Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Because of long-term climate changes, apparently associated with higher temperatures and fewer rainfall events, factors such as water-use efficiency and site selection for new cultivars are a matter of increasing importance for viticulture. Within this context, the root system is expected to play a key role. Its relevance to grapevine functioning is due to the numerous functions in which it is involved. In the light of this, the development of the root system is highly relevant to the viticulturist because of the fact that grapevine growth and functioning are dependent on the development of the root system. Differences can, therefore, be expected in terms of berry ripening on single grapevines of the same scion for situations with differing development of root systems, despite being grafted on the same rootstock. Root growth is influenced by several factors, among the ecological aspects. Soil parameters have a predominant influence on root growth and distribution but also annual root production can be altered by canopy manipulation. Due to the importance of root growth to the aboveground development of the vine, it is critical to gain understanding of the relationship between soil factors and root growth and distribution, and the central role that the subterranean environment plays in the concept of terroir. This study aimed to investigate the effect of selected soil physical and chemical parameters on root growth and distribution and to investigate whether having very different canopies influences root growth. In order to achieve these goals, two experiments were conducted; the first was performed in two commercial Sauvignon blanc vineyards each grafted onto Richter 110, non-irrigated, with two treatments: undisturbed lateral growth and complete lateral removal. The second study included the analysis of eight commercial Sauvignon blanc vineyards grafted onto Richter 99 and Richter 110 located in the Stellenbosch Wine of Origin District. Measurements of physical and chemical soil parameters, root growth and distribution, canopy growth and functioning, vine water status and berry composition were performed. The edaphic factors appeared to be one of the most important parameters that affected root development by changing soil water availability and possibly causing physical or chemical limitations on root growth. From the results of this study, it is clear that severe water stress and a pH (KCl) lower than 4.5 play a key role in the limitation of root growth. Due to the fact that most of the soils from the Stellenbosch Wine of Origin District, especially the subsoils, are acidic, this is a factor to consider before planting. On the other hand, the combination of favourable edaphic conditions, such as a subsoil pH of higher than 5.0, light- to mediumtextured subsoil and moderate water stress, allow increased growth of thin roots. However, the effect of canopy management on root growth cannot be discounted due to its importance in the variation of carbohydrate demand by competing sinks. This study showed that lateral removal done from when the berries are at pea size results in an increase in the number of thin roots (0.5-2.0 mm). The secondary leaf area represents at least the same leaf area as the primary leaf area in all the vineyards evaluated, which reveals the relative importance of the laterals in the total leaf area of the vine and the potential importance in terms of microclimate and leaf area available for photosynthesis. Studies of root growth should take the vineyard canopy architecture into account. / AFRIKAANSE OPSOMMING: As gevolg van langtermyn klimaatsveranderinge wat toegeskryf kan word aan die voorkoms van hoër temperature en laer reënval, is faktore soos effektiwiteit van waterverbruik en liggingseleksie vir nuwe kultivars van kardinale belang vir wingerdkunde. Binne hierdie konteks, speel die wortelsisteem ‘n belangrike rol. Die belangrikheid hiervan vir wingerdfunksionering kan toegeskryf word aan die talle funksies waarby dit betrokke is. Die ontwikkeling van die wortelsisteem is dus hoogs relevant vir die wingerdkundige, omdat wingerdgroei en funksionering afhanklik is van die ontwikkeling van die wortelsisteem. Verskille kan daarom dus verwag word in terme van korrelrypwording op ‘n enkele wingerdstok van dieselfde onderstok vir gevalle met verskillende ontwikkeling van die wortelsisteem, ten spyte daarvan dat dit op dieselfde onderstok geënt is. Wortelgroei word, onder ekologiese aspekte, deur verskillende faktore beïnvloed. Grondfaktore het meerendeels ‘n predominante invloed op wortelgroei en -verspreiding, terwyl jaarlikse wortelproduksie deur lowermanipulasie beïnvloed kan word. Weens die belangrikheid van wortelgroei vir die bogrondse ontwikkeling van die wingerd, is dit krities om kennis op te doen oor die verhouding tussen grondfaktore en wortelgroei en –verspreiding, asook die sentrale rol wat die subterreinomgewing op die terroir-konsep speel. Die studie was daarop gemik om die invloed van geselekteerde fisiese en chemiese parameters van grond op wortelgroei en -verspreiding vas te stel, en ook te ondersoek of verskillende lowers wortelgroei sal beïnvloed. Om laasgenoemde doelwitte te bereik, is twee eksperimente uitgevoer. Die eerste is uitgevoer in ‘n kommersïele Sauvignon blanc-wingerd wat geënt is op Richter 110, sonder besproeïng en met twee behandelings, naamlik onversteurde sêkondere lootgroei en volledige sêkondere lootverwydering. Die tweede studie het die analise van agt kommersïele Sauvignon blancwingerde geënt op Richter 99 en Richter 110 in die Stellenbosch Wyn van Oorsprong Distrik. Metings van fisiese en chemiese grondfaktore, wortelgroei en -verspreiding, lowergroei en -funksionering, plantwaterstatus en korrelsamestelling is uitgevoer. Dit blyk dat edafiese faktore een van die belangrikste parameters is wat wortelontwikkeling beïnvloed deur beskikbaarheid van grondwater te verander, en wat moontlik fisiese en chemiese beperkings op wortelgroei kan veroorsaak. Uit die resultate van die studie is dit duidelik dat intense waterspanning en ‘n pH (KCl) laer as 4.5 ‘n belangrike rol in die beperking van wortelgroei speel. Aangesien die meeste van die grondsoorte in die Stellenbosch Wyn van Oorsprong Distrik, veral al die subgronde, suur is, is dit ‘n faktor wat in oorweging geneem moet word voor aanplantings. Die kombinasie van gunstige edafiese toestande, soos ‘n subgrond met ‘n pH hoër as 5.0, ‘n lig tot medium tekstuur en matige waterspanning, sal dus aanleiding gee tot ‘n toename in die groei van dun wortels. Die effek van lowerbestuur op wortelgroei kan egter nie buite rekening gelaat word nie weens die belangrikheid daarvan in die variasie van koolhidraataanvraag deur kompeterende vraagpunte. Hierdie studie toon dat, indien sêkondere lootverwydering tydens ertjiekorrelgrootte toegepas is, dit aanleiding gee tot ‘n toename in die dun wortels (0.5 tot 2.0 mm). Die sêkondere blaaroppervlakte verteenwoordig minstens dieselfde blaaroppervlakte as die primêre blaaroppervlakte in al die wingerde wat ondersoek is, wat dui op die belangrikheid van sêkondere lote in die totale blaaroppervlakte van die wingerd en die potensiële belangrikheid daarvan in terme van mikroklimaat en blaaroppervlakte wat vir fotosintese beskikbaar is. Studies van wortelgroei moet lowerargitektuur in ag neem.