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Rootstocks are potentially important levers of adaptation in the context of climate change. In this study, we investigated the effect of the rootstock and its genetic background on plant mineral status. The scion, the rootstock, and their interactions had a significant influence on petiole mineral content and explained the same proportion of phenotypic variance for most mineral elements. The rootstock effect was higher than the scion effect on the petiole concentration of a large majority of mineral elements. The joint evaluation of mineral status and deficiency symptoms highlights the diversity of rootstock-induced responses, and thus a new rootstock classification can be proposed to help growers optimise plant nutrition and fertiliser management.

The past decade has produced some major advances in our understanding of how grapevines regulate their water use and tolerate drought. Numerous traits that are important for conferring drought tolerance have been identified and quantified across a range of cultivars (Dayer et al., 2022). Nevertheless, arriving at a firm hierarchical rating of different cultivars’ drought tolerance has eluded scientists. This short review seeks to explain how drought tolerance is dependent on multiple traits, all interacting within a particular environment and management context.

Abstract Background Soil microorganisms play an extensive role in the biogeochemical cycles providing the nutrients necessary for plant growth. Root-associated bacteria and fungi, originated from soil, are also known to influence host health. In response to environmental stresses, the plant roots exude specific molecules influencing the composition and functioning of the rhizospheric and root microbiomes. This response is host genotype-dependent and is affected by the soil microbiological and chemical properties. It is essential to unravel the influence of grapevine rootstock and scion genotypes on the composition of this microbiome, and to investigate this relationship with plant growth and adaptation to its environment. Here, the composition and the predicted functions of the microbiome of the root system were studied using metabarcoding on ten grapevine scion-rootstock combinations, in addition to plant growth and nutrition measurements. Results The rootstock genotype significantly influenced the diversity and the structure of the bacterial and fungal microbiome, as well as its predicted functioning in rhizosphere and root compartments when grafted with the same scion cultivar. Based on β-diversity analyses, 1103P rootstock showed distinct bacterial and fungal communities compared to the five others (RGM, SO4, 41B, 3309 C and Nemadex). The influence of the scion genotype was more variable depending on the community and the investigated compartment. Its contribution was primarily observed on the β-diversity measured for bacteria and fungi in both root system compartments, as well as for the arbuscular mycorrhizal fungi (AMF) in the rhizosphere. Significant correlations were established between microbial variables and the plant phenotype, as well as with the plant mineral status measured in the petioles and the roots. Conclusion These results shed light on the capacity of grapevine rootstock and scion genotypes to recruit different functional communities of microorganisms, which affect host growth and adaptation to the environment. Selecting rootstocks capable of associating with positive symbiotic microorganisms is an adaptation tool that can facilitate the move towards sustainable viticulture and help cope with environmental constraints.

When grapevine decline, characterized by a premature decrease in vigor and yield and sometimes plant death, cannot be explained by pathological or physiological diseases, one may inquire whether the microbiological status of the soil is responsible. Previous studies have shown that the composition and structure of bacterial and fungal microbial communities in inter-row soil are affected in areas displaying vine decline, compared to areas with non-declining vines within the same plot. A more comprehensive analysis was conducted in one such plot. Although soil chemical parameters could not directly explain these differences, the declining vines presented lower vigor, yield, berry quality, and petiole mineral content than those in non-declining vines. The bacterial and fungal microbiome of the root endosphere, rhizosphere, and different horizons of the bulk soil were explored through enzymatic, metabolic diversity, and metabarcoding analysis in both areas. Despite the lower microbial diversity and richness in symptomatic roots and soil, higher microbial activity and enrichment of potentially both beneficial bacteria and pathogenic fungi were found in the declining area. Path modeling analysis linked the root microbial activity to berry quality, suggesting a determinant role of root microbiome in the berry mineral content. Furthermore, certain fungal and bacterial taxa were correlated with predicted metabolic pathways and metabolic processes assessed with Eco-Plates. These results unexpectedly revealed active microbial profiles in the belowground compartments associated with stressed vines, highlighting the interest of exploring the functional microbiota of plants, and more specifically roots and rhizosphere, under stressed conditions.

