Academic literature on the topic 'Grapevine, drought, rootstocks'

Recent and severe droughts in major grape (Vitis)-growing regions of the United States and Australia underscore the importance of more efficient agricultural use of water. Grape rootstock breeding for increased drought tolerance could contribute to continued sustainable yields as fresh water supplies decline. Rhizotron containers were used in a greenhouse to investigate the predictive measures of drought tolerance in young grapevine rootstocks. Deeper rooting distributions were found for the drought-tolerant rootstocks ‘110R’ (Vitis berlandieri × Vitis rupestris) and ‘Ramsey’ (Vitis champinii, a natural hybrid of Vitis candicans × V. rupestris) as opposed to shallower distributions observed in the more drought-sensitive rootstocks ‘101-14Mgt’ (Vitis riparia × V. rupestris) and ‘Riparia Gloire’ (V. riparia). Production of new roots during a 6-day nonirrigated period declined 45% to 53% for ‘Riparia Gloire’ and ‘101-14Mgt’, respectively, but showed no change in ‘110R’ and ‘Ramsey’. Slow growth, a hallmark of abiotic stress tolerance, was evident in the drought-tolerant rootstocks in their relatively slow shoot growth before drought stress and their relatively slow new root growth during recovery, especially for ‘Ramsey’. High stomatal conductance (gS) corresponded with drought tolerance and distinguished rootstocks best during the first 3 days of recovery, with a mean value for ‘Ramsey’ 2.7 times higher than ‘101-14Mgt’. Stomatal conductance during recovery may serve as the most efficient means of predicting drought tolerance capacity in a breeding program.

Abstract Background and Aims Living root tissues significantly constrain plant water uptake under drought, but we lack functional traits to feasibly screen diverse plants for variation in the drought responses of these tissues. Water stress causes roots to lose volume and turgor, which are crucial to root structure, hydraulics and growth. Thus, we hypothesized that root pressure–volume (p–v) curve traits, which quantify the effects of water potential on bulk root turgor and volume, would capture differences in rootstock drought tolerance. Methods We used a greenhouse experiment to evaluate relationships between root p–v curve traits and gas exchange, whole-plant hydraulic conductance and biomass under drought for eight grapevine rootstocks that varied widely in drought performance in field trials (101-14, 110R, 420A, 5C, 140-Ru, 1103P, Ramsey and Riparia Gloire), grafted to the same scion variety (Vitis vinifera ‘Chardonnay’). Key Results The traits varied significantly across rootstocks, and droughted vines significantly reduced root turgor loss point (πtlp), osmotic potential at full hydration (πo) and capacitance (C), indicating that roots became less susceptible to turgor loss and volumetric shrinkage. Rootstocks that retained a greater root volume (i.e. a lower C) also maintained more gas exchange under drought. The rootstocks that previous field trials have classified as drought tolerant exhibited significantly lower πtlp, πo and C values in well-watered conditions, but significantly higher πo and πtlp values under water stress, than the varieties classified as drought sensitive. Conclusions These findings suggest that acclimation in root p–v curve traits improves gas exchange in persistently dry conditions, potentially through impacts on root hydraulics or root to shoot chemical signalling. However, retaining turgor and volume in previously unstressed roots, as these roots deplete wet soil to moderately negative water potentials, could be more important to drought performance in the deep, highly heterogenous rooting zones which grapevines develop under field conditions.

