CLIMATE CHANGE EFFECT ON POLYPHENOLS OF GRIGNOLINO GRAPES (VITIS VINIFERA L.) IN HILLY ENVIRONMENT

Abstract

Current changes of ecoclimatic indicators may cause significant variation in grapevine phenology and grape ripening. Climate change modifies several abiotic factors (e.g. temperature, sunlight radiation, water availability) during the grapevine growth cycle, having a direct impact on the phenological stages of the grapevine, modulating the metabolic profile of berries and activating the synthesis and accumulation of diverse compounds in the skin of berries, with consequences on the composition of the grapes.

The influence exerted by different meteorological conditions, during three consecutive years (2020-2022) on secondary metabolites such as the polyphenolic profile of Grignolino grapes was investigated. The samples were collected from three vineyards characterized by different microclimatic conditions mainly related to the vineyard aspect and to a different age of the plants.

Significant variations were observed in temperature and rainfall patterns among the different vintage years. The response of grape secondary metabolism to abiotic stress, with particular emphasis on polyphenolic profile of the berries was evaluated using spectrophotometry and HPLC.

The results highlighted significant differences among the vintages for each vineyard as to the berry weight and the contents of the several classes of polyphenols. 2022 Vintage distinguished by a series of extreme conditions in terms of high temperature and low rainfall, showed low berry weight and skin contents of almost all polyphenols, especially for the southwest exposed vineyards. The seeds, on the other hand, exhibited higher amounts of polyphenols, possibly due to their greater extractability. Berry weight being equal, fresh conditions during the green phase until veraison, followed by dry and hot pre harvest period privileged phenolics mainly in the berries of the southeast vineyard. Younger vineyard showed more result variability through the years.

The intensity and mainly the timing of meteorological fluctuations affected the final content in phenolics of Grignolino grapes. In hilly environment, conditions of limited water availability and high temperature, that lately are characterizing the second part of berry development, seem to support the grape quality of Grignolino, a cultivar of medium-late ripening, by limiting the differences on bunch ripening, allowing a greater accumulation of secondary metabolites, but maintaining at the same time an optimum balance sugar/acidity.