Deciphering the impacts of berry irradiation and temperature on flavonoid composition in grapevine (Vitis vinifera cv. Syrah)

Abstract

Environmental factors affect grape production by impacting carbon acquisition, source-sink relationships, berry ripening processes and the resultant wines. At the fruit level, it is generally accepted that high irradiance enhances the synthesis of anthocyanins and flavonols. On the other hand, in warm climates, high temperature experienced during early afternoon by berries exposed to direct sunlight causes large decreases in phenolic content of grape berries. The purpose of this study was to investigate the relationship between fruit composition and microclimate by collecting detailed temperature and irradiance measurements at the berry scale and measuring the corresponding phenolic composition. A field experiment was established using a split-plot design in which fruit temperature and irradiance were modified by controlling sun exposure, and by heating selected bunches by using a passive heating system (open-top system). Light interception and fruit temperature were continuously recorded from fruit-set to maturity by using light micro-sensors and thermocouples inserted into selected berries. Anthocyanin dynamics were measured during fruit development from bunch closure to maturity using an optical sensor based on auto-fluorescence. Flavonoids (flavanols, flavonols and anthocyanins) were determined at maturity. We found that total anthocyanin content was mainly driven by temperature regimes, whereas the percentage of individual anthocyanins remained stable. By contrast, flavonols were mainly affected by light regime. Finally, flavanols were not significantly affected by treatments. These preliminary analytical results, combined with high resolution microclimate recording, open the possibility to construct response-curves for a wide range of environmental conditions.