The effects of root inoculation with mycorrhizal fungi (Glomus mosseae) on the water relations and carbon dioxide assimilation rates of grapevine (Vitis vinifera cv. Cabernet Sauvignon) plants are reported. Cuttings of Cabernet Sauvignon were grafted onto eight different grapevine rootstocks and the composite plants were grown in pots. The potting media of half the pots of each rootstock were inoculated with Glomus mosseae. Half of each of the inoculated and the non-inoculated pots were subjected to five-day and eight-day drought periods. The control (non-stressed plants) was watered throughout the experiment three times per week to maintain pot media close to field capacity. Foliar growth, leaf phosphorus concentrations and drought tolerance were greater in the inoculated than in the non-inoculated plants. After five days of drought stress, predawn leaf water potentials ranged between −0.5 and −1.07 MPa in non-mycorrhizal vines and between −0.32 MPa and −0.61 MPa in mycorrhizal vines. Similarly, net carbon dioxide assimilation rates in five-day stressed plants ranged from 1.5 to 4.6 μmol m−2 s−1, and from 2.9 to 6.1 μmol m−2 s−1 respectively. Some drought-sensitive rootstocks (775P, 101–14Mgt and 5BB) infected with mycorrhizal fungi and subjected to drought for eight days showed much-improved drought resistance compared with non-infected rootstocks of the same varieties. In drought-stressed plants, differences between the various rootstocks were significant. For example, rootstocks 110R, 140Rug, 1103P and 44–53 M had the highest predawn leaf water potentials and photosynthetic rates after five days of drought, independent of the mycorrhizal infection. These findings show that colonization of the root system by mycorrhizal fungi, may improve the water status of non-irrigated vines.

Cultivars of grapevine are commonly grafted onto rootstocks to improve resistance against biotic and abiotic stress, however, it is not clear whether known differences in hydraulic traits are conferred from rootstocks to a common scion. We recently found that Vitis riparia and Vitis champinii differed in drought-induced embolism susceptibility and repair, which was related to differences in root pressure generation after rewatering (Knipfer et al. 2015). In the present study, we tested whether these and other physiological responses to drought are conferred to a common V. vinifera scion (Cabernet Sauvignon) grafted on V. riparia and V. champinii rootstocks. We measured xylem embolism formation/repair using in vivo microCT imaging, which was accompanied with analysis of leaf gas exchange, osmotic adjustment and root pressure. Our data indicate that differences in scion physiological behaviour for both rootstock combinations were negligible, suggesting that the sensitivity of Cabernet Sauvignon scion to xylem embolism formation/repair, leaf gas exchange and osmotic adjustment is unaffected by either V. riparia or V. champinii rootstock in response to drought stress.

Due to the expansion of phylloxera into European vineyards rootstocks became an integral part of successful modern growing of grapevine. Breeding of rootstocks and their selection for resistance against both biotic and abiotic factors can be classified as a biotechnology. In this respect, the ca­pa­bi­li­ty of grapevine plants to adapt themselves to pedological conditions, especially to drought and a high content of lime (or factors inducing their chlorosis) represents a very important breeding goal. In this survey possible causes of lime-induced chlorosis and drought damage and their consequences are analysed. Some important drought-and-lime induced chlorosis-related properties of some selected rootstocks are mentioned as well.

Most of the vineyards around the world are in areas characterized by seasonal drought, where water deficits and high temperatures represent severe constraints on the regular grapevine growth cycle. Although grapevines are well adapted to arid and semi-arid environments, water stress can cause physiological changes, from mild to irreversible. Screening of available Vitis spp. genetic diversity for new rootstock breeding programs has been proposed as a way for which new viticulture challenges may be faced. In 2014, novel genotypes (M-rootstocks) were released from the University of Milan. In this work, the behavior of M1, M3 and M4 in response to decreasing water availabilities (80%, 50% and 20% soil water content, SWC) was investigated at the physiological and gene expression levels, evaluating gas exchange, stem water potential and transcript abundances of key genes related to ABA (abscisic acid) biosynthesis (VvZEP, VvNCED1 and VvNCED2) and signaling (VvPP2C4, VvSnRK2.6 and VvABF2), and comparing them to those of cuttings of nine commercial rootstocks widely used in viticulture. M-rootstocks showed a change at physiological levels in severe water-stressed conditions (20% soil water content, SWC), reducing the stomatal conductance and stem water potential, but maintaining high photosynthetic activity. Water use efficiency was high in water-limiting conditions. The transcriptional changes were observed at 50% SWC, with an increment of transcripts of VvNCED1 and VvNCED2 genes. M-rootstocks showed similar behavior to 1103P and 110R rootstocks, two highly tolerant commercial genotypes. These rootstocks adopted a tolerant strategy to face water-stressed conditions.

