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.

Genome editing of a recalcitrant wine grape genotype by lipofectamine-mediated delivery of CRISPR/Cas9 ribonucleoproteins to protoplasts.

The main bottleneck in the application of biotechnological breeding methods to woody species is due to the in vitro regeneration recalcitrance shown by several genotypes. On the other side, woody species, especially grapevine (Vitis vinifera L.), use most of the pesticides and other expensive inputs in agriculture, making the development of efficient approaches of genetic improvement absolutely urgent. Genome editing is an extremely promising technique particularly for wine grape genotypes, as it allows to modify the desired gene in a single step, preserving all the quality traits selected and appreciated in elite varieties. A genome editing and regeneration protocol for the production of transgene-free grapevine plants, exploiting the lipofectamine-mediated direct delivery of CRISPR-Cas9 ribonucleoproteins (RNPs) to target the phytoene desaturase gene, is reported. We focused on Nebbiolo (V. vinifera), an extremely in vitro recalcitrant wine genotype used to produce outstanding wines, such as Barolo and Barbaresco. The use of the PEG-mediated editing method available in literature and employed for highly embryogenic grapevine genotypes did not allow the proper embryo development in the recalcitrant Nebbiolo. Lipofectamines, on the contrary, did not have a negative impact on protoplast viability and plant regeneration, leading to the obtainment of fully developed edited plants after about 5 months from the transfection. Our work represents one of the first examples of lipofectamine use for delivering editing reagents in plant protoplasts. The important result achieved for the wine grape genotype breeding could be extended to other important wine grape varieties and recalcitrant woody species.

A novel RAV transcription factor from pear interacts with viral RNA-silencing suppressors to inhibit viral infection.

In plants, RNA silencing constitutes a strong defense against viral infection, which viruses counteract with RNA-silencing suppressors (RSSs). Understanding the interactions between viral RSSs and host factors is crucial for elucidating the molecular arms race between viruses and host plants. We report that the helicase motif (Hel) of the replicase encoded by apple stem grooving virus (ASGV)-the main virus affecting pear trees in China-is an RSS that can inhibit both local and systemic RNA silencing, possibly by binding double-stranded (ds) siRNA. The transcription factor related to ABSCISIC ACID INSENSITIVE3/VIVIPAROUS1 from pear (PbRAV1) enters the cytoplasm and binds Hel through its C terminus, thereby attenuating its RSS activity by reducing its binding affinity to 21- and 24-nt ds siRNA, and suppressing ASGV infection. PbRAV1 can also target p24, an RSS encoded by grapevine leafroll-associated virus 2 (GLRaV-2), with similar negative effects on p24's suppressive function and inhibition of GLRaV-2 infection. Moreover, like the positive role of the PbRAV1 homolog from grapevine (VvRAV1) in p24's previously reported RSS activity, ASGV Hel can also hijack VvRAV1 and employ the protein to sequester 21-nt ds siRNA, thereby enhancing its own RSS activity and promoting ASGV infection. Furthermore, PbRAV1 neither interacts with CP, an RSS encoded by grapevine inner necrosis virus, nor has any obvious effect on CP's RSS activity. Our results identify an RSS encoded by ASGV and demonstrate that PbRAV1, representing a novel type of RAV transcription factor, plays a defensive role against viral infection by targeting viral RSSs.

VvbHLH036, a basic helix-loop-helix transcription factor regulates the cold tolerance of grapevine.

