Riparia Gloire Research Articles

Drought response and recovery mechanisms of grapevine rootstocks grafted to a common Vitis vinifera scion

As grapevine production is converting into irrigated systems worldwide, understanding rootstock-scion interactions at different stages of moderate drought can help to better manage water resources and the choice of rootstock. This study compared the physio-morphological drought response and recovery of a drought-sensitive (Riparia Gloire (Vitis riparia)) and a drought-tolerant rootstock (Ramsey (Vitis champinii)) grafted with Cabernet Sauvignon (Vitis vinifera), and the self-grafted control in a pot study. Ramsey had lower root-to-shoot ratio but higher performance of the root system under drought, explained by the lower root tissue density and tip suberization and higher VviPIP2;1 aquaporin expression, and faster recovery of root hydraulic conductivity and stomatal conductance after re-watering than Riparia. Riparia maintained better water status under moderate drought by early root suberization, but it was less able to restore water uptake capacity and support scion growth and leaf gas exchange after re-watering. This study shows a suite of rootstock traits that improve scion growth in response to moderate drought. Thus, these results identify traits for breeding programs and the selection of rootstocks for sustainable management of water resources under irrigated production.

Genome assembly of the hybrid grapevine Vitis 'Chambourcin'.

'Chambourcin' is a French-American interspecific hybrid grape grown in the eastern and midwestern United States and used for making wine. Few genomic resources are available for hybrid grapevines like 'Chambourcin'. Here, we assembled the genome of 'Chambourcin' using PacBio HiFi long-read, Bionano optical map, and Illumina short-read sequencing technologies. We generated an assembly for 'Chambourcin' with 26 scaffolds, with an N50 length of 23.3 Mb and an estimated BUSCO completeness of 97.9%. We predicted 33,791 gene models and identified 16,056 common orthologs between 'Chambourcin', V. vinifera 'PN40024' 12X.v2, VCOST.v3, Shine Muscat and V. riparia Gloire. We found 1,606 plant transcription factors from 58 gene families. Finally, we identified 304,571 simple sequence repeats (up to six base pairs long). Our work provides the genome assembly, annotation and the protein and coding sequences of 'Chambourcin'. Our genome assembly is a valuable resource for genome comparisons, functional genomic analyses and genome-assisted breeding research.

Abscisic acid metabolism pathways differ between grapevine species, leaves, and roots during water deficit

Abscisic acid (ABA) metabolism is complex involving biosynthesis, conjugation, and catabolism. Differences in ABA metabolism (ABA, ABA-related metabolites, and transcripts) in response to water deficit (WD) were detected in leaves and roots of four Vitis species differing in drought tolerance: Vitis vinifera (Cabernet Sauvignon), Vitis champinii (Ramsey), Vitis riparia (Riparia Gloire), and Vitis vinifera x girdiana (SC2). Concentrations of ABA and ABA-related metabolites increased after moderate or severe WD depending on species, organ, and time. Differences in ABA, glycosylated-ABA, and ABA catabolite concentrations, as well as previously investigated related transcript abundances, revealed differences in ABA metabolism pathways among the species and organs. NCED3 was a key gene in the WD response of leaves and roots of all species. NCED3 transcript abundance and ABA concentration in drought-tolerant Ramsey increased earlier and to a greater extent than other species. These species provide informative genetic resources to study ABA metabolism and drought tolerance further.

Water deficit responses of field-grown Pinot noir mediated by rootstock genotypes in a cool climate region