Some grapevine rootstocks perform better than others during and after drought events, yet it is not clear how inherent and stress-induced differences in root morphology and anatomy along the length of fine roots are involved in these responses. Using a variety of growing conditions and plant materials, we observed significant differences in root diameter, specific root length (SRL) and root diameter distribution between two commonly used commercial grapevine rootstocks: Richter 110 (110R; drought resistant) and Millardet et de Grasset 101-14 (101-14Mgt; drought sensitive). The 110R consistently showed greater root diameters with smaller SRL and proportion of root length comprised of fine lateral roots. The 110R also exhibited significantly greater distance from tip to nearest lateral, longer white root length, and larger proportion of root length that is white under drought stress. Mapping of fine root cortical lacunae showed similar patterns between the rootstocks; mechanical failure of cortical cells was common in the maturation zone, limited near the root tip, and increased with drought stress for both genotypes; however, lacuna formed under wetter soil conditions in 110R. Results suggest that drought resistance in grapevine rootstocks is associated with thick, limitedly branched roots with a larger proportion of white-functional roots that tend to form lacuna under more mild water deficit, all of which likely favor continued resource acquisition at depth.

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.

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 (AN), stomatal conductance (gs), and hydraulic conductance (Khplant) 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 gs, 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.

Extended Abstract ECO-PHYSIOLOGICAL CHARACTERIZATION OF NEW GRAPEVINE ROOTSTOCKS UNDER DROUGHT STRESS The objectives of grapevine rootstock breeding selections have undergone a continuous evolution over the years. From the first American vine species introduced to face the invasion of phylloxera and the mildews through Europe, recent breeding programmes aims to obtain plants which are also tolerant to biotic and abiotic stresses such as nematodes, drought and salt stress. Furthermore, the main present interest is on rootstocks that show good performance in different places and in favorable years, but that maintain a good efficiency in difficult conditions. The selection of grapevine rootstocks for resistance to drought conditions is particular important across the activities of modern breeding. Water stress tolerance but above all the water use efficiency (WUE) is becoming more and more important cause the variability of the environmental factors such as limited availability and irregular distribution of water resource. The achievement of the objectives of selection is closely linked to the efficiency and quality of characterization of the phenotype under stress conditions. Traditional phenotyping techniques, although consolidate and widespread, showed considerable limitations like time-consuming and destructive methods. Current technologies allow the development of new systems named high-throughput phenotyping techniques. Thermography, detecting heat patterns in the infrared-wavelength spectrum, is one of the techniques applied in viticulture to assess the plant water conditions. In addition to phenomics techniques, the detection of changes at the molecular level related to the ability to modify the phenotype under stress also play key roles. The analysis of the changes in gene expression induced by water stress is part of this evolution and the analyses of the transcriptional regulation of some genes involved in the responses to water deficiency shown particular interests. The present work aims to characterize the eco-physiological responses of new grapevine rootstocks under water stress in comparisons with the most widespread commercial rootstocks and other genotypes of Vitis spp. In particular the study focuses on the strategies in response to water stress and how these modifications can be transmitted to the scion by the rootstock. The first goal achieved has been the validation of the methods used in high-throughput phenotyping. Thermography has proven a valuable tool in order to assess the water condition of the plant and its evolution during the experiments. The effects of water stress on the variation of stomatal conductance and the rate of growth of the plants have been confirmed allowing the acceleration in phenotyping. It was also possible classify the different behaviors in response to water stress conditions providing a database of phenotypic information to be associated with genotypic data. This point has been particularly important as support to genetic association studies (GWAS) aimed to develop molecular markers to assist and optimize future breeding programs of grapevine rootstock. Another aspect observed is how the rootstock is able to influence some of the main responses to water stress and how these effects characterize the behavior of grafted variety. In particular several combinations of rootstock with the same scion have been compared: five of the most widespread commercial rootstocks and four new developed rootstocks has been tested under a dry down experiment under controlled greenhouse conditions. Changes in the eco-physiological status of plants in response to different levels of water stress has been evaluated. The rootstocks have been able to influence the responses to water stress in terms of stomatal conductance (Gs), net photosynthesis (Pn) and stem growth rate (SGR). The modification of gene expression in the roots of the different rootstocks and in the leaves of the scions have also been determined. The differences were observed on transcripts involved in the phenylpropanoid biosynthesis and relative transcription factors involved in the regulation of this pathway, stilbene synthases pathway and on the expression of abscisic acid (ABA) related genes. The analysis of transcriptional regulation of secondary metabolism has been considered as the main responses involved in the role of protection against oxidative stress induced by drought conditions. In conclusion, the rootstock has determined a different response according to the genotype but also was able to develop different responses in the scion. This shows that the biosynthetic pathways of ABA, stilbene and flavonoids synthases involved in scion response to drought conditions can be controlled by the rootstock.

