Grapevine roots: the dark side

The rootstock modifies the arbuscular mycorrhizal community of the root system, while the influence of the scion is limited in grapevines

Understanding the effects of grapevine rootstock and scion genotypes on arbuscular mycorrhizal fungi (AMF), as well as the roles of these fungi in plant development, could provide new avenues for adapting viticulture to climate change and reducing agrochemical inputs. The root colonization of 10 rootstock/scion combinations was studied using microscopy and metabarcoding approaches and linked to plant development phenotypes. The AMF communities were analysed using 18S rRNA gene sequencing. The 28S rRNA gene was also sequenced for some combinations to evaluate whether the method changed the results. Root colonization indexes measured by microscopy were not significantly different between genotypes. Metabarcoding analyses showed an effect of the rootstock genotype on the β-diversity and the enrichment of several taxa with both target genes, as well as an effect on the Chao1 index with the 18S rRNA gene. We confirm that rootstocks recruit different AMF communities when subjected to the same pedoclimatic conditions, while the scion has little or no effect. Significant correlations were observed between AMF community composition and grapevine development, suggesting that AMF have a positive effect on plant growth. Given these results, it will be important to define consensus methods for studying the role of these beneficial micro-organisms in vineyards.

Both the scion and rootstock of grafted grapevines influence the rhizosphere and root endophyte microbiomes, but rootstocks have a greater impact

BACKGROUND

Soil microorganisms play an extensive role in the biogeochemical cycles providing the nutrients necessary for plant growth. Root-associated bacteria and fungi, originated from soil, are also known to influence host health. In response to environmental stresses, the plant roots exude specific molecules influencing the composition and functioning of the rhizospheric and root microbiomes. This response is host genotype-dependent and is affected by the soil microbiological and chemical properties. It is essential to unravel the influence of grapevine rootstock and scion genotypes on the composition of this microbiome, and to investigate this relationship with plant growth and adaptation to its environment. Here, the composition and the predicted functions of the microbiome of the root system were studied using metabarcoding on ten grapevine scion-rootstock combinations, in addition to plant growth and nutrition measurements.

RESULTS

The rootstock genotype significantly influenced the diversity and the structure of the bacterial and fungal microbiome, as well as its predicted functioning in rhizosphere and root compartments when grafted with the same scion cultivar. Based on β-diversity analyses, 1103P rootstock showed distinct bacterial and fungal communities compared to the five others (RGM, SO4, 41B, 3309 C and Nemadex). The influence of the scion genotype was more variable depending on the community and the investigated compartment. Its contribution was primarily observed on the β-diversity measured for bacteria and fungi in both root system compartments, as well as for the arbuscular mycorrhizal fungi (AMF) in the rhizosphere. Significant correlations were established between microbial variables and the plant phenotype, as well as with the plant mineral status measured in the petioles and the roots.

CONCLUSION

These results shed light on the capacity of grapevine rootstock and scion genotypes to recruit different functional communities of microorganisms, which affect host growth and adaptation to the environment. Selecting rootstocks capable of associating with positive symbiotic microorganisms is an adaptation tool that can facilitate the move towards sustainable viticulture and help cope with environmental constraints.

Towards grapevine root architectural models to adapt viticulture to drought

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

SNPs Associated with Foliar Phylloxera Tolerance in Hybrid Grape Populations Carrying Introgression from Muscadinia

Leaf-feeding phylloxera decreases the photosynthetic activity of a grape plant, leading to decreasing number of fruit buds. In addition, phylloxera larvae emerging from the leaf galls may colonize the roots, negatively affecting the growth of the grape plant. In this study, we evaluated host tolerance of three grapevine hybrid populations obtained from crossing of the same maternal grapevine M. no. 31-77-10 with interspecific hybrids carrying introgressions from Muscadinia and other North American Vitis species against leaf-feeding grape phylloxera. Combining genotyping data of the populations obtained with 12,734 SNPs and their resistance phenotypes evaluated in the laboratory experiment, we performed an association study. As the result of GWAS, nine SNPs with the lowest significant p-values were discovered in the whole sample of 139 hybrids as associated with variation of the scores ‘the percentage of infested leaves’ and ‘intensity of gall formation’. Three of the SNPs on LG 7 were located in the same chromosome interval where a major QTL (RDV6) for root phylloxera resistance was reported from Muscadine background. Two SNPs on LG 8 were detected within the gene, encoding E3 ubiquitin-protein ligase UPL4 involved in apoptosis. SNPs detected on LG 13 and LG 18 may overlap with the previously reported QTLs for phylloxera resistance inherited from V. cinerea.

