Skin phenols in seedless grapes (Vitis vinifera L.) as influenced by genotype and irrigation

Astract. Black/red grapes are rich in phenol compounds. Many clinical studies have underlined the health benefits of consuming phenol-rich foods in order to reduce the risk of developing degenerative diseases. The berry phenols accumulation has a genetic base, but, its final expression is influenced by soil, climate, grape maturity and cultural practices. A trial was run in Southern Italy to assess berry skin phenols in three seedless cultivars, at a same degree of grape maturity (sugar concentration): Black Emerald (early ripening), Autumn Royal (medium-late ripening) and Crimson Seedless (late ripening). Moreover, the seeded cv Black Pearl was included in the study as a reference. It was evident that the two cultivars with darker berry skin color (Black Emerald and Black Pearl) accumulated a higher amount of phenols per gram of fresh berry, while the cultivar with lighter (red) skin color (Crimson Seedless) performed at the opposite; the cultivar with dark blue skin color (Autumn Royal) performed intermediately. However, the difference in phenol amounts was not limited to anthocyanins, but concerned also others phenol compounds. Autumn Royal and Crimson Seedless were also tested to evaluate phenol differences in grapes produced by “normallyirrigated” and “deficit-irrigated” vines. By comparing the phenol accumulation as related to the irrigation level, a genotype-irrigation interaction was noticed: grapes from deficit-irrigated Autumn Royal vines showed a moderate decrease in berry weight but a high increase in phenol amount per kilogram of grape, while Crimson Seedless, in this trial, did not show a relevant difference of berry skin phenols related to the irrigation level.