Under the global warming scenario, water scarcity is expected to intensify in most grape-growing regions. The use of drought-tolerant rootstocks is considered a useful tool to mitigate the negative effects of soil water deficit on vine functioning. Differences in leaf gas exchange, plant water status, specific hydraulic conductivity in petioles (Kpetiole), xylem vessel size and vegetative vigour of field-grown Pinot noir grafted onto five rootstocks (3309C, 101-14 MGt, Kober 5BB, Riparia Gloire de Montpellier, 41B MGt) were investigated during one season under water deficit in Switzerland. The water deficit was imposed by installing waterproof and non-reflecting plastic sheets on the soil from March to harvest (September) to avoid rainfall infiltration. Rootstocks had stronger effects on vine water status than on gas exchanges. During the grape ripening stage, vines grafted onto 41B MGt and 101-14 MGt were characterised by more severe water stress as shown by the lowest values of pre-dawn leaf (Ψpd), stem water potential (Ψstem) and water stress integral (SΨ), whereas 3309C and Kober 5BB rootstocks induced milder effects. Significant differences in photosynthesis (A), stomatal conductance (gs) and transpiration (E) were only observed between vines grafted onto 41B MGt and 3309C at later stages of ripening. Changes induced by rootstocks in shoot vigour, Kpetiole and the number and size of xylem vessels in petioles and stems were correlated to differential responses of Pinot noir to water deficit. The increased vegetative vigour induced by 3309C and Kober 5BB was associated with the highest Kpetiole, xylem vessel size and a good plant water status of Pinot noir under low soil water availability. Kober 5BB induced the highest yield, probably due to the better vine water status, whereas vines grafted onto 41B MGt showed the lowest malic acid content and yeast assimilable nitrogen in berries.

Grapevine rootstock genotypes influences berry and wine phenolic composition (<i>Vitis vinifera </i> L. cv. Pinot noir)

Grapevine rootstocks can affect the nitrogen (N) status of the grafted plant due to discrepancies in their nutrient uptake and their efficiency in the allocation of assimilates. When N becomes a limiting factor, the production of phenolic compounds in grapes is enhanced as a result of a down-regulation of the flavonoid production pathway. However, it is still not fully understood if the impact of rootstocks on fruit and wine composition is mediated by their effect on the vegetative growth and N status of the scion. The main objective of the study was to test if rootstock influence on Pinot noir berry and wine phenolic composition could be related to the N status of the scion. An investigation was carried out on Pinot noir (Vitis vinifera L.) vines grafted onto six rootstocks over three vintages (2012–2014). A micro-scale fermentation technique was used to produce wines from each field replicate. Scions grafted onto SO4, a high vigour rootstock, were characterised by a 15 % higher tannin concentration in berry seed and skin compared to those grafted onto the low vigour Riparia Gloire de Montpellier, while final tannin concentration in wines depended on the rootstock. Anthocyanin concentration was higher in berries of Pinot noir grafted onto R110 compared to 125AA, which was also reflected in the wines. A Multiple Linear Regression analysis suggested that rootstock influence on berry anthocyanins was linked to the N status of scion leaves (higher Leaf NBI_R). Understanding the interaction between the N uptake efficiency of rootstocks and scion berry/wine phenolic composition will help improve the selection of suitable rootstocks that match the desired wine profile.

A Characterization of a Cool-Climate Organic Vineyard’s Microbiome

The microbiome, an influential factor affecting plant health and growth, is attracting increasing interest with respect to wine grape production. The purpose of this study was to characterize the microbiome (fungi and bacteria) of the soil, cover crop roots, and grape (Vitis spp.) roots across rootstock and depth in a cool-climate, organic vineyard. The cover crop consisted of a fescue (Festuca sp.) grass, while grape roots were sampled from New York Muscat, a cool-climate hybrid, across three root types (ungrafted, 3309C and Riparia Gloire) at three root depths (0 to 15, 15 to 30, and 30 to 50 cm). The grape root microbiome was more specialized, with fewer observed amplicon sequence variants for both bacteria (16S) and fungi (internal transcribe spacer) than found in the cover crop and the surrounding soil. Grape roots were dominated by bacterial genera Pseudomonas, Niastella, and Rhizobium; most prominent fungal genera were Plectosphaerella, Trichosporon, and Ilyonectria. Although no correlations were found between α-diversity metrics and soil parameters, Pseudaleuria relative abundance was correlated with Mn, Fe, and Na levels. Soil depth explained a small portion of bacterial but not fungal variance and taxonomic composition. Rootstock type explained a portion of both bacterial and fungal variance and taxonomic composition, substantiating the role of host plant genetics in the development of the grape root microbiome. This is the first characterization of the grape root microbiome in a cool-climate Canadian vineyard.

