The Effect of Trellis Systems on the Performance of Vitis vinif era L. cvs. Sultanina and Chenel in the Lower Orange River Region

The effect of six trellis systems on the reproductive and vegetative performance of Sultanina and Chene), grown in the lower Orange River region of South Africa, was investigated. Larger trellis systems significantly increased the yield of both cultivars, and the photosynthetic activities of the leaves at veraison as well as the canopy light environment tended to be higher for these systems. The higher yields recorded for Sultanina were attributed to improved budding percentages, which were caused by improved light environments at the basal 'buds. The improved yield obtained for Chene! however, was due to higher bunch masses, which were most likely caused by the higher photosynthetic activities of the leaves

Mitigation and Adaptation Practices to the Impact of Climate Change on Wine Grape Production, with Special Reference to the South African Context

In South Africa, environmentally and socio-economically sustainable wine grape production is promotedby governmental and private initiatives. All the initiatives contribute to establishing a scientificallybased response strategy of agro-systems to ensure sustainable production under future expected climateconditions. South African wine grape producers would probably have to cultivate their grapevines underhigher atmospheric CO2 levels and in warmer, mostly drier, conditions. Due to the projected increase inclimatic variability, an effort must be made to improve the resilience of vines against these environmentalconditions. Whole-vine functioning and balances should be considered when adjustments are madeto current long and short term cultivation practices. All practices should be aimed at promoting thedevelopment of a deep, dense and buffered root system that is able to support a well-developed canopywith optimal microclimate that would sustain a high yield of good quality. Mitigation and adaptationstrategies would most likely have to be region specific, and small scale terroir data, (which should includeboth climate and terrain/soil information) may play a critical role in decision-making

Distribution of 14C-Photosynthetate in the Shoot of Vitis vinifera L. cv Cabernet Sauvignon I. The Effect of Leaf Position and Developmental Stage of the Vine

The distribution of photosynthetates, originating in leaves of different parts of the shoot of Vi tis vinifera L. cv Cabernet Sauvignon at berry set, pea size, veraison and ripeness stages, was investigated. Specific photosynthetic activity of the "CO,-treated leaves gradually decreased during the season. Photosynthetates were hoarded in the leaves at berry set, but were increasingly diverted to the bunches after that. The apical leaves displayed the Itlghes.t.photosynthesis. The leaves opposite and below the bunches accumulated very little photosynthetafes, especially from veraison to ripeness. Redistribution of photosynthetates among the basal, middle and apical leaves was generally very restricted at all stages. Multidirectional distribution from the site of application of 14CO, occurred at berry set stage, while from pea size to ripeness photosynthetates were mainly translocated basipetally. Highest accumulation in the bunches occurred at veraison, while the basal leaves were primarily used to nourish the bunch

The Effect of Partial Defoliation, Leaf Position and Developmental Stage of the Vine on the Photosynthetic Activity of Vitis vinifera L. cv Cabernet Sauvignon

The effect of partial defoliation, :eaf position and developmental stage of the vine on the photosynthesis, stomatal resistance and transpiration of Vitis vinifera L. cv Cabernet Sauvignon was investigated. Partially defoliated vines displayed a higher rate of photosynthesis, generally increasing with degree of defoliation. The highest photosynthetic rates were found for the apical leaves, while those of the leaves opposite and below the bunches were restricted. Generally, rate of photosynthesis declined as the season progressed. The course of transpiration rate and stomata! resistance correlated with that of the rate of photosynthesis. However, transpiration and photosynthesis correlated poorly in the case of the apical leaves. In general, photon flux density and relative humidity at the leaf surface increased with an increase in defoliation percentage for all leaf positions. Leaf temperature was not significantly affected by partial defoliation. The results of the investigation suggested that excess vegetative growth is detrimental to interior-canopy microclimate as well as the photosynthetic rate of the entire vine. Partial defoliation seemed to provide a means to reduce some of the deleterious effects of vigorous growth

The Effect of Partial Defoliation, Leaf Position and Developmental Stage of the Vine on Leaf Chlorophyll Concentration in Relation to the Photosynthetic Activity and Light Intensity in the Canopy of Vitis vinif era L. cv. Cabernet Sauvignon

The effect of partial defoliation and leaf position on leaf chlorophyll concentration in relation to the photosynthetic activity and light intensity in the canopy of Vitis vinifera L. cv. Cabernet Sauvignon was investigated at berry set, pea size, veraison and ripeness stages. The leaves of the severely defoliated vines appeared to contain the highest chlorophyll concentration.In general, chlorophyll a decreased as the leaves were situated progressively deeper into the canopy. No consistent relationship between chlorophyll concentration, light intensity and photosynthetic activity could be found for the different leaf positions. However, to obtain leaves that photosynthesize optimally, the amount and time of leaf removal in the grapevine canopy must be carefully planned

Suitability of Some Climatic Parameters for Grapevine Cultivation in South Africa, with Focus on Key Physiological Processes

