Enhancing the color traits of ‘Nebbiolo’ and ‘Dolcetto’ grapes: the role of abscisic acid during ripening

Abstract

The red Italian variety Nebbiolo (Vitis vinifera L.), used in the production of the prestigious Barolo and Barbaresco wines, is renowned for its aromatic and structural complexity but also for its low color intensity. This lack of pigmentation and the prevalence of oxidizable disubstituted anthocyanins, compounds responsible for the red color, are intrinsic characteristics of the grape variety, resulting in wines with lighter color compared to other red varieties. Firthermore, the impacts of climate change, particularly rising temperatures, are likely to exacerbate this issue by further decreasing anthocyanin concentrations. ‘Dolcetto’ grapes exibit higher anthocyanin content compared to ‘Nebbiolo’ however, they are equally susceptible to the adverse effects of heat waves. One potential solution is the application of abscisic acid (ABA), which can not only increase total anthocyanin content but also modify the anthocyanin profile towards trisubstituted forms, thereby enhancing color stability and intensity. A trial was conducted on cv. Nebbiolo and Dolcetto grapes to evaluate the effect of ABA in an experimental vineyard located in Alba, Piedmont (Italy). A 1.5 mM ABA solution was sprayed on the grape clusters at two stages: at 30% veraison and 20-25 days after this stage. Four clusters per plant received the treatments for each of four replicates. Three samplings were carried out: before ABA application, and after the first and second ABA applications. In each sampling, the weight of 100 berries, berry diameter, Brix degree, pH, total acidity, tartaric acid, malic acid, citric acid, glucose, and fructose were determined. Additionally, anthocyanin concentration and profile are being evaluated by HPLC. Whole berry and skin texture analysis was done at harvest. Data were analyzed by one-way ANOVA and Tukey test. Results showed that the treatment did not affect any variables such as berry weight, pH, Brix degree, total acidity, or texture parameters for ‘Dolcetto’. However, an increase in the anthocyanin content have been found in the treated berries compared to the control. Contrary, ‘Nebbiolo’ showed a significant increase in berry weight, Brix degree, and pH, while total acidity decreased with the treatment. Anthocyanin content in ‘Nebiolo’ is being evaluated.