Cold stress is an adverse environmental factor that limits the growth and productivity of horticulture crops such as grapes (Vitis vinifera). In this study, we identified a grapevine cold-induced basic helix-loop-helix (bHLH) transcription factor (VvbHLH036). Overexpression and CRISPR/Cas9-mediated knockout (KO) of VvbHLH036 enhanced and decreased cold tolerance in grapevine roots, respectively. Transcriptome analysis of VvbHLH036-overexpressed roots identified threonine synthase (VvThrC1) as a potential downstream target of VvbHLH036. We confirmed that VvbHLH036 could bind the VvThrC1 promoter and activate its expression. Both the transcripts of VvThrC1 and the content of threonine were significantly induced in the leaves and roots of grapevine under cold treatment compared to controls. Conversely, these dynamics were significantly suppressed in the roots of CRISPR/Cas9-induced knockout of VvbHLH036. These observations support the regulation of threonine accumulation by VvbHLH036 through VvThrC1 during cold stress in grapevine. Furthermore, overexpression and CRISPR/Cas9-mediated knockout of VvThrC1 also confirmed its role in regulating threonine content and cold tolerance in transgenic roots at low temperature. Exogenous threonine treatment increased cold tolerance and reduced the accumulation of superoxide anions and hydrogen peroxide in grapevine leaves. Together, these findings point to the pivotal role of VvbHLH036 and VvThrC1 in the cold stress response in grapes by regulating threonine biosynthesis.

Genome-wide DNA methylation dynamics and RNA-seq analysis during grape (cv. 'Cabernet Franc') skin coloration.

This study generated whole genome DNA methylation maps to characterize DNA methylomes of grape (cv. 'Cabernet Franc') skins and examine their functional significance during grape skin coloration. We sampled grape skin tissues at three key stages (the early stage of grape berry swelling, the late stage of grape berry swelling and the veraison) during which the color of grape berries changed from green to red. DNA methylation levels of grape skins at the three stages were higher in transposable element regions than in the genic regions, and the CG and CHG DNA methylation levels of the genic region were higher than the CHH DNA methylation levels. We identified differentially methylated regions (DMRs) in S2_vs_S1 and S3_vs_S1. The results indicated that DMRs predominantly occurred within the CHH context during grape skin coloration. Many gene ontology (GO)-enriched DMR-related genes were involved in "nucleotide binding," "catalytic activity" and "ribonucleotide binding" terms; however, many KEGG-enriched DMR-related genes were involved in the "flavonoid biosynthesis" pathway. Our results could provide an important foundation for future research on the development mechanism of grape berries.

Insights into the cell-wall dynamics in grapevine berries during ripening and in response to biotic and abiotic stresses.

The cell wall (CW) is the dynamic structure of a plant cell, acting as a barrier against biotic and abiotic stresses. In grape berries, the modifications of pulp and skin CW during softening ensure flexibility during cell expansion and determine the final berry texture. In addition, the CW of grape berry skin is of fundamental importance for winemaking, controlling secondary metabolite extractability. Grapevine varieties with contrasting CW characteristics generally respond differently to biotic and abiotic stresses. In the context of climate change, it is important to investigate the CW dynamics occurring upon different stresses, to define new adaptation strategies. This review summarizes the molecular mechanisms underlying CW modifications during grapevine berry fruit ripening, plant-pathogen interaction, or in response to environmental stresses, also considering the most recently published transcriptomic data. Furthermore, perspectives of new biotechnological approaches aiming at modifying the CW properties based on other crops' examples are also presented.

Epigenetic differences between wild and cultivated grapevines highlight the contribution of DNA methylation during crop domestication.

The domestication process in grapevines has facilitated the fixation of desired traits. Nowadays, vegetative propagation through cuttings enables easier preservation of these genotypes compared to sexual reproduction. Nonetheless, even with vegetative propagation, various phenotypes are often present within the same vineyard due to the accumulation of somatic mutations. These mutations are not the sole factors influencing phenotype. Alongside somatic variations, epigenetic variation has been proposed as a pivotal player in regulating phenotypic variability acquired during domestication. The emergence of these epialleles might have significantly influenced grapevine domestication over time. This study aims to investigate the impact of domestication on methylation patterns in cultivated grapevines. Reduced-representation bisulfite sequencing was conducted on 18 cultivated and wild accessions. Results revealed that cultivated grapevines exhibited higher methylation levels than their wild counterparts. Differential Methylation Analysis between wild and cultivated grapevines identified a total of 9955 differentially methylated cytosines, of which 78% were hypermethylated in cultivated grapevines. Functional analysis shows that core methylated genes (consistently methylated in both wild and cultivated accessions) are associated with stress response and terpenoid/isoprenoid metabolic processes. Meanwhile, genes with differential methylation are linked to protein targeting to the peroxisome, ethylene regulation, histone modifications, and defense response. Collectively, our results highlight the significant roles that epialleles may have played throughout the domestication history of grapevines.

