Long-term observations in Napa Valley and Bordeaux reveal that grapevines never reach a lethal level of drought.

<p style="text-align: justify;"><strong>Aims</strong>: Genetic variability in grapevine cultivars may influence their strategy to cope with drought through stomatal regulation of transpiration rate. The aim of the present study was to evaluate the stomatal sensitivity of five cultivars (Ekigaïna, Grenache, Marselan, Mourvèdre, and Syrah) to soil water status and air water vapor pressure deficit (VPD).</p><p style="text-align: justify;"><strong>Methods and results</strong>: Leaf gas exchange and canopy light interception efficiency (ε_i) were evaluated through a wide range of predawn leaf water potential (Ψ_PD) measurements in a field experiment in Southern France. Additionally, greenhouse experiments were carried out to monitor stomatal response to increasing VPD levels. Ekigaïna showed a strong isohydric behavior with the highest decrease in leaf gas exchange in response to soil water stress and VPD. Mourvèdre and Grenache showed a similar but relatively less extreme behavior. These three cultivars showed a constant leaf water status during the day through stomatal regulation and a strong decrease in ε_i. In contrast, Syrah and Marselan displayed anisohydric behavior as they presented a less sensitive stomatal control. Both cultivars showed fluctuating midday leaf water potential and Marselan was the least affected in terms of ε_i.</p><p style="text-align: justify;"><strong>Conclusion</strong>: This study demonstrated that grape cultivars differed in their stomatal response to soil water deficit and VPD. For a given cultivar, a similar stomatal behavior was found in response to both Ψ_PD and VPD.</p><p style="text-align: justify;"><strong>Significance and impact of the results</strong>: Adaptation to drought and viticulture viability in hot and dry environments could be achieved by identifying and breeding cultivars with drought tolerance traits.</p>

Understanding the distribution of gas exchange within a plant is a prerequisite for scaling up from leaves to canopies. We evaluated whether leaf traits were reliable predictors of the effects of leaf ageing and leaf irradiance on leaf photosynthetic capacity (Vcmax, Jmax) in field-grown vines (Vitis vinifera L). Simultaneously, we measured gas exchange, leaf mass per area (LMA) and nitrogen content (Nm) of leaves at different positions within the canopy and at different phenological stages. Daily mean leaf irradiance cumulated over 10 d (PPFD10) was obtained by 3D modelling of the canopy structure. Nm decreased over the season in parallel to leaf ageing while LMA was mainly affected by leaf position. PPFD10 explained 66, 28 and 73% of the variation of LMA, Nm and nitrogen content per area (Na), respectively. Nitrogen content per unit area (Na = LMA ¥ Nm) was the best predictor of the intra-canopy variability of leaf photosynthetic capacity. Finally, we developed a classical photosynthesis-stomatal conductance submodel and by introducing Na as an input, the model accurately simulated the daily pattern of gas exchange for leaves at different positions in the canopy and at different phenological stages during the season.

UMR AGAP Equipe Diversité, adaptation et amélioration de la vigne (DAAV)Background and Aims: Based on 19 nuclear simple sequence repeat markers and parental analysis, we aimed to identify and propose the pedigree of different accessions held at the Estación Experimental Agropecuaria Mendoza of the Instituto Nacional de Tecnología Agropecuaria germplasmcollection. The results were compared with data recorded in large, international databases.Methods and Results: We identified 37 different cultivars, of which 18 were original and not previously identified. The parentage analysis showed that European cultivars, such as Muscat of Alexandria, Muscat à Petits Grains, Listán Prieto, Mollar Cano and Malbec, were involved in natural crossings resulting in different South American cultivars.Conclusions: Many of the cultivars identified here represent unique individuals based on their genotype. The number of cultivars that participated as progenitors in the origin of South American germplasm is higher than previously thought.Significance of the Study: Germplasm collections planted many years ago play a key role in the conservation and characterisation of genotypes that otherwise may have been lost. It is highly probable that there might be other genotypes not identified and mixed in old vineyards. The identification, rescue and conservation of these genotypes are a challenge to preserve the existing genetic variability