Prioritization of vigor QTL-associated genes for future genome-directed Vitis breeding

Vigor control in grapevine may become especially important under climate change. A better understanding of gene-phenotype relationships is required in order to exploit plant genomics for breeding purposes. This research aims to use quantitative trait loci (QTLs) for vigor identified in the progeny from a cross of Ramsey (Vitis champinii) × Riparia Gloire (V. riparia). Genes located 700 kb up and downstream from each QTL position were interrogated for functional enrichment through ShinyGO online tool, based on the gene ontology annotation of Vitis vinifera PN40024. Key biological processes like phloem and xylem development, cell cycle, response to hormones, amino acid transport, tissue development, sugar metabolism, nitrogen transport, and stress/immune responses, showed functional enrichment. Integral response to light and auxin might be required for fine molecular tuning of vegetative growth in Vitis. Fifty out of 1318 candidate genes were prioritized, reducing their amount to a manageable number of candidates for further directed breeding strategies. Highlights Plant vigor control may become especially important under climate change. Genes from various vigor-related QTLs were interrogated for functional enrichment. The analysis reduced candidate gene number based on marker proximity and functional enrichment, constituting a suitable shortcut for target-directed genome-guided breeding strategies. Three TFs are strong candidates for targeted breeding: TIF - HY5, TIF - SUS1, TIF - VOZ1 potentially enhance growth by relating light response to hormone activation, and then to photosynthesis and morphogenesis.

Root pressure-volume curve traits capture rootstock drought tolerance.

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. 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'). 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. 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.

Is foliar Cl- concentration the cause of photosynthetic decline in grapevine during mild salinity?

Moderate levels of Cl- have been associated with grapevine salt tolerance. The hypothesis to be tested in this work is: photosynthesis in grapevine is negatively correlated with foliar Cl- concentration. To further test this hypothesis, multiple mild salinity experiments on four different Vitis genotypes (Cabernet-Sauvignon, Riparia Gloire, Ramsey and SC2) were conducted and photosynthesis, ion concentrations and gene expression responses were quantified. The salt-tolerant rootstock Ramsey had greater Cl- exclusion capabilities than V. vinifera cultivars both during rooted cutting greenhouse experiments and three years of field-grafted experiments; SC2 also excluded Cl-. Differential gene expression indicated that salinity affected transcript abundance more in salt-sensitive genotypes (97.7 % of DEGs in the dataset), especially chloroplast-related transcripts. The transcript abundances of known anion transporters were determined and a family of putative B transporters was associated with the Cl- exclusion phenotype. Photosynthesis and growth were maintained in Ramsey and SC2 under mild salinity. However, photosynthesis declined in Cabernet-Sauvignon with isosmotic 20 mM salt concentrations of NaCl, KCl or NaNO3, independent of the salt type. While foliar Cl- concentrations did correlate with salt tolerance during control and NaCl conditions, it was not found to be the cause of photosynthetic decline in Vitis during mild salinity.

Cluster Thinning Does Not Improve Fruit Composition in Grapevine Red Blotch Virus-infected Vitis vinifera L.

