investigated the role of the plasma membrane-localized transporter of auxin PINFORMED1 (PIN1) in the regulation of pavement cells (PCs) and guard cells (GCs) development under drought and salt stress conditions. The results showed that drought and salt stress treatment affected the development of PCs and GCs. Further analysis identified the different regulation mechanisms of PIN1 in regulating the developmental patterns of PCs and GCs under drought and salt stress conditions. Drought and salt stress also regulated the expression dynamics of PIN1 in pif1/3/4/5 quadruple mutants. Collectively, we revealed that PIN1 plays a crucial role in regulating plant epidermal cells development under drought and salt stress conditions, thus contributing to developmental rebustness and plasticity.

Unraveling the Physiological Mechanisms Underlying the Intracultivar Variability of Water Use Efficiency in Vitis vinifera "Grenache"

Selecting genotypes with a better capacity to respond and adapt to soil water deficits is essential to achieve the sustainability of grapevine cultivation in the context of increasing water scarcity. However, cultivar changes are very poorly accepted, and therefore it is particularly interesting to explore the intracultivar genetic diversity in water use efficiency (WUE). In previous studies, the cultivar "Grenache" has shown up to 30% variability in WUE. This research aimed to confirm the intracultivar variability and to elucidate the traits underlying this variability in the response to a water deficit by analyzing the growth rates, water relations, osmotic potential, leaf morphology, leaf gas exchange and carbon isotope discrimination in nine "Grenache" genotypes grown in pots during two seasons. The results showed lower differences in WUE and carbon isotope ratio than in previous field studies, but fairly good consistency in genotype ranking. Leaf mass area and osmotic potential did not underlie differences in stem water potential and in stomatal conductance. Overall, stomatal regulation and photosynthetic capacity seem to underlie differences in WUE among genotypes with an important environmental influence. These results confirm the ability to select clones with higher WUE and present an opportunity for the genetic improvement of WUE in grapevines.

Photosynthetic recovery in drought-rehydrated grapevines is associated with high demand from the sinks, maximizing the fruit-oriented performance

To understand how grapevine sinks compete with each other during water stress and subsequent rehydration, carbon (C) allocation patterns in drought-rehydrated vines (REC) at the beginning of fruit ripening were compared with control vines maintained under drought (WS) or fully irrigated (WW). In the 30 days following rehydration, the quantity and distribution of newly fixed C between leaves, roots and fruits was evaluated through ¹³ CO₂ pulse-labeling and stable isotope ratio mass spectrometry. REC plants diverted the same percentage of fixed C towards the berries as the WS plants, although the percentage was higher than that of WW plants. Net photosynthesis (measured simultaneously with root respiration in a multichamber system for analysis of gas exchange above- and below-ground) was approximately two-fold greater in REC compared to WS treatment, and comparable or even higher than in WW plants. Maximizing C assimilation and delivery in REC plants led to a significantly higher amount of newly fixed C compared to both control treatments, already 2 days after rehydration in root, and 2 days later in the berries, in line with the expression of genes responsible for sugar metabolism. In REC plants, the increase in C assimilation was able to support the requests of the sinks during fruit ripening, without affecting the reserves, as was the case in WS. These mechanisms clarify what is experienced in fruit crops, when occasional rain or irrigation events are more effective in determining sugar delivery towards fruits, rather than constant and satisfactory water availabilities.

Berry flavonoids are differently modulated by timing and intensities of water deficit in Vitis vinifera L. cv. Sangiovese

