Cumulative response of Tempranillo vines subjected to the crop forcing technique to pre-forcing and post-veraison water stress on yield and grape and wine quality

Abstract

Elevated temperatures during berry ripening are detrimental to grape quality. The crop forcing technique (summer pruning that ‘forces’ the vine to start a new cycle) increases must acididy and malic acid concentration at harvest by delaying the date of veraison. However, little information is available on the sensitivity to water stress sensitivity of forced vines. A 3-year experiment was conducted to test three irrigation strategies in forced vines: a minimum threshold of mid-day stem water potential (Ψs) of -0.75 MPa before forcing (DI), minimum threshold of Ψs -1.2 MPa only after veraison (RDI) and the combination of both treatments (DI + RDI). Results were compared to a non-forced treatment with a minimum threshold of Ψs of -1.2 MPa after veraison (C-RDI). Must acidity was increased, and pH decreased in the forced treatments. However, yield was reduced by 35% and irrigation requirements increased by 20% when comparing forced and unforced treatments. As a result, water use efficiency was reduced in forced vines. Only after a dry spring, DI (11%) and DI + RDI (30%) saved water compared to C-RDI. Moreover, although punctual Ψs before forcing never fell below − 0.75 MPa, a significant negative correlation (R2 = 0.76) was found between the integral of water stress before the vines were forced and the number of forced bunches per vine. On the other hand, water stress after veraison in forced vines reduced the polyphenol content of the wine. Our fundings suggest that forced vines are extremely sensitive to even mild water stress.