The impact of grapevine red blotch virus (GRBV) on <i>Vitis vinifera</i> L. manifests predominantly as reductions in gas exchange, berry total soluble solids, and anthocyanins. Disease management is currently restricted by incomplete understanding of virus spread and is thus limited to vine removal. The present study investigated the potential of irrigation and cluster thinning to improve fruit quality in GRBV-infected Pinot noir vines. Two irrigation levels—grower standard and supplemental (2x grower standard)—were applied in a factorial combination with two cluster thinning levels—thinned to one cluster/shoot (at peppercorn-sized berries) and nonthinned (control)—on two different rootstocks: Riparia Gloire and 3309C. Vine growth, disease severity, and fruit composition were observed for three years to understand the potential effects of the treatments on GRBV-infected vines. Supplemental irrigation attenuated the proportion of red leaves, but thinning did not have a consistent effect. Supplemental irrigation increased yield by 16 to 23% and berry mass by 9 to 10% between rootstocks. Thinning clearly decreased yield, but it also increased berry mass by 4 to 11% between rootstocks. Supplemental irrigation increased gas exchange in 2020, yet thinning slightly reduced gas exchange. These impacts on gas exchange did not affect total soluble solids in the fruit at harvest. Increases in berry sugar content indicate that sugar import increased commensurately with berry size as a function of both increased irrigation and cluster thinning. Crop load (Ravaz index) exhibited a correlation with berry sugar for the Riparia Gloire rootstock only, suggesting that crop load adjustment has a limited impact on ripening for GRBV-infected vines. Neither irrigation nor thinning significantly impacted anthocyanin concentration, and the impact on other secondary metabolites was inconsistent. The respective increase or decrease in yield may determine whether the limited improvements of supplemental irrigation and thinning on fruit quality in GRBV-infected vines are beneficial.

The relative susceptibility of grapevine rootstocks to black foot disease is dependent on inoculum pressure

Black foot disease of grapevines is a major economic issue for the viticulture industry worldwide. The disease is mainly associated with a complex of pathogen species within the genera Dactylonectria and Ilyonectria. The susceptibility of six grapevine rootstock cultivars to black foot disease under field conditions was assessed. Callused rootstocks of 101-14, 5C, 420A, Riparia Gloire, Schwarzmann and 3309C were planted into soil containing low natural pathogen populations or inoculated with isolates representing the species diversity in New Zealand. Disease incidence, disease severity and dry weight accumulation were assessed after 8 months of growth. Root and shoot dry weights were not significantly affected by inoculation treatment, but differed among rootstock cultivars, with cultivar 420A having the lowest root and shoot dry weight, cultivar 3309C having the largest shoot dry weight and cultivar 5C the largest root dry weight. The relative susceptibility of rootstocks differed significantly depending on whether they were grown under low natural inoculum pressure or a higher pressure in artificially inoculated soil. Schwarzmann and Riparia Gloire rootstock cultivars were the least susceptible under natural low inoculum pressure, but were the most susceptible in inoculated soil. In contrast, 5C was one of the most susceptible under low inoculum levels but was the least susceptible under high pathogen pressure. The result of the study indicate that black foot pathogen inoculum levels in soil affect the relative susceptibility of grapevine rootstocks to infection, and may have implications for the selection of rootstocks for planting.

Rootstocks Impact Yield, Fruit Composition, Nutrient Deficiencies, and Winter Survival of Hybrid Cultivars in Eastern Canada

Grafting cold-hardy hybrid grapevines may influence their attributes under different pedoclimatic conditions and may also contribute to cold-hardiness, influence plant physiology, and affect yield and fruit composition. In a six-year study, we evaluated bud survival, plant development, nutrient deficiencies, yield, and fruit composition for three cold-hardy grape varieties: Frontenac, Frontenac blanc, and Marquette. The grape varieties were grafted on four rootstocks: 3309C, SO4, Riparia Gloire, and 101-14. The final combinations were own-rooted. The six-year research period indicated that cold-hardy hybrids were affected differently by each rootstock. Magnesium deficiency was lower for grafted Frontenac and Frontenac blanc compared with own-rooted vines, but bud survival and grapevine development were not affected by rootstock. Moreover, results related to yield components showed that there are significant differences between rootstocks and own-rooted vines. Frontenac was the least affected grape variety compared to Frontenac blanc and Marquette, where only cluster weight and berry weight were impacted. Overall, for the two Frontenac varietals, we also observed a greater maturity for fruits of vines grafted on 101-14 and 3309C compared with own-rooted vines. Grafting affected fruit composition for Marquette differently, where the lowest grape maturity was observed for fruits on vines grafted on SO4. This study demonstrates that rootstocks affect cold-hardy hybrids, highlighting their potential under eastern North American conditions.