In this work, we tested the effect of different regulated deficit irrigation (RDI) regimes on berry flavonoid content and its relative biosynthetic pathways. Vines were subjected to six irrigation regimes over two consecutive years: a) full irrigation during the entire irrigation period (FI); b) moderate (RDI-1M) or c) severe (RDI-1S) water deficit between berry pea-size and veraison; d) severe water deficit during the lag-phase (RDI-LS); and e) moderate (RDI-2M) or f) severe (RDI-2S) water deficit from veraison through harvest. Berries from both RDI-1 treatments showed the highest accumulation of anthocyanins, upregulating the expression of many genes of the flavonoid pathway since the beginning of veraison until harvest, far after the water deficit was released. Although to a lesser degree than RDI-1, both post-veraison water deficit treatments increased anthocyanin concentration, particularly those of the tri-substituted forms, overexpressing the F3'5'H hydroxylases. The moderate deficit irrigation treatments enhanced anthocyanin accumulation with respect to the severe ones regardless of the period when they were applied (pre- or post-veraison). The water deficit imposed during the lag-phase downregulated many genes throughout the flavonoid pathway, showing a slight reduction in anthocyanin accumulation. The measurements of cluster temperature and light exposure highlighted that under deficit irrigation conditions, the effects induced by water stress prevailed over that of light and temperature in regulating anthocyanin biosynthesis. Flavonol concentration was higher in RDI-1S berries due to the upregulation of the flavonol synthases and the flavonol-3-O-glycosyltransferases. In this case, the higher cluster light exposure induced by water deficit in RDI-1S berries had a major role in flavonol accumulation. We conclude that the timing and intensity of water stress strongly regulate the berry flavonoid accumulation and that proper management of deficit irrigation can modulate the phenylpropanoid and flavonoid pathways.

Prospecting the Resilience of Several Spanish Ancient Varieties of Red Grape under Climate Change Scenarios

BACKGROUND

Climate change results in warmer air temperatures and an uncertain amount and distribution of annual precipitations, which will directly impact rainfed crops, such as the grapevine. Traditionally, ancient autochthones grapevine varieties have been substituted by modern ones with higher productivity. However, this homogenization of genotypes reduces the genetic diversity of vineyards which could make their ability to adapt to challenges imposed by future climate conditions difficult. Therefore, this work aimed to assess the response of four ancient grapevine varieties to high temperatures under different water availabilities, focusing on plant water relations, grape technological and phenolic maturity, and the antioxidant capacity of the must.

METHODS

The study was conducted on fruit-bearing cuttings grown in pots in temperature-gradient greenhouses. A two-factorial design was established where two temperature regimes, ambient and elevated (ambient + 4 °C), were combined with two water regimes, full irrigation and post-veraison deficit irrigation, during fruit ripening.

RESULTS

There were significant differences among the ancient varieties regarding plant water relations and fruit quality.

CONCLUSION

This research underlines the importance of evaluating the behavior of ancient grapevine varieties that could offer good options for the adaptation of viticulture to future climate conditions.

Model-assisted ideotyping reveals trait syndromes to adapt viticulture to a drier climate

Climate change is challenging the resilience of grapevine (Vitis), one of the most important crops worldwide. Adapting viticulture to a hotter and drier future will require a multifaceted approach including the breeding of more drought-tolerant genotypes. In this study, we focused on plant hydraulics as a multi-trait system that allows the plant to maintain hydraulic integrity and gas exchange rates longer under drought. We quantified a broad range of drought-related traits within and across Vitis species, created in silico libraries of trait combinations, and then identified drought tolerant trait syndromes. By modeling the maintenance of hydraulic integrity of current cultivars and the drought tolerant trait syndromes, we identified elite ideotypes that increased the amount of time they could experience drought without leaf hydraulic failure. Generally, elites exhibited a trait syndrome with lower stomatal conductance, earlier stomatal closure, and a larger hydraulic safety margin. We demonstrated that, when compared with current cultivars, elite ideotypes have the potential to decrease the risk of hydraulic failure across wine regions under future climate scenarios. This study reveals the syndrome of traits that can be leveraged to protect grapevine from experiencing hydraulic failure under drought and increase drought tolerance.

Effect of three water-regimes on morpho-physiological, biochemical and yield responses of local and foreign olive cultivars under field conditions

BACKGROUND

Drought stress is among the most serious threats jeopardizing the economic yield of crop plants in Iran. In particular, in response to withholding irrigation, the reduction in performance and quality of a precious plant such as the olive tree is remarkable. Therefore, the selection of cultivars that are resistant or tolerant to drought has been recognized as one of the most effective long-term strategies for sustainably alleviating the adverse effects of this stress. In this view, our study evaluated the response of 8 olive cultivars including 4 elite native cultivars (Zard Aliabad, Roughani, Dezful, and Shengeh) and 4 foreign cultivars (Manzanilla, Sevillana, Konservolia, and Mission) to water shortage in the Dallaho Olive Research station of Sarpole-Zahab in Kermanshah province in 2020. Olive trees underwent 3 levels of irrigation treatment including 100% full irrigation (control), 75%, and 50% deficit irrigation.

