Institute for Wine Biotechnology

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Browsing Institute for Wine Biotechnology by browse.metadata.advisor "Carey, Victoria"

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    The effect of wind on the performance of the grapevine
    (Stellenbosch : Stellenbosch University, 2005-12) Pienaar, Jacobus Wilhelm; Carey, Victoria; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology .
    ENGLISH ABSTRACT: Wind, as a component of the environment, contributes to the viticultural concept of terroir in the South Western Cape region of South Africa. Many other components also contribute to terroir (e.g. soil, altitude, direction of slope, etc.) and it is difficult to quantify the contribution of each. A good terroir promotes slow and complete ripening of the berries. A vineyard on such a terroir produces good quality crops over time and the effects of climatic extremes on the performance of the vine are limited by this terroir. Although grapevines in the South Western Cape are exposed to strong synoptic southerly and southeasterly winds during the growing season and sea breezes add to the effect of wind in coastal areas, little is known about the effect of wind on grapevine performance. This preliminary study was undertaken to obtain more information on the effect of wind on some morphological and reproductive characteristics of Merlot nair. The aim was to obtain preliminary data which can serve as a basis for future studies on the effect of wind on grapevine performance. Important differences .in wind speed were measured spatially in a selected vineyard and exposure to wind was observed to result in essential viticultural differences. The effect of wind on vegetative parameters, canopy density, yield, berry composition and wine quality was investigated. Wind caused leaves on primary shoots of exposed vines to be smaller, but increased lateral growth in their fruiting zones. Sheltered vines had longer shoots but no significant differences were measured concerning cane diameter and pruning mass. Although it was expected that sheltered vines would have denser canopies, similar canopy densities were measured for both treatments. Vines exposed to wind responded with decreased stomatal conductance. As a result, leaf temperature was affected, showing differences between sheltered and exposed vines. Sheltered vines had more bunches per vine but fewer berries per bunch. As a result, bunches of sheltered vines were smaller than those of exposed vines. No significant difference was observed concerning the yield under the two treatments. The effect of wind on stomatal conductance had an essential impact on berry composition, thus directly influencing the quality of wine. Grapes from exposed vines showed a higher colour index. Berries from sheltered vines had significantly lower pH values and potassium concentrations and the malic acid content was lower than in berries from exposed vines. Wine from sheltered vines had more vegetative undertones in comparison with the stronger fruity character of exposed vines. A better acid balance, together with superior complexity (fullness/mouth feel), contributed to the better overall quality identified during the evaluation of wine produced from sheltered vines.