Thesis (PhD(Agric))--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Water scarcity is a key limiting factor for viticulture in dry regions. Traditionally drought sensitive varieties have the potential to grow in dry areas, however in most situations, through the use of rootstocks. Drought-tolerant rootstocks are expected to improve grapevine response to water deficit by improving the water uptake and transport and by reducing the water loss in leaves by root-to-shoot signalling. The mechanisms of rootstocks’ tolerance to drought are not yet fully understood. The main aim of this study was to improve the understanding of the rootstock/scion-cultivar interaction in the regulation of grapevine water use and leaf stomatal behaviour. Irrigated field vines without any water constraint were compared to rain-fed grapevines subjected to moderate water constraint. To better manage vine water status, reduce variability, and compare more rootstocks, greenhouse trials were also conducted where plants were well watered or subjected to severe water constraints. Pinotage grapevines (Vitis vinifera L.) grafted onto 110 Richter, 140 Ruggeri and 1103 Paulsen rootstocks were used for field experiments whereas Pinotage grapevines grafted onto 99 Richter, 110 Richter, 140 Ruggeri, 1103 Paulsen and Ramsey were used for greenhouse experiments. Our study suggested the influence of rootstocks on scion-cultivar water status and leaf stomatal size and density and gas exchange of the scion, implying an influence on water uptake and transport and a tight regulation of the stomatal conductance. Our data supported the hypothesis that the influence of rootstock in response to drought seemed to be higher under increasing water deficit up to a point where the plant water status is the main driver of the stomatal conductance and therefore photosynthesis regulation, considering the plant water status thresholds. In addition, the results suggested that stomatal development is affected by light, drought and possibly by rootstocks. Nevertheless, it is still not clear how the rootstock affects stomatal development and the link with scion-cultivar water use. It seems that the transpiration rate of leaves is more related to stomatal size than density. Thus one possible mechanism of Pinotage leaf adaptation to water constraints was structural during leaf growth, with a reduction in pore size to reduce plant water loss. The results showed that the rootstock is regulating the cultivar's stomatal size (anatomical changes during leaf growth) and functioning (stomatal regulation) through a complex signalling process. The effect of light on stomatal development is interesting in the context of canopy microclimate and canopy manipulation (choice of the vine architecture vs canopy size, in the context of climate change versus the possible increase in drought and water scarcity). The use of rootstocks is a long term investment which aims to provide resistance to soil pests and pathogens and to confer to the scion-cultivar drought and salt tolerance. The use of drought tolerant rootstocks is actually one of the most relevant practical solutions in dry terroir – units and in situations where water availability is limited. The understanding of the physiological and genetic mechanisms which govern scion-cultivar drought tolerance/behaviour induced by rootstocks is critical in terms of rootstocks choice in interaction with the scion-cultivar and is critical to assist breeding programs to create/select drought tolerant rootstocks.