RESULTS

Based on the results, 50% deficit irrigation decreased both growth and pomological traits, but determined the highest dry matter percentage. As the severity of drought stress increased, with an accumulation of sodium and malondialdehyde, an incremental increase in osmolytes was observed, as well as an enhancement of the activity of antioxidant enzymes (peroxidase and catalase). In contrast, full irrigation led to an increase in photosynthetic pigments, calcium, and potassium. Dezful and Konservolia cultivars revealed a significantly higher growth rate, correlated in the former to higher levels of chlorophyll, compatible compounds, total phenolic content, relative water content, potassium to sodium ratio, catalase, and peroxidase activities compared with other cultivars. Konservolia showed the best yield parameters under 75% and 100% irrigation regimes, correlated to higher chlorophyll, potassium, and total phenolic content (in particular at 75% ET).

CONCLUSIONS

Generally, the selection of more resilient or tolerant cultivars to sustain water scarcity stress is a widely operative solution to extend rainfed orchards in semi-arid environments. Our study showed that Dezful and Konservolia had the best adaptive mechanisms to cope with the detrimental effects of drought stress.

A Field Collection of Indigenous Grapevines as a Valuable Repository for Applied Research

The grapevine is an economically important plant, with a historical connection to the development of human culture. Currently, over 6000 accessions are known as individual grapevine varieties, some of which are important to national heritage, valuable for current viticultural practices, and as genetic resources to maintain plasticity under changing climatic conditions, environmental sustainability, and market demands. Recently, the diversity of cultivated grapevines has declined significantly, due to the increased focus of global wine industries on a few major cultivars. Moreover, due to biotic and abiotic stresses, the wild V. vinifera germplasm's genetic diversity has declined, with some varieties on the verge of extinction. Vitis germplasm conservation can be achieved via either in situ (e.g., protected areas) or Ex situ (e.g., field collections, seed banks, and tissue culture collections) methods. This study aims to highlight the importance of Vitis field bank collections. We demonstrate the research done in the Israeli indigenous Vitis vinifera collection. The multi-layer analysis of the varieties enabled the identification of drought stress-resistant varieties, and suggested a mechanism for this resistance through noting the dramatic phenological differences in foliage development between resistant and sensitive varieties. In addition, we show a general characterization of the varieties via major grape characteristics, including bunch and berry shape, as well as their possible utilization based on their aromatic and phenolic profiles.

Examining physiological, water relations, and hydraulic vulnerability traits to determine anisohydric and isohydric behavior in almond (Prunus dulcis) cultivars: Implications for selecting agronomic cultivars under changing climate

The search for drought tolerant species or cultivars is important to address water scarcity caused by climate change in Mediterranean regions. The anisohydric-isohydric behavior concept has been widely used to describe stomatal regulation during drought, simply in terms of variation of minimal water potential (Ψ_min) in relation to pre-dawn water potential (Ψ_pd). However, its simplicity has sometimes failed to deliver consistent results in describing a complex behavior that results from the coordination of several plant functional traits. While Prunus dulcis (almond) is known as a drought tolerant species, little information is available regarding consistent metrics to discriminate among cultivars or the mechanisms underlying drought tolerance in almond. Here we show a sequence of plant stomatal, hydraulic, and wilting responses to drought in almonds, and the main differences between anisohydric and isohydric cultivars. In a pot desiccation experiment we observed that stomatal closure in P. dulcis is not driven by loss in turgor or onset of xylem cavitation, but instead, occurs early in response to decreasing Ψ_min that could be related to the protection of the integrity of the hydraulic system, independently of cultivar. Also, we report that anisohydric cultivars of P. dulcis are characterized by maximum stomatal conductance, lower water potentials for stomatal closure and turgor loss, and lower vulnerability to xylem cavitation, which are traits that correlated with metrics to discriminate anisohydric and isohydric behavior. Our results demonstrate that P. dulcis presents a strategy to avoid cavitation by closing stomata during the early stages of drought. Future research should also focus on below-ground hydraulic traits, which could trigger stomatal closure in almond.