Nitrate Uptake and Transport Properties of Two Grapevine Rootstocks With Varying Vigor.

In viticulture, rootstocks are essential to cope with edaphic constraints. They can also be used to modulate scion growth and development to help improve berry yield and quality. The rootstock contribution to scion growth is not fully understood. Since nitrogen (N) is a significant driver of grapevine growth, rootstock properties associated with N uptake and transport may play a key role in the growth potential of grafted grapevines. We evaluated N uptake and transport in a potted system using two grapevines rootstocks [Riparia Gloire (RG) and 1103 Paulsen (1103P)] grafted to Pinot noir (Pommard clone) scion. Combining results of nitrate induction and steady-state experiments at two N availability levels, we observed different responses in the uptake and utilization of N between the two rootstocks. The low vigor rootstock (RG) exhibited greater nitrate uptake capacity and nitrate assimilation in roots after nitrate resupply than the more vigorous 1103P rootstock. This behavior may be attributed to a greater root carbohydrate status observed in RG for both experiments. However, 1103P demonstrated a higher N translocation rate to shoots regardless of N availability. These distinct rootstock behaviors resulted in significant differences in biomass allocation between roots and shoots under N-limited conditions, although the overall vine biomass was not different. Under sufficient N supply, differences between rootstocks decreased but 1103P stored more N in roots, which may benefit growth in subsequent growing seasons. Overall, greater transpiration of vines grafted to 1103P rootstock causing higher N translocation to shoots could partially explain its known growth-promoting effect to scions under low and high N availability, whereas the low vigor typically conferred to scions by RG may result from the combination of lower N translocation to shoots and a greater allocation of biomass toward roots when N is low.

Clone and Rootstock Interactions Influence the Cold Hardiness of Vitis vinifera cvs. Riesling and Sauvignon blanc

Cold damage is a threat to grapegrowers worldwide. Cold hardiness varies across Vitis vinifera cultivars, but the influence of clone and rootstock selection on this trait is unclear. Five clone x rootstock combinations of Riesling (clone 49 x Riparia Gloire (RG); 49 x SO4 Teleki; clone 239 x RG; 239 x SO4; 239 x Couderc 3309) and four clones of Sauvignon blanc (clone 242, 297, 376, and 530 on SO4 Teleki rootstock) were evaluated over three dormant seasons (2016/17, 2017/18, and 2018/19). Bud cold hardiness was quantified every two to four weeks by differential thermal analysis (DTA) and reported as low temperature exotherms (LTE). Yield and pruning weights were recorded every year. Rootstock did not consistently influence the cold hardiness of Riesling buds, although clone 239 was generally hardier than clone 49. Significant clone*rootstock interactions were observed more frequently in the first year of the study. No consistent differences were observed between Sauvignon blanc clones, although clone 242 and 297 were often amongst the least hardy clones. Differences in hardiness were not consistently related to yield, pruning weight or crop load in the prior growing season. This study demonstrates the importance of both clone and rootstock selection in cool climate regions where freeze injury may occur. Future research should consider the clone identity and the possibility of a clone x rootstock interaction when comparing the cold hardiness of different cultivars.

Modeling vegetative vigour in grapevine: unraveling underlying mechanisms

Mechanistic modeling constitutes a powerful tool to unravel complex biological phenomena. This study describes the construction of a mechanistic, dynamic model for grapevine plant growth and canopy biomass (vigor). To parametrize and validate the model, the progeny from a cross of Ramsey (Vitis champinii) × Riparia Gloire (V. riparia) was evaluated. Plants with different vigor were grown in a greenhouse during the summer of 2014 and 2015. One set of plants was grafted with Cabernet Sauvignon. Shoot growth rate (b), leaf area (LA), dry biomass, whole plant and root specific hydraulic conductance (kH and Lpr), stomatal conductance (gs), and water potential (Ψ) were measured. Partitioning indices and specific leaf area (SLA) were calculated. The model includes an empirical fit of a purported seasonal pattern of bioactive GAs based on published seasonal evolutionary levels and reference values. The model provided a good fit of the experimental data, with R = 0.85. Simulation of single trait variations defined the individual effect of each variable on vigor determination. The model predicts, with acceptable accuracy, the vigor of a young plant through the measurement of Lpr and SLA. The model also permits further understanding of the functional traits that govern vigor, and, ultimately, could be considered useful for growers, breeders and those studying climate change.