Rootstocks are an important means of adapting grapevine to environmental conditions whilst conserving the typical features of scion genotypes. Rootstocks not only provide tolerance to Phylloxera, but also ensure the supply of water and mineral nutrients to the scion. We take advantage of the large diversity of rootstocks used worldwide to facilitate this adaptation. The aim of this study was to characterise rootstock regulation of scion mineral status and its relationship with scion development. Vitis vinifera cvs. Cabernet-Sauvignon, Pinot noir, Syrah and Ugni blanc were grafted onto 55 different rootstock genotypes and planted as three replicates of five plants in sandy gravelly soil near Bordeaux, France. In 2020 and 2021, petiolar concentrations of 13 mineral elements (N, P, K, S, Mg, Ca, Na, B, Zn, Mn, Fe, Cu and Al) were measured at veraison. Winter pruning weight, shoot vigour, leaf chlorophyll content, bud fertility and yield were measured. Magnesium deficiency severity was visually scored for each plant. Rootstocks were grouped according to their Vitis parentage background when at least 50 % of a Vitis species was present in order to determine whether the petiole mineral composition could be related to the rootstock genetic parentage. Scion, rootstock, and their interactions had a significant influence on petiole mineral content and explained the same proportion of phenotypic variance for most mineral elements. Rootstock effect explained 9, 28 and 45 % of the mineral content variance for N, Mg and S respectively. This unique experimental design showed that the rootstock effect was higher than the scion effect on the petiole concentration of a large majority of mineral elements. The genetic background V. riparia increased the probability of low petiolar P and Mg contents. The severity of Mg deficiency symptoms varied depending on the rootstock. The differences in mineral status conferred by rootstocks were not significantly correlated with vigour or fertility. The evaluation of Mg levels by petiole analysis and the intensity of deficiency symptoms showed for the first time the variability of the thresholds of satisfactory mineral nutrition between rootstocks. Therefore, fertiliser management should take the rootstock variety into account.

Abstract In grafted plants, such as grapevine, increasing the diversity of rootstocks available to growers is an ideal strategy for helping plants to adapt to climate change. The rootstocks used for grapevine are hybrids of various American Vitis, including V. berlandieri. The rootstocks currently use in vineyards are derived from breeding programs involving very small numbers of parental individuals. We investigated the structure of a natural population of V. berlandieri and the association of genetic diversity with environmental variables. In this study, we collected seeds from 78 wild V. berlandieri plants in Texas after open fertilization. We genotyped 286 individuals to describe the structure of the population, and environmental information collected at the sampling site made it possible to perform genome–environment association analysis (GEA). De novo long‐read whole‐genome sequencing was performed on V. berlandieri and a STRUCTURE analysis was performed. We identified and filtered 104,378 SNPs. We found that there were two subpopulations associated with differences in elevation, temperature, and rainfall between sampling sites. GEA identified three QTL for elevation and 15 QTL for PCA coordinates based on environmental parameter variability. This original study is the first GEA study to be performed on a population of grapevines sampled in natural conditions. Our results shed new light on rootstock genetics and could open up possibilities for introducing greater diversity into genetic improvement programs for grapevine rootstocks.

French research on rootstocks is based on two strategies: the creation of new rootstocks and the evaluation of existing rootstocks (GreffAdapt facility). The search for traits associated with drought tolerance has not yet been brought to a successful conclusion, but work is continuing with the emphasis on field experiments, measurement of δ13C, consideration of yield, and study of trait plasticity as a function of the scion and the water status.

To sustain local wine identity in uncertain climate outcomes, the study of intra-varietal diversity is important to reflect the adaptive potential of cultivated varieties. Findings highlight the strong phenotypic diversity of studied varieties and the importance of diversification to enhance climate change resilience. This study is the first step towards quantifying heat requirements of different clones and how they can provide adaptation solutions for winegrowers.

