Tempranillo clones differ in the response of berry sugar and anthocyanin accumulation to elevated temperature.

The intra-varietal genetic diversity of grapevine (Vitis vinifera L.) may be exploited to maintain grape quality under future warm conditions, which may alter grape berry development and composition. The present study assesses the effects of elevated temperature on the development of berry, grape composition and anthocyanins:sugars ratio of thirteen clones of V. vinifera. cv. Tempranillo that differed in length of the ripening period (time from veraison to berry total soluble solids, mainly sugars, of ca. 22 °Brix). Two temperature regimes (24 °C/14 °C or 28 °C/18 °C, day/night) were imposed to grapevine fruit-bearing cuttings from fruit set to maturity under greenhouse-controlled conditions. Elevated temperature hastened berry development, with a greater influence before the onset of ripening, and reduced anthocyanin concentration, colour intensity and titratable acidity. The clones significantly differed in the number of days that elapsed between fruit set and maturity. At the same concentration of total soluble solids, the anthocyanin concentration was lower at 28 °C/18 °C than 24 °C/14 °C, indicating a decoupling effect of elevated temperature during berry ripening. Thermal decoupling was explained by changes in the relative rate of response of anthocyanin and sugar build-up, rather than delayed onset of anthocyanin accumulation. Clones differed in the degree of thermal decoupling, but it was directly associated with differences neither in the length of their ripening period nor in plant vigour.