Resumen de The effect of post-veraison water deficit on yield components and maturation of irrigated Shiraz (Vitis vinifera L.) in the current and following season

Peter R. Clingeleffer, Paul R. Petrie, Nicola M. Cooley

• Given their perennial nature, grapevines can respond to deficit irrigation during both the current season as well as during the following season, even though full irrigation may have been restored during that second season. To define the cropping responses involved, three post-veraison irrigation treatments were imposed on spur, mechanically and minimally pruned Shiraz vines that were already receiving restricted water application using Partial Rootzone Drying (PRD). The treatments resulted in the vines receiving 1.25 ML per hectare pre veraison and the three irrigation treatments receiving 1.25, 0.65 and 0 ML of water per hectare in the post-veraison period. Water deficit during the current season reduced berry and bunch weight, and yield. Sugar concentration was reduced, and phenolic concentration increased when less water was applied, but anthocyanin concentration was unaffected. Although irrigation was returned to standard practice (PRD) in the following season, yield was reduced in accordance with deficit irrigation treatments the previous season. This reduction in yield was primarily caused by fewer bunches per vine, which in turn was a direct consequence of fewer shoots per vine (lower budburst). The lower crop load on the vines that had received restricted irrigation post-veraison in the previous season resulted in higher sugar and antho¬cyanin concentrations in fruit the following season. Lighter pruning resulted in a greater number of smaller bunches comprising smaller berries. In both seasons the minimal pruning treatment delayed fruit maturity as measured by sugar accumulation. Post-veraison water deficit thus has the potential to impact on both yield and fruit composition during the current season as well as during the subsequent season.