Soil microbiota plays a significant role in plant development and health and appears to be a major component of certain forms of grapevine decline. A greenhouse experiment was conducted to study the impact of the microbiological quality of the soil and grapevine rootstock genotype on the root microbial community and development of young plants. Two rootstocks heterografted with the same scion were grown in two vineyard soils differing in microbial composition and activities. After 4 months, culture-dependent approaches and amplicon sequencing of bacterial 16S rRNA gene and fungal ITS were performed on roots, rhizosphere and bulk soil samples. The root mycorrhizal colonization and number of cultivable microorganisms in the rhizosphere compartment of both genotypes were clearly influenced by the soil status. The fungal diversity and richness were dependent on the soil status and the rootstock, whereas bacterial richness was affected by the genotype only. Fungal genera associated with grapevine diseases were more abundant in declining soil and related root samples. The rootstock affected the compartmentalization of microbial communities, underscoring its influence on microorganism selection. Fluorescence in situ hybridization (FISH) confirmed the presence of predominant root-associated bacteria. These results emphasized the importance of rootstock genotype and soil composition in shaping the microbiome of young vines.

In wine growing regions around the world, climate change has the potential to affect vine transpiration and overall vineyard water use due to related changes in daily atmospheric conditions and soil water deficits. Grapevines control their transpiration in response to such changes by regulating conductance of water through the soil-plant-atmosphere continuum. The response of bulk stomatal conductance, the vine canopy equivalent of stomatal conductance, to such changes were studied on Cabernet-Sauvignon, Merlot, Tempranillo, Ugni blanc, and Semillon vines in a non-irrigated vineyard in Bordeaux France. Whole-vine sap flow, temperature and humidity in the vine canopy, and net radiation absorbed by the vine canopy were measured on 15-minute intervals from early July through mid-September 2020, together with periodic measurements of leaf area, canopy porosity, and predawn leaf water potential. From these data, bulk stomatal conductance was calculated on 15-minute intervals, and multiple linear regression analysis was performed to identify key variables and their relative effect on conductance. For the regression analysis, attention was focused on addressing non-linearity and collinearity in the explanatory variables and developing a model that was readily interpretable. Variability of vapour pressure deficit in the vine canopy over the day and predawn water potential over the season explained much of the variability in bulk stomatal conductance overall, with relative differences between varieties appearing to be driven in large part by differences in conductance response to predawn water potential between the varieties. Transpiration simulations based on the regression equations found similar differences between varieties in terms of daily and seasonal transpiration. These simulations also compared well with those from an accepted vineyard water balance model, although there appeared to be differences between the two approaches in the rate at which conductance, and hence transpiration is reduced as a function of decreasing soil water content (i.e., increasing water deficit stress). By better characterizing the response of bulk stomatal conductance, the dynamics of vine transpiration can be better parameterized in vineyard water use modeling of current and future climate scenarios.

Measurement of carbon isotope discrimination in berry juice at maturity (δ13C) provides an integrated assessment of vine water status and water use efficiency (WUE) during the period of berry ripening, and when collected over multiple seasons, can provide an indication of drought stress responses. Berry juice δ13C measurements were carried out on 48 different varieties planted in a common garden experiment in Bordeaux, France from 2014 through 2020 and found important differences across this large panel of varieties. Cluster analysis showed that δ13C values are likely affected by the differing phenology of each variety, resulting in berry ripening of different varieties taking place under different conditions of soil water availability within the same year. Accounting for these phenological differences, the cluster analysis created a classification of varieties that corresponds well to our current empirical understanding of their relative drought tolerance. In addition, using measurements of predawn and midday leaf water potential measurements collected over four seasons on a subset of six varieties, a hydroscape approach was used to develop a list of metrics indicative of the sensitivity of stomatal regulation to water stress (i.e., an/isohydric behaviour). Key hydroscape metrics were also found to be well correlated with some δ13C metrics. A variety’s water potential regulation as characterized by a minimum critical leaf water potential as determined from hydroscapes was strongly correlated to δ13C values under well-watered conditions, suggesting that the latter may be a useful indicator of drought stress response.

