The effect of postharvest defoliation on carbon balance of Sauvignon blanc vines

Abstract

A study was undertaken to quantify the importance of postharvest carbon assimilation on replenishment of CHO reserves of high-yielding Sauvignon blanc vines. The study mimicked the effect of a canopy-killing ‘early’ autumn frost by imposing full vine postharvest defoliation. The trial, conducted in a vigorous Sauvignon blanc vineyard in Marlborough New Zealand, was set up as a randomised block design with defoliation [Defol] or not [Fol] immediately after harvest. The treatments were carried out annually on the same vines over the whole 3-year period. Samples of root and trunk tissue were taken throughout those years for carbohydrate (CHO) analysis. CHO from Defol roots was depleted faster between harvest and dormancy than in Fol vines. Data suggest that during this period of three to four weeks, vine starch reserves are mobilised to compensate for the shortage of CHO in the trunk because of the applied treatment. Reduction of CHO did not influence grape yield or fruit composition in the first year. However, the cumulative effect over consecutive years of defoliation reduced both vegetative growth and yield. This suggests that autumn frost protection could be beneficial for vines with low carbohydrate reserves.