Grapevine is worldwide grafted on rootstocks to create a biological barrier to the phylloxera (Daktulosphaira vitifoliae). Despite the key role of rootstock in the adaptation to environmental conditions, a limited number of genotypes is available for winegrowers, showing a narrow genetic background. The gap between the importance of rootstocks in abiotic stress tolerance and their low genetic variability leads to consider rootstock breeding as a promising strategy to face climate change. In the last decades, new breeding programs were developed with the aim to provide new rootstocks able to cope with drought and other abiotic stresses. Nowadays, the continuous progress in genetic techniques can assist and accelerate the selection process of new tolerant genotypes. In the present PhD project, several genotypes at different stages in rootstock selection process were analyzed for drought tolerance. The first part of the thesis focused on 3 genotypes belonging to the recent M-series, the second part was about a new selection of 30 genotypes, coming from different breeding programs, and in the last part a breeding population of 141 genotypes was used for a genome wide association study (GWAS). The new M-rootstocks (M1, M3 and M4), recently placed on the market, were compared to traditional rootstocks, in order to better understand their behavior under drought. In a pot experiment under controlled conditions, M1, M3 and M4 were compared to nine rootstocks with different genetic background at decreasing levels of water availability. M-rootstock performance under water deficit was similar to the tolerant rootstocks 1103P and 110R, in both phenotypic and genetic responses to water stress. These rootstocks adopted a strategy of tolerance to face water stress, increasing the water use efficiency (WUE) under deficit conditions. To deeply investigate the behavior of tolerant rootstocks under drought, a second experiment in semi-controlled conditions was set up, comparing M4 to 1103P under progressive water deficit, in grafting combination with V. vinifera cv Pinot Blanc. Similar performances were reported by the two grafting combinations under mild to moderate water deficit, but a different response occurred under sever conditions: 1103P reduced stomatal conductance, transpiration, and carbon assimilation more than M4, which was able to preserve water use efficiency and operating efficiency of photosystem II. In the second part of the thesis 30 new selected genotypes were compared to rootstock M2 for water stress tolerance and nutritional status, in order to characterize the rootstock material before the marketing process and to identify new pre-breeding material. The experiment was carried out in un-grafted conditions for two years and in two experimental fields, characterized by different water availability. Several parameters were analyzed, such as transpiration, WUE, vigor, macronutrients and micronutrients in the leaves. Genotypes ranked for both abiotic stresses and the differences between the two sites allowed to estimate their plasticity for each trait. Finally, a GWA approach was applied on a breeding population, counting 141 genotypes, in order to identify the genomic regions involved in drought tolerance. The population was genotyped with a 18k SNP array, after the validation on non-vinifera germplasm, belonging to a rootstock core-collection of 70 genotypes. Three phenotyping cycles under increasing water deficit were performed on the breeding population under greenhouse-controlled conditions. Vigor, shoot growth rate, transpiration, stomatal conductance and leaf turgor were estimated for each genotype at different water deficit levels. A group of tolerant genotypes with high performance under water deficit condition was identified and used in GWAS approach to detect the loci associated to drought tolerance of rootstocks. In conclusion, this work enhanced the knowledge about rootstock response to water deficit, characterized the water tolerance of a large panel of rootstocks and identified potential target genes for future breeding programs.