The pathogenicity of Plasmopara viticola: a review of evolutionary dynamics, infection strategies and effector molecules.

Oomycetes are filamentous organisms that resemble fungi in terms of morphology and life cycle, primarily due to convergent evolution. The success of pathogenic oomycetes lies in their ability to adapt and overcome host resistance, occasionally transitioning to new hosts. During plant infection, these organisms secrete effector proteins and other compounds during plant infection, as a molecular arsenal that contributes to their pathogenic success. Genomic sequencing, transcriptomic analysis, and proteomic studies have revealed highly diverse effector repertoires among different oomycete pathogens, highlighting their adaptability and evolution potential.The obligate biotrophic oomycete Plasmopara viticola affects grapevine plants (Vitis vinifera L.) causing the downy mildew disease, with significant economic impact. This disease is devastating in Europe, leading to substantial production losses. Even though Plasmopara viticola is a well-known pathogen, to date there are scarce reviews summarising pathogenicity, virulence, the genetics and molecular mechanisms of interaction with grapevine.This review aims to explore the current knowledge of the infection strategy, lifecycle, effector molecules, and pathogenicity of Plasmopara viticola. The recent sequencing of the Plasmopara viticola genome has provided new insights into understanding the infection strategies employed by this pathogen. Additionally, we will highlight the contributions of omics technologies in unravelling the ongoing evolution of this oomycete, including the first in-plant proteome analysis of the pathogen.

From buds to shoots: insights into grapevine development from the Witch's Broom bud sport.

BACKGROUND: Bud sports occur spontaneously in plants when new growth exhibits a distinct phenotype from the rest of the parent plant. The Witch's Broom bud sport occurs occasionally in various grapevine (Vitis vinifera) varieties and displays a suite of developmental defects, including dwarf features and reduced fertility. While it is highly detrimental for grapevine growers, it also serves as a useful tool for studying grapevine development. We used the Witch's Broom bud sport in grapevine to understand the developmental trajectories of the bud sports, as well as the potential genetic basis. We analyzed the phenotypes of two independent cases of the Witch's Broom bud sport, in the Dakapo and Merlot varieties of grapevine, alongside wild type counterparts. To do so, we quantified various shoot traits, performed 3D X-ray Computed Tomography on dormant buds, and landmarked leaves from the samples. We also performed Illumina and Oxford Nanopore sequencing on the samples and called genetic variants using these sequencing datasets. RESULTS: The Dakapo and Merlot cases of Witch's Broom displayed severe developmental defects, with no fruit/clusters formed and dwarf vegetative features. However, the Dakapo and Merlot cases of Witch's Broom studied were also phenotypically different from one another, with distinct differences in bud and leaf development. We identified 968-974 unique genetic mutations in our two Witch's Broom cases that are potential causal variants of the bud sports. Examining gene function and validating these genetic candidates through PCR and Sanger-sequencing revealed one strong candidate mutation in Merlot Witch's Broom impacting the gene GSVIVG01008260001. CONCLUSIONS: The Witch's Broom bud sports in both varieties studied had dwarf phenotypes, but the two instances studied were also vastly different from one another and likely have distinct genetic bases. Future work on Witch's Broom bud sports in grapevine could provide more insight into development and the genetic pathways involved in grapevine.

Multiple deletions of candidate effector genes lead to the breakdown of partial grapevine resistance to downy mildew.

