Vigour control in grapevines for wine production : the effects of root restriction on the vegetative growth, fruitfulness and fruit maturity of Vitis vinifera cv. Cabernet Sauvignon

Abstract

An hypothesis that root restriction bags affect the vegetative growth, fruitfulness and fruit maturity of minimally managed field grown grapevines (Vilis vinifera cv. Cabemet Sauvignon) was examined with data collected from 1991-1996 as part of an ongoing trial. Root restriction clearly reduced vegetative growth, however fruitfulness was less affected, resulting in improvements in crop load and the maturity of the grape berries. The proportionate bag volume effects on growth were less consistent.

Grapevine cuttings were planted at ground level in porous geotextile Duon® root control bags in the spring of 1989 in Canterbury, New Zealand. Treatments consisted of four bag volumes of 10, 25, 48 and 102 litres, 'bagged' and unrestricted 'control' vines. The grapevines were spaced at 2 metre between vines and trained to a single cordon. The vines were minimally managed with winter short spur pruning and irrigation was applied uniformly across all treatments. The experiment was divided into three sections to test two hypotheses. Firstly were the bagged vines different from the non bagged vines and secondly were the bag effects proportionate.

Root restriction treatments generally reduced all vegetative growth parameters including: pruning fresh weights; trunk cross sectional area; primary and lateral shoot number and length, node number (leaf number), internode length and leaf area per plant. Mean leaf size was smaller and despite the growth reductions the canopy density was improved in the bagged vines, through less leaf shading. Root restriction affected fruitfulness to a lesser extent, leading to increased harvest efficiency indices; fruit weight per unit pruning weight, leaf area per unit pruning weight and the fruit weight produced per total shoot number. Moreover, root restriction treatments affected the main fruit maturity parameters used for wine production. At harvest root restriction treatments increased the juice total soluble solids concentrations and decreased the titratable acidity concentration leading to an increased total soluble solids to titratable acidity ratio. In the final year these differences occurred from 7 weeks prior to harvest. Root restriction treatments also decreased juice potassium ion concentration. Potassium ion concentration was correlated with pH, and pH was generally lower in the bagged vines. Berry colour development at veraison was also earlier in the root restriction treatments.

The hypothesis that bag volumes are proportionate to changes in vegetative growth, fruitfulness and fruit maturity is not clear. There was some evidence to suggest relationships between these parameters may exist, however, R2 values were low. Clearly the smallest bag volumes had disproportionate growth suggesting root escapes and, or, changed root to shoot relationships which would confound results. Root escapes were confirmed by preliminary root excavation.