Dans le contexte du changement climatique, les prédictions réalisées mettent en évidence une altération de la disponibilité en eau dans de nombreuses régions viticoles ; ce qui, conjointement à l’augmentation de la population mondiale et la diminution des terres agricoles, va accroître la compétition pour l’utilisation des ressources hydriques. Par conséquent, améliorer l'adaptation à la sécheresse de la vigne est un des enjeux majeurs des prochaines années. Pour cela, une adaptation des pratiques culturales peut être proposée, en particulier le choix pertinent du matériel végétal et notamment du porte-greffe.Dans ce travail, le rôle du porte-greffe vis-à-vis de la réponse de la vigne greffée à la contrainte hydrique a été étudié, en utilisant des approches écophysiologiques, moléculaires et de modélisation. Des expériences ont été réalisées en conditions contrôlées afin d’étudier l’effet du déficit hydrique à court et long terme sur les réponses de différents porte-greffes greffés avec le même scion.Le modèle écophysiologique a démontré que les porte-greffes affectent l'ouverture stomatique du greffon par des processus coordonnés incluant les caractéristiques racinaires, les signaux hydrauliques et les signaux chimiques lors d’un déficit hydrique à court terme. La conductance stomatique, le taux de transpiration et la conductance hydraulique des feuilles ont été plus élevés en conditions irriguées et de stress hydriques modérés chez le génotype résistant à la sécheresse (110 Richter) par rapport au génotype sensible à la sécheresse (Vitis riparia cv. Gloire de Montpellier). Nous avons identifié plusieurs paramètres génétiques impliqués dans le contrôle de la régulation stomatique. Des différences d’architecture racinaire et de conductivité hydraulique des racines ont été identifiées entre les porte-greffes.Le déficit hydrique à long terme a entrainé des réponses adaptatives différentes entre les porte-greffes. Le génotype tolérant la sécheresse a induit une modification du diamètre des vaisseaux du xylème de la partie apicale de la racine en réponse au déficit hydrique modéré tandis que le génotype sensible n'a pas présenté de différence par rapport au contrôle. L’analyse transcriptomique des racines a identifié des gènes spécifiques aux différents génotypes, qui sont régulés en fonction du niveau de déficit hydrique. La comparaison entre les niveaux de stress et les génotypes a identifié 24 gènes intervenant dans l’interaction « traitement × génotype ». Ces gènes sont majoritairement impliqués dans le métabolisme des lipides et de la paroi cellulaire. Des courbes de réponse au déficit hydrique spécifiques aux différents génotypes ont été observées. La protection contre les dommages liés aux stress oxydatifs induits par le stress hydrique semble être un mécanisme important chez le porte-greffe résistant à la sécheresse. Le génotype sensible semble répondre au déficit hydrique par une modification des propriétés de la paroi cellulaire de la racine
Climate change raises concerns about temporal and spatial water availability in many grape growing countries. The rapidly increasing world population and the scarcity of suitable land for agricultural food production, together with a changing climate, will increase competition with grape-producing areas for the use of land and resources. Consequently, other practices that can potentially improve water management of vineyards and water acquisition by grapevines need to be considered. Aside from canopy systems and their management, the choice of plant material is a key issue. Therefore, in the present work, the role of different rootstocks, regarding their tolerance to drought, was investigated for their potential effects on i) water uptake, ii) water transport and iii) shoot water use, using a combination of ecophysiological, modelling and transcriptomic approaches. Experiments were conducted under controlled conditions to decipher short and long term responses to drought of different rootstocks grafted with the same scion. An ecophysiological model was used to investigate the roles of rootstock genotypes in the control of stomatal aperture. Long-term steady state water-deficit conditions were used to examine the responses of i) whole plant growth, root anatomy and hydraulic properties and ii) transcriptome remodelling in the roots.Our model showed that rootstock affect stomatal aperture of the grafted scion via coordinated processes between root traits, hydraulic signals and chemical signals. Stomatal conductance, transpiration rate and leaf-specific hydraulic conductance were higher and better maintained under well-watered and moderate water-deficit conditions in the drought-tolerant genotype (110 Richter) compared to the drought-sensitive one (Vitis riparia cv. Gloire de Montpellier). We identified several genotype-specific parameters which play important roles, like root-related parameters, in the control of stomatal regulation. Additionally, root system architecture and root hydraulic properties are important constitutive traits identified between rootstocks.Long-term water-deficit induced genotype adaptive responses in the roots were evaluated. The drought-tolerant genotype exhibited a substantial shift in root tips xylem conduit diameter under moderate water-deficit while the drought-sensitive genotype did not respond. Transcriptomic analysis identified genotype-specific transcripts that are regulated by water-deficit levels. The comparison between stress levels and genotypes identified 24 significant genes in “treatment×genotype” interactions, most of them were involved in lipid metabolism and cell wall processes. These genes displayed genotype-specific water-deficit response curves. Protection against drought-induced oxidative damage was found to be an important mechanisms induced by the drought-tolerant rootstock, while the drought-sensitive one responds to water-deficit by modification of cell wall properties