Grapevine downy mildew, caused by the oomycete Plasmopara viticola (P. viticola, Berk. & M. A. Curtis; Berl. & De Toni), is a global threat to Eurasian wine grapes Vitis vinifera. Although resistant grapevine varieties are becoming more accessible, P. viticola populations are rapidly evolving to overcome these resistances. We aimed to uncover avirulence genes related to Rpv3.1-mediated grapevine resistance. We sequenced the genomes and characterized the development of 136 P. viticola strains on resistant and sensitive grapevine cultivars. A genome-wide association study was conducted to identify genomic variations associated with resistant-breaking phenotypes. We identified a genomic region associated with the breakdown of Rpv3.1 grapevine resistance (avrRpv3.1 locus). A diploid-aware reassembly of the P. viticola INRA-Pv221 genome revealed structural variations in this locus, including a 30 kbp deletion. Virulent P. viticola strains displayed multiple deletions on both haplotypes at the avrRpv3.1 locus. These deletions involve two paralog genes coding for proteins with 800-900 amino acids and signal peptides. These proteins exhibited a structure featuring LWY-fold structural modules, common among oomycete effectors. When transiently expressed, these proteins induced cell death in grapevines carrying Rpv3.1 resistance, confirming their avirulence nature. This discovery sheds light on the genetic mechanisms enabling P. viticola to adapt to grapevine resistance, laying a foundation for developing strategies to manage this destructive crop pathogen.

Plasmopara viticola effector PvCRN20 represses the import of VvDEG5 into chloroplasts to suppress immunity in grapevine.

Chloroplasts play a crucial role in plant defense against pathogens, making them primary targets for pathogen effectors that suppress host immunity. This study characterizes the Plasmopara viticola CRN-like effector, PvCRN20, which interacts with DEG5 in the cytoplasm but not with its interacting protein, DEG8, which is located in the chloroplast. By transiently overexpressing in tobacco leaves, we show that PvCRN20 could inhibit INF1- and Bax-triggered cell death. Constitutive expression of PvCRN20 suppresses the accumulation of reactive oxygen species (ROS) and promotes pathogen colonization. PvCRN20 reduces DEG5 entry into chloroplasts, thereby disrupting DEG5 and DEG8 interactions in chloroplasts. Overexpression of VvDEG5 and VvDEG8 induces ROS accumulation and enhances grapevine resistance to P. viticola, whereas knockout of VvDEG8 represses ROS production and promotes P. viticola colonization. Consistently, ectopic expression of VvDEG5 and VvDEG8 in tobacco promotes chloroplast-derived ROS accumulation, whereas co-expression of PvCRN20 counteracted this promotion by VvDEG5. Therefore, DEG5 is essential for the virulence function of PvCRN20. Although PvCRN20 is located in both the nucleus and cytoplasm, only cytoplasmic PvCRN20 suppresses plant immunity and promotes pathogen infection. Our results reveal that PvCRN20 dampens plant defenses by repressing the chloroplast import of DEG5, thus reducing host ROS accumulation and facilitating pathogen colonization.

Phenotyping xylem connections in grafted plants using X-ray micro-computed tomography.

Plants are able to naturally graft or inosculate their trunks, branches and roots together, this mechanism is used by humans to graft together different genotypes for a range of purposes. Grafts are considered successful if functional vascular connections between the two genotypes occur. Various techniques can evaluate xylem connections across the graft interface. However, these methods are generally unable to assess the heterogeneity and three-dimensional (3D) structure of xylem vessel connections. Here we present the use of X-ray micro-computed tomography to characterize the 3D morphology of grafts of grapevine. We show that xylem vessels form between the two plants of natural root and human-made stem grafts. The main novelty of this methodology is that we were able to visualize the 3D network of functional xylem vessels connecting the scion and rootstock in human-made stem grafts thanks to the addition of a contrast agent to the roots and improved image analysis pipelines. In addition, we reveal the presence of extensive diagonal xylem connections between the main axial xylem vessels in 2-year old grapevine stems. In conclusion, we present a method that has the potential to provide new insights into the structure and function of xylem vessels in large tissue samples.

CRISPR/Cas9 editing of Downy mildew resistant 6 (DMR6-1) in grapevine leads to reduced susceptibility to Plasmopara viticola.

