WINETECH Technical Yearbook 2020

context of ibMP expressions, especially as the pre-véraison temperatures seem to be increasing in warmer areas where Cabernet Sauvignon plantings are prolific. The study showed the medium-vigour sites ensured sufficient light in the canopy, allowing respectable tons per hectare and more favourable sensory attributes. Moderate climates with moderate water constraints seemed to produce more complex wines than extreme climates, but it can be emphasised that effective in-season management of canopy and irrigation will ensure consistency and complexity in wines. CONCLUSION The study confirmed the hypothesis that grapevine will respond to climate change and continue to do so in the expression of phenology, growth and ripening, as the grapevine’s performance is affected by the constant environmental parameters despite the differences on vineyard and site level. Season variability was prominent in driving grapevine response, the variability compelled by extreme, out-of-the-ordinary climate events. Seasonal variability may be counteracted by viticultural practices, such as supplementary irrigation to induce or allow moderate water constraints, ensuring a more balanced grapevine in the selection of trellis system, pruning and canopy management. In the context

related to the coumaroyl derivatives; while cooler sites, seasons and higher vigour levels (shaded fruits) showed more glucosides and acetylglucoside derivatives. Season and water constraints were isolated as the primary driving factors affecting the sensory attributes of Cabernet Sauvignon. The cooler and lower water constraint sites, such as the high-vigour areas, were strongly associated with herbaceous and vegetable attributes. The warmer sites and areas of medium to low vigour were more associated with black fruit and prune attributes, as well as tasting sweeter. Methoxypyrazine (ibMP) expression was driven by temperature and water constraints over sites and seasons. The summer rainfall in one season (2013/14) hampered the degradation of ibMP due to increased vegetative growth. Seasons with warmer pre-véraison temperatures (like in 2014/15), showed to be favourable for ibMP synthesis. Shorter seasons did not allow for the effective degradation. Overall the expression seemed to be more prominent in the warmer climates, as the cooler climates had cooler pre-véraison temperatures resulting in less synthesis of ibMP. The kinetics of ibMP degradation also seemed to be slower at the sites with higher percentage of course sand and silt content. This study gave some insights into the management and planting distribution of Cabernet Sauvignon in the

by temperature and water constraints, more balanced vines were attained with moderate water constraints and moderate to warm climatic conditions. Ripening: Moderate to high water constraints ensure the canopy fills out to have sufficient balance of vegetative and reproductive growth to allow for a good tempo of sugar and anthocyanin accumulation. The balance in the grapevine therefore could drive sugar accumulation or lack thereof and indirectly affect anthocyanin accumulation due to the co-regulation nature of the compounds. Unbalanced grapevines will either not complete sugar loading before harvest is attained, or the opposite, where the sugar accumulation could stop (“gets stuck”), hampering the phenolic development of the berry. Warmer temperatures can be buffered with low to moderate water constraints. Wine: Climate was positively correlated with wine colour, as the total colour pigments and phenolics increased over the three growing seasons in relation to the increase in seasonal growing degree days. The results suggested that anthocyanin biosynthesis was more sensitive to atmospheric conditions than to water constraints under the given study conditions over sites. Season was the overriding factor affecting the anthocyanin profile, with the warmer seasons and sites being more closely

over a diverse climatic band for seven seasons, this included commercial sites and a variety of cultivars. Confirming the results from this four-year study, the phenological variability is more likely to be dictated by between-season variability rather than variability between localities. Figure 2 is a spatial image of the observed hours at 30-35°C for the 2017/18 summer ripening months (November to March), darker areas highlighting a warmer summer, therefore the areas where earlier flowering can be expected in the next season, 2018/19. The lighter areas highlight later flowering. These maps are based on observed hours at specific temperature ranges to aid management decisions. Series of hourly maps and seasonal summary maps are available at www.terraclim.co.za. CLIMATE X GRAPEVINE GROWTH, RIPENING AND WINE EXPRESSION Growth: Warmer temperatures had a positive correlation with growth early in the season and negative correlations later in the season. Shoot growth tempo was significantly slower for grapevines at the cooler site compared to the warmer sites. Vigour also had an effect on the tempo of growth and final shoot length, with the low and medium vigour having had a faster tempo of growth, but shorter shoots compared to the high vigour plots. The final shoot length attained seemed to be driven

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