More than 80% of vineyards around the world use grafted plants: a scion of Vitis vinifera grafted onto a rootstock of single or interspecific hybrids of American Vitis species, resistant or partially resistant to Phylloxera (Daktulosphaira vitifoliae (Fitch, 1856)). The genetic variability of grapevine rootstocks plays a fundamental role in their adaptation to the environment (Serra et al., 2013). In the climate change scenario, predicting an increase of aridity in the near future (Dai, 2013), the more frequent and severe drought events may represent the major constrain for the future of viticulture (IPCC, 2018; Schultz, 2000). Therefore, the selection of new rootstocks able to cope with unfavourable environmental condition is a key asset, as well as a strategy to improve crop yield/vegetative growth balance on scion behaviour (Corso and Bonghi, 2014). So far, the influence of rootstock on scion physiological performance during water stress has always aroused great interest. On the contrary, the scion impact on rootstock response is still less debated. Therefore, the effect of grafting on rootstock behaviour have been investigated. Phenotypical and large-scale whole transcriptome analyses on two genotypes, a drought-susceptible (101-14) and a drought-tolerant (1103 P), own-rooted and grafted with Cabernet Sauvignon, subjected to a gradual water shortage in semi-controlled environmental conditions have been performed. The ungrafted condition affected photosynthesis and transpiration, meaning the decisive role of scion in modulation of gas exchanges and in general in plant adaptation. Molecular evidence highlighted that the scion delays the stimulus perception and rootstock reactivity to drought. Since 1985, the DiSAA research group operating at the University of Milan is carrying on a rootstock crossbreeding program which has led to the release of four genotypes: M1, M2, M3 and M4. They show from moderate to high tolerance to drought (M4 > M1 = M3 > M2). In order to characterize their performance during water stress, their physiological (gas exchanges and stem water potential) and transcriptome response (genes involved in ABA-synthesis and ABA-mediated responses to drought) under well-watered and water stress conditions were examined. The behaviour of M-rootstocks (M1, M2 and M3) was compared with that of other commercial genotypes largely used in viticulture, either tolerant (140 Ru, 41 B, 110 R, 1103 P), less tolerant (SO 4, K 5BB) and susceptible (420 A and Schwarzman). Discriminant analysis (DA) showed that when water availability starts to decrease, rootstocks firstly perceives the stress activating a transcriptome response, consequently physiological changes have been observed. It also demonstrated that the three M-rootstocks were clearly discriminated: M4 was grouped with the most tolerant genotypes while M3 with the less tolerant or susceptible ones from a physiological standpoint, confirming their different attitude to tolerate water stress. M4 has proven to be a promising rootstock due to its ability to adapt to drought conditions. Considering the constant great demand for vine planting materials, the obtainment of genetically homogeneous populations (i.e. clones) from elite individuals through micropropagation represents a rapid alternative to conventional multiplication. For this reason, an efficient high-throughput protocol for M4 in vitro propagation was set up. Its attitude to shooting, root development and callus proliferation was compared to that of other rootstocks largely used in viticulture (K5BB, 1103P, 101-14 and 3309C). Moreover, pro-embryogenic and embryogenic callus from bud explants were also produced, representing a cellular material manipulable with the genetic engineering techniques. In water scarcity condition, among the mechanisms activated by M4, the great ability to scavenge ROS, related to the increased accumulation of stilbenes and flavonoids, may be such as to give it tolerance to the stress. In particular, the higher levels of trans-resveratrol were correlated with the up-regulation of some stilbene synthase genes, mainly VvSTS16, VvSTS18, VvSTS27 and VvSTS29. The over expression of these genes was linked to a structural variation in their promoter region. To confirm that VvSTSs genes may be considered putative factors of M4 better adaptation to water stress, a genome editing protocol based on the CRISPR/Cas9 system, aimed at knock-out the genes, was performed. For testing the gRNAs functionality, a transient assay on in vitro micropropagated plantlets of M4 and 101-14 was performed. The positive results obtained by this experiment will lead to the transformation of somatic embryos and regeneration of whole-edited plants using the vectors developed.

