BUNCH EXPOSURE TO DIRECT SOLAR RADIATION INCREASES ORTHO-DIPHENOL ANTHOCYANINS IN NORTHERN ITALY CLIMATIC CONDITION

Aims: Berry anthocyanin contents were studied in eight different field experiments involving various grapevine (Vitis vinifera L.) cultivars (Syrah, Croatina, Sangiovese, Nebbiolo, Nebbiolo Rosé, Carmènere and Cannonau) in a variety of sites located in Northern Italy. Methods and results: In each experiment, global irradiance was reduced by approximately 95% by applying specially designed boxes to selected bunches before the onset of ripening. Variations in anthocyanin accumulation and profile were studied on sun exposed and shaded bunches. Exposed bunches were subjected to less favorable temperatures for biosynthetic metabolism than shaded bunches, due to frequent excessive temperatures around noon. Conclusions: Exposure to direct solar radiation induced an earlier and faster anthocyanin accumulation and a higher anthocyanin concentration across all the experiments, at least from veraison to mid ripening. In fact, the light induced elevated rate of anthocyanin accumulation did not always result in a higher anthocyanin content at grape maturity. In the cultivars with a relatively high proportion of acylated forms, sun exposure resulted in a relative increase in the quantities of non-acylated glucoside forms, while the acylation profile of cultivars that generally had a lower proportion of acylated forms was only minimally influenced by sun exposure. Significance and impact of the study: Akey observation resulting from anthocyanin profiling is the strong positive correlation between light exposure and increases in the percentage of delphinidin-, cyanidin- and petunidin-3-monoglucoside, that is, anthocyanins containing an orthodihydroxyl group.