A Comprehensive Evaluation of Effects on Water-Level Deficits on Tomato Polyphenol Composition, Nutritional Quality and Antioxidant Capacity

Tomatoes have high nutritional value and abundant bioactive compounds. Moderate water deficit irrigation alters metabolic levels of fruits, improving composition and quality. We investigated the effects of water deficit (T1, T2, T3, and T4) treatments and adequate irrigation (CK) on tomato polyphenol composition, antioxidant capacity, and nutritional quality. Compared with CK, the total flavonoid content increased by 33.66% and 44.73% in T1 and T2, and total phenols increased by 57.64%, 72.22%, and 55.78% in T1, T2, and T3, respectively. The T2 treatment significantly enhanced antioxidant’ capacities (ABTS, HSRA, FRAP, and DPPH). There were multiple groups of significant or extremely significant positive correlations between polyphenol components and antioxidant activity. For polyphenols and antioxidant capacity, the classification models divided the treatments: CK and T4 and T1−T3. The contents of soluble solids, soluble protein, vitamin C, and soluble sugar of the treatment groups were higher than those of CK. The soluble sugar positively correlated with sugar−acid ratios. In the PCA-based model, T3 in the first quadrant indicated the best treatment in terms of nutritional quality. Overall, comprehensive rankings using principal component analysis (PCA) revealed T2 > T1 > T3 > T4 > CK. Therefore, the T2 treatment is a suitable for improving quality and antioxidant capacity. This study provides novel insights into improving water-use efficiency and quality in the context of water scarcity worldwide.

Water Deficit Timing Differentially Affects Physiological Responses of Grapevines Infected with Lasiodiplodia theobromae

Diseases and climate change are major factors limiting grape productivity and fruit marketability. Lasiodiplodia theobromae is a fungus of the family Botryosphaeriaceae that causes Botryosphaeria dieback of grapevine worldwide. Abiotic stress may change host vitality and impact susceptibility to the pathogen and/or change the pathogen's life cycle. However, the interaction between both stress drivers is poorly understood for woody plants. We addressed the hypothesis that distinct morpho-physiological and biochemical responses are induced in grapevine (Vitis vinifera)-L. theobromae interactions depending on when water deficits are imposed. Grapevines were submitted to water deficit either before or after fungus inoculation. Water deficit led to the reduction of the net photosynthetic rate, stomatal conductance, and transpiration rate, and increased the abscisic acid concentration regardless of fungal inoculation. L. theobromae inoculation before water deficit reduced plant survival by 50% and resulted in the accumulation of jasmonic acid and reductions in malondialdehyde levels. Conversely, grapevines inoculated after water deficit showed an increase in proline and malondialdehyde content and all plants survived. Overall, grapevines responded differently to the primary stress encountered, with consequences in their physiological responses. This study reinforces the importance of exploring the complex water deficit timing × disease interaction and the underlying physiological responses involved in grapevine performance.

The AP2/ERF GmERF113 Positively Regulates the Drought Response by Activating GmPR10-1 in Soybean

Ethylene response factors (ERFs) are involved in biotic and abiotic stress; however, the drought resistance mechanisms of many ERFs in soybeans have not been resolved. Previously, we proved that GmERF113 enhances resistance to the pathogen Phytophthora sojae in soybean. Here, we determined that GmERF113 is induced by 20% PEG-6000. Compared to the wild-type plants, soybean plants overexpressing GmERF113 (GmERF113-OE) displayed increased drought tolerance which was characterized by milder leaf wilting, less water loss from detached leaves, smaller stomatal aperture, lower Malondialdehyde (MDA) content, increased proline accumulation, and higher Superoxide dismutase (SOD) and Peroxidase (POD) activities under drought stress, whereas plants with GmERF113 silenced through RNA interference were the opposite. Chromatin immunoprecipitation and dual effector-reporter assays showed that GmERF113 binds to the GCC-box in the GmPR10-1 promoter, activating GmPR10-1 expression directly. Overexpressing GmPR10-1 improved drought resistance in the composite soybean plants with transgenic hairy roots. RNA-seq analysis revealed that GmERF113 downregulates abscisic acid 8′-hydroxylase 3 (GmABA8’-OH 3) and upregulates various drought-related genes. Overexpressing GmERF113 and GmPR10-1 increased the abscisic acid (ABA) content and reduced the expression of GmABA8’-OH3 in transgenic soybean plants and hairy roots, respectively. These results reveal that the GmERF113-GmPR10-1 pathway improves drought resistance and affects the ABA content in soybean, providing a theoretical basis for the molecular breeding of drought-tolerant soybean.