Downy mildew of grapevine (Vitis vinifera), caused by the oomycete Plasmopara viticola, is an important disease that is present in cultivation areas worldwide, and using resistant varieties provides an environmentally friendly alternative to fungicides. DOWNY MILDEW RESISTANT 6 (DMR6) from Arabidopsis is a negative regulator of plant immunity and its loss of function confers resistance to downy mildew. In grapevine, DMR6 is present in two copies, named VvDMR6-1 and VvDMR6-2. Here, we describe the editing of VvDMR6-1 in embryogenic calli using CRISPR/Cas9 and the regeneration of the edited plants. All edited plants were found to be biallelic and chimeric, and whilst they all showed reduced growth compared with non-transformed control plants, they also had reduced susceptibility to P. viticola. Comparison between mock-inoculated genotypes showed that all edited lines presented higher levels of salicylic acid than controls, and lines subjected to transformation presented higher levels of cis-resveratrol than controls. Our results identify VvDMR6-1 as a promising target for breeding grapevine cultivars with improved resistance to downy mildew.

The cysteine-rich receptor-like kinase CRK10 targeted by Coniella diplodiella effector CdE1 contributes to white rot resistance in grapevine.

Grape white rot is a devastating fungal disease caused by Coniella diplodiella. The pathogen delivers effectors into the host cell that target crucial immune components to facilitate its infection. Here, we examined a secreted effector of C. diplodiella, known as CdE1, which has been found to inhibit Bax-triggered cell death in Nicotiana benthamiana plants. The expression of CdE1 was induced at 12-48 h after inoculation with C. diplodiella, and the transient overexpression of CdE1 led to increased susceptibility of grapevine to the fungus. Subsequent experiments revealed an interaction between CdE1 and Vitis davidii cysteine-rich receptor-like kinase 10 (VdCRK10) and suppression of VdCRK10-mediated immunity against C. diplodiella, partially by decreasing the accumulation of VdCRK10 protein. Furthermore, our investigation revealed that CRK10 expression was significantly higher and was up-regulated in the resistant wild grapevine V. davidii during C. diplodiella infection. The activity of the VdCRK10 promoter is induced by C. diplodiella and is higher than that of Vitis vitifera VvCRK10, indicating the involvement of transcriptional regulation in CRK10 gene expression. Taken together, our results highlight the potential of VdCRK10 as a resistant gene for enhancing white rot resistance in grapevine.

NAC61 regulates late- and post-ripening osmotic, oxidative, and biotic stress responses in grapevine.

During late- and post-ripening stages, grape berry undergoes profound biochemical and physiological changes whose molecular control is poorly understood. Here, we report the role of NAC61, a grapevine NAC transcription factor, in regulating different processes involved in berry ripening progression. NAC61 is highly expressed during post-harvest berry dehydration and its expression pattern is closely related to sugar concentration. The ectopic expression of NAC61 in Nicotiana benthamiana leaves resulted in low stomatal conductance, high leaf temperature, tissue collapse and a higher relative water content. Transcriptome analysis of grapevine leaves transiently overexpressing NAC61 and DNA affinity purification and sequencing analyses allowed us to narrow down a list of NAC61-regulated genes. Direct regulation of the stilbene synthase regulator MYB14, the osmotic stress-related gene DHN1b, the Botrytis cinerea susceptibility gene WRKY52, and NAC61 itself was validated. We also demonstrate that NAC61 interacts with NAC60, a proposed master regulator of grapevine organ maturation, in the activation of MYB14 and NAC61 expression. Overall, our findings establish NAC61 as a key player in a regulatory network that governs stilbenoid metabolism and osmotic, oxidative, and biotic stress responses that are the hallmark of late- and post-ripening grape stages.

Combination of irradiated chitosan and microbial agent to reduce downy mildew on grapevine cv. Thompson seedless.

