Accumulation and partitioning of anthocyanins in two red grape cultivars under natural and reduced UV solar radiation

Background and Aims: Plant responses to solar radiation are difficult to quantify due to interannual weather variation and to interference by other environmental factors. This study assesses the extent of the effect of UV sunlight on the accumulation and partitioning of anthocyanins in the berry skin of two red grape cultivars. Methods and Results: Ultraviolet screening treatments, visible+UV-A and visible, applied to Bovale Grande (syn. Carignan) and Cannonau (syn. Grenache) field-grown vines, in Sardinia, Italy, promoted a significant difference in the concentration of skin anthocyanins compared with that of plants exposed to natural sunlight. Thermal units for anthocyanin accumulation, estimated with an adjusted normal heat hours model, showed a highly significant difference between cultivars. The elevated duration of high temperature (HT >35°C) in the first season reduced the concentration of skin anthocyanins, with Cannonau showing greater sensitivity. Together with the light regimes, HT >35°C induced an alteration in the composition of the anthocyanins; both natural UV-B and low flux of UV-A promoted higher acylation. Conclusions: Besides light intensity, spectral composition also influenced accumulation and partitioning of anthocyanins in berry skin. The extent of alteration differs among cultivars as the combined effect of natural UV and HT >35°C drives shifts in anthocyanins biosynthesis differently. Significance of the Study: Extending knowledge of the role played by sunlight and temperature on accumulation of berry anthocyanins may help to define management practices that foster stability of berry must colour and favour an optimal phenolic profile.