Effect of leaf removal on grape and wine composition in ‘Merlot’

Abstract

The adaptation to climate change requires the adjustments of viticultural practices, particularly changing the fruit to leaf area ratio which could be an effective option to maintain and enhance fruit and wine quality. Fruiting capacity and berry composition of grapevine are dependent on canopy area, with grapevine carbohydrate reserves affected by the crop load. 'Merlot' grapevines grown in the experimental vineyard of the NWGIC (South Eastern Australia) received treatments that altered the leaf area/fruit ratio. These received severe summer pruning (SSP), upper (ULR) and lower leaf removal (LLR) implemented at pea size during two growing seasons. Generally, all treatments lowered total soluble sugars, but the total sugar yield was not altered, also the total anthocyanins and phenolics of the berries did not differ at harvest. The titratable acidity and alcohol concentration of the wine was influenced by the change of the canopy size as were sensory attributes. Particularly, wines made from grapes of the SSP treatment were different in most attributes compared to wines that were made from grapes of untreated vines. The overall response of partial defoliation and severe summer pruning conducted prior to veraison suggests that it can be used as a management practise to alter berry ripening speed and grape composition, consequentially influencing wine attributes. However, depending on position, intensity and time the impact of such treatments on carbohydrate reserves in the perennial structure may have long-term implications.