Drought tolerance of the grapevine, Vitis champinii cv. Ramsey, is associated with higher photosynthesis and greater transcriptomic responsiveness of abscisic acid biosynthesis and signaling

BackgroundGrapevine is an economically important crop for which yield and berry quality is strongly affected by climate change. Large variations in drought tolerance exist across Vitis species. Some of these species are used as rootstock to enhance abiotic and biotic stress tolerance. In this study, we investigated the physiological and transcriptomic responses to water deficit of four different genotypes that differ in drought tolerance: Ramsey (Vitis champinii), Riparia Gloire (Vitis riparia), Cabernet Sauvignon (Vitis vinifera), and SC2 (Vitis vinifera x Vitis girdiana).ResultsRamsey was particularly more drought tolerant than the other three genotypes. Ramsey maintained a higher stomatal conductance and photosynthesis at equivalent levels of moderate water deficit. We identified specific and common transcriptomic responses shared among the four different Vitis species using RNA sequencing analysis. A weighted gene co-expression analysis identified a water deficit core gene set with the ABA biosynthesis and signaling genes, NCED3, RD29B and ABI1 as potential hub genes. The transcript abundance of many abscisic acid metabolism and signaling genes was strongly increased by water deficit along with genes associated with lipid metabolism, galactinol synthases and MIP family proteins. This response occurred at smaller water deficits in Ramsey and with higher transcript abundance than the other genotypes. A number of aquaporin genes displayed differential and unique responses to water deficit in Ramsey leaves. Genes involved in cysteine biosynthesis and metabolism were constitutively higher in the roots of Ramsey; thus, linking the gene expression of a known factor that influences ABA biosynthesis to this genotype’s increased NCED3 transcript abundance.ConclusionThe drought tolerant Ramsey maintained higher photosynthesis at equivalent water deficit than the three other grapevine genotypes. Ramsey was more responsive to water deficit; its transcriptome responded at smaller water deficits, whereas the other genotypes did not respond until more severe water deficits were reached. There was a common core gene network responding to water deficit for all genotypes that included ABA metabolism and signaling. The gene clusters and sub-networks identified in this work represent interesting gene lists to explore and to better understand drought tolerance molecular mechanisms.

Potential impacts of the ring nematode, Mesocriconema xenoplax, on grapevines in British Columbia: a microplot study.

The Okanagan Valley of British Columbia hosts a wine grape industry that has grown substantially in the past three decades in terms of both acreage and economic benefit to the region. The ring nematode, Mesocriconema xenoplax, has recently been found to be widespread in vineyard soils in the region. This study used field microplots to assess the potential impacts of a local population of M. xenoplax on the first four years growth of either self-rooted ‘Merlot’ or ‘Merlot’ vines grafted onto three commonly used rootstocks: 3309C, 44-53M, and Riparia Gloire. The population of M. xenoplax multiplied to comparable levels on self-rooted vines and all rootstocks, indicating that none of the vine genotypes were resistant to M. xenoplax. Inoculation with M. xenoplax reduced cumulative pruning weights of self-rooted vines by 58%. Inoculation with M. xenoplax reduced trunk cross-sectional areas of 3309C by 45% and that of self-rooted vines by 38%, whereas it did not affect trunk cross-sectional areas of 44-53 or Riparia Gloire, indicating differing levels of rootstock tolerance to M. xenoplax. Our data suggest that M. xenoplax is likely impacting vineyard health and productivity in the region, and the selection of rootstocks and management practices to minimize impacts of this nematode should be considered in future vineyard replant management programs.

