The effect of post-harvest defoliation on carbon resources of high yielding Sauvignon blanc grapevines

Abstract

We wanted to quantify the importance of post-harvest carbohydrate assimilation to replenish vine reserves, additional to maintaining optimal growth, productivity and fruit quality of high yielding vigorous Sauvignon blanc grapevines. To mimic the effect of autumn frost, vines were defoliated immediately after harvest. To impose additional stress on the vines the defoliation treatments was overlaid with a high crop-load treatment for which 48 and 72 nodes were retained on vertical shoot positioned (VSP) vines. For defoliation, immediately after fruit harvest, all the leaves of the vines were removed, compared to foliated vines that went through normal senescence. From just after ecto-dormancy in 2008, samples of root and trunk tissue were taken throughout the years for carbohydrate (CHO) analyses, and results compared with annual yield data. Depleted winter reserves in trunk and root were replenished during the next growth cycle, suggesting that grapevine CHO partitioning favours survival of the permanent structure over increasing vine size and/or yield. However, after two consecutive years of defoliation, the cumulative effects of smaller, less fruitful canes from year 1 and reduced carbohydrates from the subsequent year, did reduce both yield and vegetative growth in the third growing season. The results suggest that even the short-lived post-harvest canopy in cool climates contributes to the vine CHO economy. Defoliation due to autumn frost, and/or excessive crop loads affected carbohydrate reserves in vines but only after a few consecutive years of low recharge was this manifested.