Transcriptomic and biochemical investigations support the role of rootstock-scion interaction in grapevine berry quality

Background

In viticulture, rootstock genotype plays a critical role to improve scion physiology, berry quality and to adapt grapevine (Vitis vinifera L.) to different environmental conditions. This study aimed at investigating the effect of two different rootstocks (1103 Paulsen - P - and Mgt 101–14 - M) in comparison with not grafted plants - NGC - on transcriptome (RNA-seq and small RNA-seq) and chemical composition of berry skin in Pinot noir, and exploring the influence of rootstock-scion interaction on grape quality. Berry samples, collected at veraison and maturity, were investigated at transcriptional and biochemical levels to depict the impact of rootstock on berry maturation.

Results

RNA- and miRNA-seq analyses highlighted that, at veraison, the transcriptomes of the berry skin are extremely similar, while variations associated with the different rootstocks become evident at maturity, suggesting a greater diversification at transcriptional level towards the end of the ripening process. In the experimental design, resembling standard agronomic growth conditions, the vines grafted on the two different rootstocks do not show a high degree of diversity. In general, the few genes differentially expressed at veraison were linked to photosynthesis, putatively because of a ripening delay in not grafted vines, while at maturity the differentially expressed genes were mainly involved in the synthesis and transport of phenylpropanoids (e.g. flavonoids), cell wall loosening, and stress response. These results were supported by some differences in berry phenolic composition detected between grafted and not grafted plants, in particular in resveratrol derivatives accumulation.

Conclusions

Transcriptomic and biochemical data demonstrate a stronger impact of 1103 Paulsen rootstock than Mgt 101–14 or not grafted plants on ripening processes related to the secondary metabolite accumulations in berry skin tissue. Interestingly, the MYB14 gene, involved in the feedback regulation of resveratrol biosynthesis was up-regulated in 1103 Paulsen thus supporting a putative greater accumulation of stilbenes in mature berries.

Wood and roots of major grapevine cultivars and rootstocks: A comparative analysis of stilbenes by UHPLC-DAD-MS/MS and NMR

INTRODUCTION

Grapevine wood and roots are by-products obtained during vineyard management. This plentiful biomass is known to be rich in stilbenes and can be used as a source of high-value compounds as well as active natural extracts. However, the stilbenes in grapevine wood and roots from different cultivars and rootstocks remain to be characterized.

OBJECTIVE

The present study investigated the stilbene content of eight major Vitis vinifera cultivars and six different rootstocks. In addition, the distribution of stilbenes was established for each of seven parts into which the plants were sub-divided.

METHODOLOGY

For stilbene characterization and quantification purposes, an ultra-high performance liquid chromatography-diode array detector-mass spectrometry (UHPLC-DAD-MS/MS) analysis of different samples was carried out. Moreover, structural data of stilbenes was unambiguously studied by nuclear magnetic resonance (NMR) spectra.

RESULTS

Whatever the cultivar/rootstock combination, stilbenes were found to be oligomerized from the aerial part to the root system. Furthermore, stilbene content varied widely depending on the cultivars and rootstocks. For instance, the cultivars Merlot, Tannat and Gamay noir were the richest in stilbenes while the rootstocks Gravesac, Fercal and 3390C contained the highest amounts.

CONCLUSION

These findings provide insight into the knowledge that major grapevine cultivars and rootstocks can be used as a potential source of complex stilbenes.