Does Inoculation with Arbuscular Mycorrhizal Fungi Reduce Trunk Disease in Grapevine Rootstocks?

Ilyonectria is a weak pathogen known for causing black foot disease in young vines, infecting roots and vascular tissues at the basal end of the rootstock and restricting the movement of water and nutrients. This negatively impacts vine establishment during transplant into the vineyard. Arbuscular mycorrhizal (AM) fungi are symbiotic fungi that associate with most plants and have been shown to mitigate the infection and effect of pathogens. This greenhouse study was designed to determine if the mycorrhizal fungi could mitigate Ilyonectria infection and whether this was dependent on inoculation timing. ‘Riparia gloire’ grapevine rootstocks (Vitis riparia) were infected with Ilyonectria either after AM fungi, at the same time as AM fungi, or to roots that were not inoculated by AM fungi. We measured the abundance using specific markers for both the pathogen and AM fungi. Colonization by AM fungi did not suppress Ilyonectria, but instead increased the abundance of Ilyonectria. Further, mycorrhizal rootstocks did not have enhanced growth effects on physiological parameters when compared to non-mycorrhizal rootstocks. These findings stand in contrast to the general perception that AM fungi provide protection against root pathogens.

Grapevine rootstocks differentially regulate root growth and architecture in response to nitrogen availability

Regulation of root system growth and architecture is an adaptive mechanism evolved by plants to cope with variable nitrogen availability in the soil. In grafted plants, this process depends on intrinsic properties of the rootstock as well as long-distance signaling between each partner of the graft (scion and rootstock) and contributes to the fitness of the whole plant. We show here that two grapevine rootstock genotypes known to differentially control scion growth have developed two distinct root development strategies to optimize nutrient uptake in response to nitrogen availability. The rootstock '1103 Paulsen' conferring high vigor developed a deeper root system and a larger number of lateral roots than 'Riparia Gloire de Montpellier' (RGM), a rootstock that confers low vigor, whatever the nitrogen concentration in the culture medium. RGM cuttings grew surface roots and developed lateral roots only with low nitrogen supply. This developmental pattern suggests that RGM promotes lateral root production when nitrogen content is limiting to increase its prospecting area for the uptake of nitrogen resources. Gene expression profiling revealed interesting patterns and differences between the two studied rootstocks, particularly concerning hormone signaling.

In vitro storage of micropropagated grapevine rootstocks at low temperature

A long-term in vitro conservation protocol for five micropropagated grapevine rootstocks (3309 Couderc, 110 Richter, Vitis riparia Gloire de Montpellier, 101-14 Millardet et De Grasset, and Teleki 5C) was developed and optimized by testing the effect of culture containers (polyethylene bags versus glass test tubes), explant types (rooted versus unrooted cuttings), low-temperature regimes (1.6, 4.0, and 7.2°C), and light intensity (low versus dark). Optimal storage conditions were achieved at 4.0°C and low light intensity (3 μmol m−2 s−1), with rooted plantlets established on woody plant medium (WPM) supplemented with 15 g L−1 sucrose and 37 mg L−1 cysteine in polyethylene bags. After 12 and 24 mo of optimal cold storage, the plant condition ratings (3.5 and 2.5 on a scale of 4) and survival rates (75% and 52%) were high, regardless of the rootstock genotype, as determined by visual observations and viability assays of subcultures on WPM supplemented with 15 g L−1 sucrose and 37 mg L−1 cysteine at 25°C, high light intensity (33 to 45 μmol m−2 s−1), and 16-h photoperiod. Prolonged storage at 4°C under low light intensity reduced the number of subcultures by 4- to 8-fold over 12 to 24 mo, which substantially lowered costs and labor, and provided opportunities for long-term germplasm conservation. Additionally, the use of polyethylene bags reduced storage space in the growth room and in a microprocessor temperature-controlled refrigerator, and also facilitated the safe exchange of germplasm across regulatory boundaries.