In response to changes in their environments, grapevines regulate transpiration using various physiological mechanisms that alter conductance of water through the soil-plant-atmosphere continuum. Expressed as bulk stomatal conductance at the canopy scale, it varies diurnally in response to changes in vapor pressure deficit and net radiation, and over the season to changes in soil water deficits and hydraulic conductivity of both the soil and plant. To help with future characterization of this dynamic response, a simplified method is presented for determining bulk stomatal conductance based on the crop canopy energy flux model by Shuttleworth and Wallace using measurements of individual vine sap flow, temperature and humidity within the vine canopy, and estimates of net radiation absorbed by the vine canopy. The methodology presented respects the energy flux dynamics of vineyards with open canopies, while avoiding problematic measurements of soil heat flux and boundary layer conductance needed by other methods, which might otherwise interfere with ongoing vineyard management practices. Based on this method and measurements taken on several vines in a non-irrigated vineyard in Bordeaux France, bulk stomatal conductance was estimated on 15-minute intervals from July to mid-September 2020 producing values similar to those presented for vineyards in the literature. Time-series plots of this conductance show significant diurnal variation and seasonal decreases in conductance associated with increased vine water stress as measured by predawn leaf water potential. Global sensitivity analysis using non-parametric regression found transpiration flux and vapor pressure deficit to be the most important input variables to the calculation of bulk stomatal conductance, with absorbed net radiation and bulk boundary layer conductance being much less important. Conversely, bulk stomatal conductance was one of the most important inputs when calculating vine transpiration, emphasizing the usefulness of characterizing its dynamic response for the purpose of estimating vine canopy transpiration in water use models.

Grapevine decline is a top concern in viticulture worldwide and is often associated with many biotic and abiotic factors. Grape trunk diseases and viruses are some of the most frequently identified causes of vine dieback. However, a decline is sometimes observed when no mineral deficiency or excess, or pathogenic causes can be identified. Soil enzymatic and microbial activities are relevant bio-indicators since they are known to influence vine health. Grapevine associated microbiota, linked to vine fitness, is known to be influenced by soil microbiota coming from the microbial pool inhabiting the vineyard. This work describes the microbial diversity and activity of four different vineyard plots of the Bordeaux region, selected due to the presence of localised declining areas unexplained yet by disease symptoms. Soils were sampled in declining areas and areas within the same plot showing no decline symptoms, during autumn and spring periods. Significant differences in enzymatic activities, microbial biomass and activity were found among soils even if those soils presented quite similar physicochemical characteristics that could not explain these observed declines. The results of enzymatic assays distinguished patterns in autumn and spring periods with an overall greater enzymatic activity in soils from non-declining areas. This work suggests that soils displaying decline symptoms present a dysbiosis in functionality and diversity which is linked to vine health.

Designing genotypes with acceptable performance under warmer or drier environments is essential for sustainable crop production in view of climate change. However, this objective is not trivial for grapevine since traits targeted for genetic improvement are complex and result from many interactions and trade-off between various physiological and molecular processes that are controlled by many environmental conditions. Integrative tools can help to understand and unravel these Genotype × Environment interactions. Indeed, models integrating physiological processes and their genetic control have been shown to provide a relevant framework for analyzing genetic diversity of complex traits and enhancing progress in plant breeding for various environments. Here we provide an overview of the work conducted by the French LACCAVE research consortium on this topic. Modeling abiotic stress tolerance and fruit quality in grapevine is a challenging issue, but it will provide the first step to design and test in silico plants better adapted to future issues of viticulture.

Backgrounds and aims: Grapevine, Vitis vinifera, requires grafting on Phylloxera tolerant rootstocks of American origin in most viticultural areas of the world. The most commonly used species in rootstock creation are V. berlandieri, V. riparia and V. rupestris. Rootstocks not only provide tolerance to Phylloxera but assure the supply of water and mineral nutrients to the scion. The objective of this work was to determine to what extent rootstocks of different genetic backgrounds alter the mineral composition of petioles of grapevine. Methods and results: Vitis vinifera cv. Cabernet Sauvignon was grafted onto 13 rootstock genotypes and planted in a vineyard in three blocks. The concentration of 13 mineral elements was determined in the petioles at veraison (berry softening). Genetic background of rootstocks has a significant effect on petiole mineral composition. Rootstocks with at least one V. riparia genetic background reduced the concentration of phosphorus and magnesium and increased the concentration of sulphur in the petiole of Cabernet Sauvignon. Conclusion: Rootstocks with a V. riparia genetic background generally confer low scion vigour and we have shown that they also confer low petiole phosphorus concentration; this could suggest that phosphorus uptake and use is related to known rootstock conferred vigour in grapevine. Significance of the study: This is the first study to demonstrate a significant link between the genetic background of a rootstock genotype and its ability to regulate scion phosphorus, magnesium and sulphur content, in field conditions.