To optimise the functioning of the grapevine in a specific environment and to improve grape and wine quality,suitability of climatic parameters for key grapevine physiological processes needs to be assessed at fine scales. Thispaper presents methodology using hourly weather data in three wine producing regions of South Africa (CoastalRegion – Stellenbosch district; Breede River Valley – Robertson district; Central Orange River Region – Upingtondistrict) during the pre- (November to December) and post-véraison (January to February) periods. Durationsinside and outside an optimum climatic range and of extreme climatic conditions were calculated over a 5-yearperiod (1999/2000 to 2003/2004) to quantify a climatic profile related to grapevine physiological requirements.Climatic requirements for optimum photosynthetic activity were defined as follows: temperature 25°C to 30°C,windspeed <4 m/s, relative humidity 60% to 70%. Unsuitable climatic periods for vine performance werecalculated as <20°C and >35°C, >4m/s, <50% and >80%. A coefficient was assigned to each climatic parameteraccording to an assumed importance level for physiological processes. Optimum temperature requirements forother physiological parameters were also investigated. A diurnal minimum/maximum temperature range of25°C to 30°C was used for sugar content and organic acid levels and a maximum night/day temperature rangeof 15°C/25°C for colour and flavour. Light intensity was accepted as being sufficient. Stations were classifiedaccording to their potential for meeting the climatic requirements of each physiological parameter. Markedvariation in climatic profiles and available time for optimal physiological functioning occurred between regions.All factors considered, the climatic profile of the Coastal Region (Stellenbosch district) seemed to best satisfy theclimatic requirements of the physiological parameters studied

Berry Size and Qualitative Characteristics of Vitis vinifera L. cv. Syrah

The effect of variation in berry size on berry composition was studied in irrigated Syrah/R99 grapevines,located in a temperate area of South Africa. Berries from 45 clusters, sampled from both sides of the canopy(east and west), were weighed to create four categories: 1. less or equal to 1.5 g; 2. between 1.51 g and 2.00 g;3. between 2.01 g and 2.50 g; 4. more than 2.50 g. Berry physical characteristics were determined and totalanthocyanins and seed flavonoids were analysed by spectrophotometry and anthocyanin profiles by HPLC. Theratio of skin weight:berry weight did not change with increasing berry size, but the ratio of seed weight:berryweight increased. For total anthocyanins, varying results were obtained if values were expressed in mg/berry,mg/g skin, mg/kg grape and mg/cm2 skin. The quantity of total anthocyanins changed positively with increasingberry weight if expressed in mg/berry and remained almost similar if expressed in mg/cm2 of skin. In contrast,total polyphenols decreased with berry weight if the values were expressed in mg/kg grape and in mg/g skin.Total anthocyanins expressed in mg/kg grape and in mg/g skin were correlated positively to the number ofberries as well as to the total skin surface in one kilogram of grape. In this study, the largest berries seemed tohave lower quality characteristics. In order to obtain better wine quality, it seems important to reduce berryweight and, in general, berry size variability of Syrah. The obtainment and continuity of a particular wine stylemay be affected by berry variability

Shoot Heterogeneity Effects on Shiraz/Richter 99 Grapevines. I. Vegetative Growth

In this study the vegetative growth parameters of normally developed and underdeveloped shoots were compared in an attempt to quantify shoot heterogeneity in a Shiraz/Richter 99 vineyard. A field trial was performed in the Stellenbosch area,Western Cape, South Africa. Comparisons based on certain vegetative growth parameters were made between normally developed and underdeveloped shoots from both shaded and well-exposed canopies. The longer primary shoots of the normally developed shoots matured earlier in the season, with less apparent competition between shoot lignification and grape ripening. Reserves were more evenly distributed in these shoots. Total starch content over the whole shoot was found to be higher in the normally developed shoots, particularly when wellexposed. More and longer secondary shoots occurred on the normally developed shoots than on the underdeveloped shoots. No difference was found in the number of primary leaves (leaves on primary shoots) betweennormally developed and underdeveloped shoots, although the leaf area was much larger in the case of the former.  Normally developed shoots had more and larger secondary leaves (leaves on secondary shoots), while all the leaves that developed in the shaded canopies were found to be larger than those in the well-exposed canopies with a higher leaf area:mass ratio. The normally developed shoots seemed to have a greater potential for producing a higher yield, with better quality, than the underdeveloped shoots, as they have a more desirable leaf area composition in addition to a larger total leaf area per shoot

Leaf:Fruit Ratio and Vine Water Status Effects on Grenache Noir (Vitis vinifera L.) Berry Composition: Water, Sugar, Organic Acids and Cations

Seasonal variation in the water, sugar, organic acid and cation contents of developing grape berries (Vitis viniferaL. ‘Grenache noir’) under different levels of water supply (with and without deficit irrigation) and leaf:fruit ratios(18, 10 and five leaves per primary shoot, with one bunch per shoot), were investigated over two successive years inMediterranean conditions (South of France). Fourteen shoots per vine were left for each leaf:fruit ratio level, andeach vine was considered as having homogeneous primary shoots. The growth rate of the berries was increased withirrigation. Total dry matter content of the berry was not affected by leaf:fruit ratios, but the sugar loading decreasedduring berry development with a lower leaf:fruit ratio (five leaves per bunch). Treatments had little effect on organicacid contents and pH. Berry cation accumulation depended on vine water status and not on the total leaf area ofthe vine. Under irrigated conditions, calcium continued to accumulate in the berries after véraison. This confirms apartial functioning of the berry xylem during the post-véraison period. The seasonal variation in berry compositionwas less dependent on the leaf:fruit ratio than on the water status of the vine (mainly cations and sugar). This studyprovides evidence for the importance of plant water status effects on berry composition, irrespective of the leaf:fruitratio. Vine water status is a major regulating factor for source-sink relationships

The Effect of Rootstock Cultivar and Bud Load on the Colour of Vitis vinifera L. cv. Muscat noir (Red Muscadel) Grapes

The effects of rootstock cultivar and bud load on colour expression in the grapes of Vi tis vinifera L. cv. Muscat noir were investigated. Different rootstocks had no significant effect on skin colour density of the grapes Grapes from vines with a low bud load (16 buds.vine·') had the highest skin colour density