Consequences of climate change are becoming markedly worrying, since average surface temperatures are constantly going up and extreme climatic events are getting more frequent and intense, posing a considerable threat to worldwide viticulture. Among different abiotic stresses, drought is the factor that has a greater influence on plant physiology with a drastic impact on grape yield and quality. To overcome the deleterious effects of drought, plants adopt a multitude of physiological, biochemical and molecular mechanisms at cellular and systemic levels. Therefore, understanding the complexity of plant’s response to water deficit represents a major challenge for sustainable winegrowing. Especially, the development of strategies to reduce water consumption and to improve water-use efficiency (WUE) in vines will be fundamental in future years. Furthermore, the regulation of water use is particularly influenced by rootstocks, on which cultivars are generally grafted to cope with phylloxera infestations. The adaptation to drought indeed seems to be a cooperative action between scions and rootstocks, by means of hydraulic conductivity, chemical signalling and exchange of genetic material. However, a very few number of works were focused on identifying the genetic regions of grape rootstocks responsible for drought tolerance mechanisms. In this regard, the present research aimed to identify genetic determinism of phenotypic traits associated with drought tolerance. A genome-wide association study (GWAS) approach has been applied on an ‘ad hoc’ association mapping panel including different Vitis species, in order to dissect the genomic bases of transpiration-related traits and to identify genetic regions of grape rootstocks involved in drought tolerance, thereby potentially relevant for crop improvement. The panel was first genotyped with the commercial GrapeReSeq Illumina 20K SNP array and infrared thermography has been applied to estimate stomatal conductance values and to assess water status during progressive water stress and re-watering in two years. Some significant marker-trait associations were detected and a good list of candidate genes with a feasible role in drought response were identified. The physiological responses to drought were further investigate in four commercial rootstocks, 101.14 Millardet et de Grasset (V. riparia x V. rupestris), Selection Oppenhiem 4 (V. riparia x V. berlandieri), 110 Richter (V. rupestris x V. berlandieri) and Riparia Gloire de Montpellier (V. riparia). Differences were observed among genotypes and between water stress experiments that were performed in pots and in hydroponics. Furthermore, the application of osmotic stress in a hydroponic system has proved to be a useful method to evaluate the short-term stress response, especially for a rapid screening of stomatal sensitivity. In addition, a pilot study on a reduced subset of Vitis sylvestris genotypes exposed to water deficit treatment was carried out to evaluate their drought tolerance, because they represent a source of natural genetic diversity that could be exploited for future breeding programs. Taken together, a step forward to understand the basis of genetic variability of the response to water deprivation in grape rootstocks has been done in the present research. Moreover, it has been proved that different phenotyping approaches may help to dissect a highly complex trait such as water stress response.