Background and aims: In most viticultural areas of the world, Vitis vinifera grapevines require grafting onto phylloxera-tolerant rootstocks of American origin. The species most commonly used in rootstock creation are Vitis berlandieri, V. riparia and V. rupestris. Rootstocks not only provide tolerance to phylloxera but also ensure the supply of water and mineral nutrients to the scion. The aim of the study was to investigate the extent to which rootstocks with different genetic backgrounds modify the mineral composition of the petioles of the scion. Methods and results: Vitis vinifera cv. Cabernet-Sauvignon grapevines were grafted onto rootstocks of 13 different genotypes and planted in a vineyard in three blocks. Petiolar concentrations of 13 mineral elements at veraison (berry softening) were determined. The genetic background of the rootstock had significant effects on the mineral composition of the petioles. Use of rootstocks with a genetic background including at least one Vitis riparia parent decreased the concentration of phosphorus and magnesium and increased the concentration of sulphur in the petioles of Cabernet-Sauvignon. Conclusion: Rootstocks with a Vitis riparia genetic background confer low petiolar concentrations of phosphorus and magnesium, and conversely, high petiolar concentration of sulphur. Significance of the study: The kind of rootstock onto which a grapevine has been grafted is known to influence the nutrient content of the scion. The results of the study show a significant relation between the genetic background of a rootstock and its ability to modify concentrations of phosphorus, magnesium and sulphur in the petioles of the scion under field conditions.

Climate change will impose increasingly warm and dry conditions on vineyards. Wine quality and yield are strongly influenced by climatic conditions and depend on complex interactions between temperatures, water availability, plant material, and viticultural techniques. In established winegrowing regions, growers have optimized yield and quality by choosing plant material and viticultural techniques according to local climatic conditions, but as the climate changes, these will need to be adjusted. Adaptations to higher temperatures include changing plant material (e.g., rootstocks, cultivars and clones) and modifying viticultural techniques (e.g., changing trunk height, leaf area to fruit weight ratio, timing of pruning) such that harvest dates are maintained in the optimal period at the end of September or early October in the Northern Hemisphere. Vineyards can be made more resilient to drought by planting drought resistant plant material, modifying training systems (e.g., goblet bush vines, or trellised vineyards at wider row spacing), or selecting soils with greater soil water holding capacity. While most vineyards in Europe are currently dry-farmed, irrigation may also be an option to grow sustainable yields under increasingly dry conditions but consideration must be given to associated impacts on water resources and the environment.

The influence of soil type and preparation on vine development and grape composition was investigated in a 50 ha estate located in Saint-Emilion (Bordeaux, France) and planted predominantly with Merlot. Part of the vineyard was planted down the slopes and another part of the vineyard was planted on terraces, where soils were profoundly modified through soil preparation. Grape composition (berry weight, sugar, total acidity, malic acid and pH), vigor (pruning weight), vine nitrogen status (Yeast Available Nitrogen (YAN) in grapes) and vine water status (δ13C) was measured at a very high density grid of 10 data points per hectare. Water deficit was globally weak over the estate because of high soil water holding capacity whereas vine nitrogen status was highly variable. Vine vigor and grape composition were predominantly driven by vine nitrogen status. On terraces, where soils were deep, due to invasive soil preparation, water deficits were particularly small or non-existent and vine nitrogen status was highly variable. Grape quality potential was medium to low, except in places with low nitrogen status, but at the expense of low yields. On parcels planted down the slopes water deficits were recorded because vine rooting was limited by compact subsoils. Vine nitrogen status was homogeneous. Grape quality and yield were medium to high and relatively homogeneous. When possible, downhill plantations are to be preferred over terraces because in the latter vine yield and quality parameters are highly variable because of massive soil movements prior to plantation.