WINETECH Technical Yearbook 2021

When canopy densi ty increases, i t can negatively affect the grapevine microclimate. To avoid this situation, canopy managemen t ac t i ons a r e implemented to bring vines’ vegetative and fruiting performance in balance by reducing shoot length, leaf density, and number of clusters per vine. Those techniques eventually improve light in the canopy environment, a key requirement in fruit and vegetative growth. Pioneer studies have illustrated that the application of seasonal practices have a great impact on grape and wine composition (Volschenk & Hunter, 2001). For example, components such as total soluble solids increase when partial defoliation is practiced; at the same time, this practice can reduce TA in the fruit depending on the cultivar. In addition to basic oenological parameters, other components such as odour and flavour molecules are affected by alteration of the canopy environment, for example in case of compounds sensitive to light. The timing of seasonal practices is of utmost importance, as this can affect the synthesis and accumulation of certain compounds, improve grape composition, control yield, etcetera. Leaf removal can also have positive results on Botrytis incidence reduction.

When it comes to permanent structures, different trellising systems create their own micro-climatic conditions noted in differences in air movement, bunch temperature and air temperature around canopies. The conditions created can be linked to effects in the vegetative growth, grape composition, and wine composition and quality, but also water usage as trellis type can influence the transpiration. Grapevines on a horizontal trellis have higher transpiration rates than those on vertical trellises. Another benefit of trellising vines is the significant role they have on yield, although results are site and cultivar dependent. EFFECTS OF TRELLISING SYSTEMS ON SHADE AND LIGHT Canopy division promotes increases in yield and quality (Shaulis et al ., 1966), and improvement of training systems overcome canopy shading. Canopy shade is a common problem in vineyards and can cause reductions in vineyard yield and wine grape quality. In grapevine canopies, depending on architecture, foliage and fruit berries can develop in conditions varying from shaded through to fully exposed (open). In general, berries developed from open canopy conditions have higher juice sugar concentration, improved acid balance, less unripe herbaceous fruit characters and

berry phenolics concentration increases including anthocyanins in red varieties as opposed to shaded canopy conditions (Gladstones, 1992). Shaded canopies entail trellising systems such a Santorini and Stok-by-paaltjie, whereas open canopies include systems such as Ballerina and Smart Dyson (vertically divided), T-frame and Lyre (horizontally divided). EFFECT OF TRELLISING SYSTEM ON GRAPE AND MUST COMPOSITION Trellis effect on yield Trellis improves the canopy microclimate and leads to improvement in yield and quality, because of better leaf and fruit exposure to sunlight. As vine density can differ according to the planting, mass of grapes per vine is sometimes used in the scientific literature as opposed to mass per vineyard surface, more used in practice. Canopy division is an effective vehicle for accommodating high vine vigour by enhancing leaf and fruit microclimate, although results are site- and cultivar- dependent. For most of the cultivars, horizontally divided canopies have positive effects on yield as they increase shoots exposure and improve bud fruitfulness due to good sunlight penetration. Vine architecture that can support a larger canopy can ensure proper light exposure

which may produce quality grapes and therefore wines. However, this may not always be the case, as other factors may play a role. Trellis effect on grape and must composition Generally, berries maturing in densely shaded canopy interiors are generally associated with low total soluble solids, high titratable acidity, and low pH among others when compared with berries in open or exposed canopies. Solar irradiation affects the levels and pattern of sugar accumulation, organic acids, and amino acids across grape clusters; for example, increasing sunlight exposure is associated with lower accumulation of organic acids. Effect of trellising systems on wine composition Light has been shown to affect the accumulation of aroma precursors, volatile compounds, and phenol free glycosides and, as a consequence, affect the chemical and sensory properties of wine. Only few investigations have been done in the South African environment and its climate, especially on white varieties and more specifically Chenin blanc. Nevertheless, the findings of Van Zyl and Van Huyssteen (1980) demonstrated a significant effect of trellising on Chenin

WINETECH TECHNICAL YEARBOOK 2021 | 84