Globally sustainable disease management ensuring high quality in grapes is in demand as it holds significant importance as a versatile fruit for consumption, winemaking, and production of various products such as grape juice, raisin, and grape-seed oil. The present paper reports a combination of nano-biotechnology as a promising strategy for enhancing plant health and fruit productivity in grapes combining Irradiated chitosan nanoparticles and bio-control agents. The Irradiated Chitosan with Bacillus subtilis and Trichoderma viridae and pesticides were evaluated for disease management. Percent disease index, percent disease control, and percent yield enhancement in Cymoxanil 8% + Mamcozeb 64% WP @ 0.2% treatment were as 17. 24%, 67.97% and 33.91% in 150 ppm Irradiated chitosan+B. subtilis were 19.83, 63.16, 30.41 and in Trichoderma 150 ppm Irradiated chitosan were 24.58, 54.33, and 27.40, respectively as compared to untreated crop with disease severity 53.84% PDI. Thus, irradiated chitosan and Bacillus subtilis elucidated a synergistic combination for residue-free efficient phytosanitary measures, which harnessed the strength of chitosan and bio-control agents for sustainable grape productivity. These findings will also pave the way for a deeper understanding of the synergistic interaction between Irradiated nanochitosan and bio-control agents for an eco-friendly and economically viable disease management strategy. The minimum temperature and morning relative humidity (RH I) had positive significance, with correlation coefficients of 0.484 and 0.485, respectively. The evening relative humidity (RH II) had a positive highly significant positive correlation coefficient of 0.664. Chitosan merits as a multiple stress tolerance enhancing agent that will further help in mitigating climate change adaptations in grapevines reducing reliance on chemical agro-inputs.

Grapevine Pinot gris virus spreads in infected vineyards: latent infections have no direct impact on grape production.

BACKGROUND: Grapevine Pinot gris virus (GPGV) infects grapevines worldwide and causes symptoms such as chlorotic mottling and deformations on leaves, stunted shoots and short panicles, or none of these symptoms if it appears as latent infection. So far, the consequences of GPGV infections for winegrowers are difficult to assess since important information such as plant performance at different GPGV infection levels and symptom expression are not fully clarified. METHODS: In order to investigate the course of GPGV spread, annual visual evaluations and ELISA tests were conducted over 3-4 consecutive years in four GPGV-infected vineyards in southern Germany: GEM, HEC, NIM, and REI. The program PATCHY was used to analyze spatial disease patterns. Sanger sequencing was used to determine virus isolates in vines at different GPGV infection levels, to test their respective influence on symptom expression. Yield and GrapeScan (FTIR) analyses were conducted to test the impact of different GPGV infection levels and isolates on fruit quantity and quality. RESULTS: GPGV infections significantly increased in all four vineyards (GEM 22-32%, HEC 50-99%, NIM 83-90%, REI 56-76%) with significant spreading patterns across and along rows. Specific symptom progression patterns were not observed. According to our results, the virus isolate has an influence on whether symptoms develop during a GPGV infection. While yield analyses revealed that yield losses only occur in symptomatic vines and range from 13 to 96% depending on the severity of symptoms, latent infections have no impact on grape production. No relevant effects of GPGV infections on must quality were observed. CONCLUSIONS: Secondary spread of GPGV was observed in all vineyards monitored, indicating vector-borne transmission that is likely to be accelerated by human viticultural management. GPGV should be further monitored to prevent the accumulation of detrimental symptomatic isolates. The results of this study can be used to assess the risk of GPGV to viticulture and should be considered when developing management strategies against the virus.

Mechanisms of grapevine resilience to a vascular disease: investigating stem radial growth, xylem development and physiological acclimation.

