2019 ASHS Annual Conference

The organoleptic properties of most fruits get great benefit from exposure to solar radiation. In wine grapes, fruit location is highly focalized under the canopy, and thus, trellising, pruning and canopy management practices aim to achieve an adequate fruit density and exposure. The accumulation of flavonols is the most universally reported acclimation response of plant tissues to UV-B radiation. In fact, flavonol synthesis is upregulated by solar radiation leaving a fingerprint on flavonol profile. Over the years, we have collected pieces of information about the factors affecting flavonol accumulation and profile. The aim was to investigate the reliability of flavonol profile as an indicator to assess the overall exposure of red wine grape berry to solar radiation. We performed three experiments to study the response of flavonol accumulation and profile to (1) three different solar radiation exclusion treatments during berry development; (2) canopy porosity and leaf area index (LAI); and (3) spatial variability of water status, vigor and ripening and cultural practices in commercial vineyards. Results showed a strong relationship between global radiation, inverse dormant pruning weights or canopy porosity (inversely proportional to LAI) and % kaempferol or % quercetin. In addition, the increase in concentration of the above two flavonols was associated with a reduction of % myricetin. Total flavonol content, % kaempferol, % quercetin and % myricetin were not consistently correlated to berry ripening or water deficit. Flavonol profile was associated to site hydrology (wetness index) through changes in vigor, and responded to shoot thinning or fruit-zone leaf removal. Other flavonoids such as anthocyanins, proanthocyanidins and flavan-3-ols were negatively correlated to % kaempferol. In addition, % kaempferol correlated to the maximum temperature of the clusters. The removal of berry 3-Isobutyl-2-methoxypyrazine, an aroma characteristic of bell peppers, was not correlated to a greater exposure. In contrast, soluble solids level were strongly related to 3-Isobutyl-2-methoxypyrazine levels. These results support the reliability of the flavonol profile as an assessment parameter for studies aiming to discuss canopy architecture or the effect of solar radiation on grape berry composition.