A comparative study on training systems and vine density in Santorini Island: Physiological, microclimate, yield and quality attributes

The Mediterranean basin is regarded as one of the most affected global regions by climate change. Traditionally, viticulture in this region copes with high temperatures, heat waves and drought. Such extreme conditions are expected to intensify due to climate change in the future. Our study focuses on the viticulture of Santorini Island, located in South Aegean (Greece). Local varieties trained with the traditional 'Kouloura' training system have been cultivated for thousands of years on the island, producing recognised high-quality PDO wines worldwide. The literature on these traditional training systems is scarce, and their investigation could aid in the adaptation of viticulture to hotter and drier future climatic conditions. The objective of this study was to compare the physiological and agronomic response of Assyrtiko grapevines to the traditional training systems 'Kouloura' and VSP training system over two growing seasons and to establish the factors influencing the performance of each system in the semi-arid conditions of Santorini Island. In brief, the 'Kouloura' training system maintained a less-stressed water status compared to VSP, while for both studied years during 'Kouloura' exhibited significantly higher photosynthetic rates and stomatal conductance. Regarding microclimate observations, we found that, especially during heatwaves, VSP's grapes were more exposed to higher temperatures during midday than 'Kouloura' and that the 'Kouloura' system protected against damage from heatwaves and strong winds when compared to VSP. Investigating the mechanisms by which these traditional training systems are adapted to hot, dry climatic conditions creates applicable knowledge for developing and using alternative training systems in similar environments to adapt to climate change.