BACKGROUND AND AIMS: Plant vascular diseases significantly impact crop yield worldwide. Esca is a vascular disease of grapevine found globally in vineyards which causes a loss of hydraulic conductance due to the occlusion of xylem vessels by tyloses. However, the integrated response of plant radial growth and physiology in maintaining xylem integrity in grapevine expressing esca symptoms remains poorly understood. METHODS: We investigated the interplay between variation in stem diameter, xylem anatomy, plant physiological response and hydraulic traits in two widespread esca-susceptible cultivars, 'Sauvignon blanc' and 'Cabernet Sauvignon'. We used an original experimental design using naturally infected mature vines which were uprooted and transplanted into pots allowing for their study in a mini-lysimeter glasshouse phenotyping platform. KEY RESULTS: Esca significantly altered the timing and sequence of stem growth periods in both cultivars, particularly the shrinkage phase following radial expansion. Symptomatic plants had a significantly higher density of occluded vessels and lower leaf and whole-plant gas exchange. Esca-symptomatic vines showed compensation mechanisms, producing numerous small functional xylem vessels later in development suggesting a maintenance of stem vascular cambium activity. Stabilization or late recovery of whole-plant stomatal conductance coincided with new healthy shoots at the top of the plant after esca symptoms plateaued. CONCLUSIONS: Modified cropping practices, such as avoiding late-season topping, may enhance resilience in esca-symptomatic plants. These results highlight that integrating dendrometers, xylem anatomy and gas exchange provides insights into vascular pathogenesis and its effects on plant physiology.

Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis in hot conditions despite less drought-resistant leaves.

BACKGROUND AND AIMS: Many agricultural areas are expected to face hotter, drier conditions from climate change. Understanding the mechanisms that crops use to mitigate these stresses can guide breeding for more tolerant plant material. We tested relationships between traits, physiological function in hot conditions and historical climate associations to evaluate these mechanisms for winegrapes. We expected a more negative leaf osmotic potential at full hydration (πo), which reduces leaf turgor loss during drought, and either a metabolically cheaper or more osmoprotectant leaf chemical composition, to allow cultivars associated with hot, dry regions to maintain greater gas exchange in hot growing conditions. METHODS: We measured πo, gas exchange and leaf chemistry for seven commercially important winegrape cultivars that vary widely in historical climate associations. Vines were grown in common-garden field conditions in a hot wine-growing region (Davis, CA, USA) and measured over the hottest period of the growing season (July-September). KEY RESULTS: The value of πo varied significantly between cultivars, and all cultivars significantly reduced πo (osmotically adjusted) over the study period, although osmotic adjustment did not vary across cultivars. The value of πo was correlated with gas exchange and climate associations, but in the direction opposite to expected. Photosynthesis and πo were higher in the cultivars associated with hotter, less humid regions. Leaf chemical composition varied between cultivars but was not related to climate associations. CONCLUSIONS: These findings suggest that maintenance of leaf turgor is not a primary limitation on grapevine adaptation to hot or atmospherically dry growing conditions. Thus, selecting for a more negative πo or greater osmotic adjustment is not a promising strategy to develop more climate-resilient grape varieties, contrary to findings for other crops. Future work is needed to identify the mechanisms increasing photosynthesis in the cultivars associated with hot, dry regions.

Bimodal pattern of allometric scaling along grapevine shoots.

BACKGROUND AND AIMS: Each branch internode, and the organs growing on it, can be seen as a single morphological phytomer subunit, made of structurally and functionally interrelated components. However, allometric relationships between anatomy and morphology of these subunits remain unclear, particularly in the axial context. This study aims to address this knowledge gap, by measuring morpho-anatomical parameters and their allometric relationships along grapevine shoots. METHODS: To facilitate comparison, shoot length was normalized and a relative position index was calculated for each internode, ranging from 0 at the base to 1 at the apex. Scaling relationships between morpho-anatomical parameters along the axis were developed and validated by statistical modeling. KEY RESULTS: Most morpho-anatomical parameters displayed an axial behaviour of increasing then decreasing in size from base to apex, with the exception of shoot diameter and shoot vessel density. Relative position index of 0.2 acted as the data turning point for most variables analysed. During the first phase (relative position index below 0.2), the phytomer organs traits are uncoupled and show weak allometric correlation, and during the second phase the traits are strongly allometrically related. CONCLUSIONS: Our findings suggest that allometric relationships along grapevine shoots are not constant- they exhibit a bimodal pattern, possibly influenced by seasonal temperatures. This work could aid managing productivity shifts in agricultural and natural systems under global climate change and add to basic knowledge of differentiation and development of growth units in plants.