A lower rate of grape berry transpiration delays ripening and reduces flavonoid content

Abstract

Exposing berries to solar radiation improves most berry composition traits. Many of these effects have been linked to photomorphogenic mechanisms and berry temperature. However, new findings are highlighting the importance of berry transpiration in an adequate ripening. The present study was carried out with the aim of evaluating the effect of two factors that affect grape transpiration (heavy shading nets and antitranspirant) on berry ripening. An experiment was carried out with fruiting-bearing cuttings of grapevine (Vitis vinifera L. cv. Malbec), applying an antitranspirant (10% v/v dimenthene) every 15 days from veraison and heavy shading nets (polyethylene with a 75% shading factor) in a factorial design (2 by 2). Berry temperature was reduced by shading but not by the antitranspirants. The treatment with shading nets reduced the total soluble solids (TSS) and the pH, while increasing the acidity. The application of the antitranspirant reduced the fresh weight of the berry, the TSS and the pH. The reduction in TSS levels, and therefore in berry ripening, could be related to a lower grape transpiration caused by both treatments, reducing the water potential gradient between the stem and the berry necessary for the correct discharge of phloem content into the fruit. In turn, both shading and antitranspirant application reduced the anthocyanin and flavonol content of the berry. This was possibly due to the lower incidence of solar radiation on the grapes. Shading reduced the flavan-3-ol content at maturity, and the antitranspirant reduced the levels of hydroxycinnamic acids and gallic acid. In our results, two treatments reducing berry transpiration through different methods induced similar impairment of ripening affecting not only the speed of technological ripening but also the accumulation of phenolic compounds.