Influence of Scott Henry and Four-Cane Vertical Shoot Positioning Training Systems and Crop Load on Whole- Vine Gas Exchange of Vitis vinifera L. Sauvignon blanc

Background and goals Despite the importance of photosynthesis in determining yield and fruit composition, few reports have described how photosynthesis is affected by vine management. Our objective was to understand the influence of leaf exposure and yield on whole vine gas exchange using four-cane vertical shoot positioning (VSP) and Scott Henry (SH) training systems. Methods and key findings Vitis vinifera L. Sauvignon blanc vines were managed using either four-cane VSP (all shoots upward) or SH training, in which shoots from the lower cane were trained downward, giving a greater exposed leaf area. To investigate the influence of yield, fruit was removed from one of the lower and upper canes at verasion. Training had no effect on photosynthesis in the initial 24 hours following treatment. However, the rates of SH-trained vines increased by 23 and 40% after 33 and 100 days, respectively, when compared to VSP. The rate of photosynthesis per unit leaf area was similar for both treatments. Removal of half (season one), or all the crop (season two) had no effect on photosynthesis. Training had no effect on fruit composition at harvest and fruit removal (in season one) resulted in higher soluble solids. Conclusions and significance The greater leaf area of SH-trained vines resulted in higher vine photosynthesis in the morning and afternoon, but had little effect at solar noon. Training had no significant effect on fruit soluble solids or yield but did increase trunk non-structural carbohydrate concentrations. Reducing yield had no effect on photosynthesis but increased the fruit soluble solids and trunk non-structural carbohydrate concentrations. Increasing carbohydrate reserves may improve vine productivity in future seasons.