Philippe Vivin

Ecophysiological, Genetic, and Molecular Causes of Variation in Grape Berry Weight and Composition: A Review

Berry fresh weight and composition are under the control of complex interactions among genotype, environmental factors, and viticulture practice, which all affect not only the mean value but also the ranges of variation in berry traits. Both mean values and variation range in berry composition play a role in berry quality and, subsequently, wine typicity. This review examines recent ecophysiological, genetic, and molecular knowledge to provide better understanding of the mechanisms that influence variability in berry weight and composition. We specifically reviewed the variation range in berry weight and composition (including sugars, organic acids, and anthocyanins) among Vitis genotypes, the environmental and viticulture practices that cause variability for a given cultivar, the genetic clues underlying the genotypic variation, and the putative genes controlling berry weight and composition. Despite numerous studies comparing differences in the mean value of a berry trait among different environment conditions and viticulture practices, very few studies have explored the level of variation in response to those factors. Present genetic and molecular studies are mainly focused on identifying genes involved in the control of berry weight and composition, with few considerations of environmental factors that affect their expression. In the future, more effort should be directed toward integration of genetic and molecular work with ecophysiological approaches in an effort to gain novel insights into the cause of variability in grape fresh weight and composition.

Comparison of Three Operational Tools for the Assessment of Vine Water Status: Stem Water Potential, Carbon Isotope Discrimination Measured on Grape Sugar and Water Balance

Yield, grape composition and wine sensory attributes tightly depend on vine water status. Hence, the measurement of vine water uptake is important for research purposes as well as for practical vineyard management. Many techniques have been developed over the past decades. Among them, three are of particular interest, because they are easy to implement, robust and because their utilization is complementary: stem water potential , carbon isotope discrimination measured on grape sugar and water balance. The present chapter describes and compares these three methods . It also indicates in which situation each of them will be most useful for researchers and vineyard managers.

A 3-D functional–structural grapevine model that couples the dynamics of water transport with leaf gas exchange

Background and Aims Predicting both plant water status and leaf gas exchange under various environmental conditions is essential for anticipating the effects of climate change on plant growth and productivity. This study developed a functional-structural grapevine model which combines a mechanistic understanding of stomatal function and photosynthesis at the leaf level (i.e. extended Farqhuhar-von Caemmerer-Berry model) and the dynamics of water transport from soil to individual leaves (i.e. Tardieu-Davies model). Methods The model included novel features that account for the effects of xylem embolism (fPLC) on leaf hydraulic conductance and residual stomatal conductance (g0), variable root and leaf hydraulic conductance, and the microclimate of individual organs. The model was calibrated with detailed datasets of leaf photosynthesis, leaf water potential, xylem sap abscisic acid (ABA) concentration and hourly whole-plant transpiration observed within a soil drying period, and validated with independent datasets of whole-plant transpiration under both well-watered and water-stressed conditions. Key Results The model well captured the effects of radiation, temperature, CO2 and vapour pressure deficit on leaf photosynthesis, transpiration, stomatal conductance and leaf water potential, and correctly reproduced the diurnal pattern and decline of water flux within the soil drying period. In silico analyses revealed that decreases in g0 with increasing fPLC were essential to avoid unrealistic drops in leaf water potential under severe water stress. Additionally, by varying the hydraulic conductance along the pathway (e.g. root and leaves) and changing the sensitivity of stomatal conductance to ABA and leaf water potential, the model can produce different water use behaviours (i.e. iso- and anisohydric). Conclusions The robust performance of this model allows for modelling climate effects from individual plants to fields, and for modelling plants with complex, non-homogenous canopies. In addition, the model provides a basis for future modelling efforts aimed at describing the physiology and growth of individual organs in relation to water status.

Root transcriptomic responses of grafted grapevines to heterogeneous nitrogen availability depend on rootstock genotype

Grafted grapevines showed common and rootstock-genotype-specific root transcriptome responses under different nitrogen regimes. Functional categories and potential hub genes involved in genotype-dependent responses were identified.

Dissecting the rootstock control of scion transpiration using model-assisted analyses in grapevine

How rootstocks contribute to the control of scion transpiration under drought is poorly understood. We investigated the role of root characteristics, hydraulic conductance and chemical signals (abscisic acid, ABA) in the response of stomatal conductance (gs) and transpiration (E) to drought in Cabernet Sauvignon (Vitis vinifera) grafted onto drought-sensitive (Vitis riparia) and drought-tolerant (Vitis berlandieri × Vitis rupestris 110R) rootstocks. All combinations showed a concomitant reduction in gs and E, and an increase in xylem sap ABA concentration during the drought cycle. Cabernet Sauvignon grafted onto 110R exhibited higher gs and E under well-watered and moderate water deficit, but all combinations converged as water deficit increased. These results were integrated into three permutations of a whole-plant transpiration model that couples both chemical (i.e., ABA) and hydraulic signals in the modelling of stomatal control. Model comparisons revealed that both hydraulic and chemical signals were important for rootstock-specific stomatal regulation. Moreover, model parameter comparison and sensitivity analysis highlighted two major parameters differentiating the rootstocks: (i) ABA biosynthetic activity and (ii) the hydraulic conductance between the rhizosphere and soil-root interface determined by root system architecture. These differences in root architecture, specifically a higher root length area in 110R, likely explain its higher E and gs observed at low and moderate water deficit.

Combining ecophysiological models and genetic analysis: a promising way to dissect complex adaptive traits in grapevine

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

Phosphorus acquisition efficiency and phosphorus remobilization mediate genotype-specific differences in shoot phosphorus content in grapevine

Crop productivity is limited by phosphorus (P) and this will probably increase in the future. Rootstocks offer a means to increase the sustainability and nutrient efficiency of agriculture. It is known that rootstocks alter petiole P concentrations in grapevine. The objective of this work was to determine which functional processes are involved in genotype-specific differences in scion P content by quantifying P uptake, P remobilization from the reserves in the cutting and P allocation within the plant in three grapevine genotypes. Cuttings of two American rootstocks and one European scion variety were grown in sand and irrigated with a nutrient solution containing either high P (0.6 mM) or low P (0 mM). The high P solution was labelled with 32P throughout the experiment. The grapevine genotypes studied show variation in the inhibition of shoot and root biomass in response to low P supply, and P supply also affected shoot, but not root, P concentrations. Genotype-specific differences in total P content were related to differences in P acquisition and utilization efficiencies (PAE and PUE, respectively). Phosphorus allocation within the plant was not affected by genotype or P supply. The rootstock genotype known to confer high petiole P content in the vineyard was associated with a high PAE under high P, and a high PUE under low P. This suggests that the petiole P concentrations in the vineyard are related to genotype-specific differences in PAE and PUE, and that these traits could be used for rootstock selection programmes in the future.

Modelling grape growth in relation to whole-plant carbon and water fluxes

This study developed and used an advanced whole-plant grapevine model to unravel factors affecting water and carbon fluxes during fleshy fruit growth.

Potential contribution of strigolactones in regulating scion growth and branching in grafted grapevine in response to nitrogen availability

Grapevine rootstocks regulate scion growth and architecture differently in response to nitrogen availability. Strigolactones are suggested as key root-derived molecules modulating scion development in grafted grapevine.