Impact of temperature and solar radiation on grape composition variability in the Saint-Emilion winegrowing area 

Grape composition is strongly influenced by climate conditions. Their expected modifications in near future, notably because of increased temperatures, could significantly modify the biochemical composition of berries at harvest, and thus wine typicity and quality. Elevated temperatures favor sugar accumulation in grapes, enhance malic acid degradation and modify the amino acid content. They also reduce significantly anthocyanin accumulation in Merlot,leading to the imbalance between anthocyanins and sugars, while no significant effects on final anthocyanin levels were reported in Tempranillo^[1] and finally affect aromas or aroma precursors. However, at local scale, several other environmental factors also contribute to the overall berry composition variability between nearby vineyards and the impact of each individual factor is difficult to identify. In this context, the objective of our study was to clarify the effect of temperature variability across a network of vineyards from the Saint-Emilion and Pomerol wine producing areas, by selecting well-characterized Merlot plots presenting significant temperature differences and gradients at various time scales linked to environmental factors^[2].

The selected sites were characterized by similar soils, vine age and training system. The average temperature difference during the ripening period was about 2°C between the coldest and warmest sites. Samples of 20 to 50 berries were collected at different phenological stages from véraison to maturity in 2019 and 2020. In order to further investigate the putative impact of cluster exposure to solar radiation, the biochemical composition of berries in clusters from each side of differently oriented rows (E/W or N/S) was evaluated separately and combined with RNA-seq technology to screen differentially expressed genes at the transcriptome level.

Results showed significant effects on grape composition and gene expression profiles in relation with temperature, site, and bunch azimuth, with a noteworthy impact of temperature and solar radiation exposure on anthocyanin content in grape skins.

Acknowledgements: this project was supported by “Conseil Interprofessionnel des Vins de Bordeaux “ (CIVB) n°51640/18008/9/10

References :

1. Arrizabalaga-Arriazu, M. et al, (2020). High temperature and elevated CO₂ modify berry composition of different clones of grapevine (Vitis vinifera L.) cv. Tempranillo, Front. Plant Sci. dec 2020, 11:603687. doi: 10.3389/fpls.2020.603687
2. de Rességuier L et al (2020). Temperature variability at local scale in the Bordeaux area. Relations with environmental factors and impact on vine phenology. Front Plant Sci. may 20,11:515. doi: 10.3389/fpls.2020.00515