Abstract
and SO4 rootstocks were assessed over six consecutive seasons in a factorial field trial on an Avalon soil in Stellenbosch that had been limed to pH 5.75 (1M KCl). Ruggeri 140 promoted the highest cane mass (vigour), highest petiole and must nitrogen (N), lowest ratio of yield to cane mass, and lowest overall wine quality. The lowest cane mass and highest wine quality were produced by vines on 110R. Petiole N, phosphorus (P), calcium (Ca) and magnesium (Mg), and must N and Ca, were also lower for vines on 110R than for those on 140Ru.

Research in South Africa has shown that rootstocks differ in their response to variables such as locality (Zeeman, 1978) , and to a variety of soil factors, notably acidity (Conradie, 1983) , salinity (Southey & Jooste, 1991) , form, depth, texture and water retention (Van Zyl, 1988 , and references therein). Rootstocks also differ in rooting pattern (Swanepoel & Southey, 1989 ). These differences may be reflected in various aspects of scion performance (Conradie, 1983; Archer & Fouché, 1987; Southey & Fouché, 1990; Southey & Jooste, 1991) . Information concerning the likely reactions of specific scion cultivar x rootstock combinations under given conditions is therefore necessary if vineyards are to be planned and managed effectively. This article reports on the relative characteristics of two cultivars, each on four rootstocks, assessed over post-planting seasons five to ten, inclusive.
MATERIALS AND METHODS
The trial was carried out on a colluvial, coarse sandy loam to sandy clay loam Avalon soil (Soil Classification Working Group, 1991) of mixed granite and shale derivation, on a lower midslope site at Nietvoorbij Research Farm, Stellenbosch (33˚55'02"S, 18˚51'56"E). In autumn 1988, after soil analysis, sufficient calcitic lime and phosphorus (P) were incorporated by ripping and deep ploughing to 100 cm to give an average pH of 5.90 (1M KCl) and an estimated P concentration of 30 mg.kg -1 . Four rootstocks, namely Richter 99 (99R), Richter 110 (110R), Ruggeri 140 (140Ru) and SO4, each grafted onto the scion cultivars Pinot noir and Chardonnay, were planted in factorial combination at a spacing of 2.5 x 1.0 m. Each 10-vine experimental unit (plot) was replicated in five blocks. Plots in the same row were separated by ten buffer vines. Rows containing plots were separated by at least one buffer row. Micro-sprinkler irrigation was installed, and the maturing vines were trained to a four (fixed) strand hedge trellis system. The vines were pruned to six double bearers per running metre of cordon. Nitrogen (N) was applied to the young vines at 30 kg N.ha -1 at bud break and again in November. After bearing commenced, N was applied at 15 to 20 kg.ha -1 at bud break, with a further 20kg N.ha -1 in the post-harvest period (Conradie, 1994) . The production vines also received an annual potassium (K) application in the spring at 3 kg K.ha -1 for each ton of anticipated grape production (Conradie, 1994) . Pest control sprays and other vineyard management practices were applied in accordance with conventional vineyard practice. No further action was taken until the 1992/3 season, by which time bearing was established in a consistent pattern. When sampled in the winter of 1993, the soil had an average pH of 5.75 (1M KCl), whilst the Bray II extractable P and K concentrations averaged 8.0 mg.kg -1 and 46.5 mg.kg
MATERIALS AND METHODS
respectively. Levels of exchangeable acidity, sodium (Na), K, calcium (Ca) and magnesium (Mg) were 0.0, 0.06, 0.11, 4.01 and 0.47 cmol(+).kg -1 respectively. Phosphorus was added as a single topdressing at 180 kg P.ha -1 in the spring of 2003, and dolomitic lime at 2 t.ha -1 (Conradie, 1994) . Petiole sampling was carried out at fruit set in seasons 1992/1993 to 1997/1998. Sampling, and the analysis of the petioles and soil, were performed using standard ARC Infruitec-Nietvoorbij methods in accordance with the Non-Affiliated Soil Analysis Work Committee (1990). Mid-season canopy density was determined by the point quadrat method (Smart et al., 1990; Smart & Robinson, 1991) . Grapes were harvested from each experimental unit at c. 23˚B (Pinot noir) and 21˚B (Chardonnay) in February each year. The unsettled must was analysed after pressing using methods specified by the South African Wine Laboratories Association (undated). Wines were made in the Nietvoorbij Research Cellar using a standard protocol, and sensorially assessed by a panel of 12 trained judges using a nine-point scale. Pruning (cane) mass was determined each winter. The vine performance (yield, cane mass), leaf, must and wine data were tested for normality by the Shapiro-Wilk test (Shapiro & Wilk, 1965) , and then subjected to analysis of variance by the general linear means procedure of SAS 9.1.3 (SAS Institute Inc., 2003). Student's t least significant difference (LSD) values were calculated at the 5% probability level to facilitate comparison between treatment means. Means which differed at P ≤ 0.05 were regarded as significantly different.
RESULTS AND DISCUSSION
Canopy density averaged 2.6 leaf layers and did not vary significantly between treatments (data not shown). Consequently, excessive shading was not a limiting factor. Significant cultivar x rootstock interactions did not occur. Only the main effects of cultivar and rootstock were therefore interpreted. Vine performance Average yields over the seasons 1992/1993 to 1997/1998 were 9.9% greater for Chardonnay than for Pinot noir (Table 1) , but this was not significant. Although cane masses from Chardonnay were significantly (18.0%) higher than those of Pinot noir, ratios of yield to cane mass did not differ significantly between cultivars. Rootstock had no significant effect on yield. Cane mass nevertheless increased significantly, in the sequence: 110R < SO4 < 140Ru, with R99 not differing from either SO4 or 110R. Yield to cane mass ratios did not differ significantly between 99R, 110R and SO4 (6.0:1, 5.9:1 and 5.5:1 respectively), but were appreciably lower (4.4:1) for 140R. According to Zeeman (1978) , yield increases in proportion to vigour, and the optimum yield to cane mass ratio for Chenin Blanc on 99R, 110R and other rootstocks in Paarl and Stellenbosch is ± 6:1, which is close to the ratios observed for 99R and 110R in this trial. The low yield to cane mass ratio observed for 140Ru conflicts with the report by Southey and Jooste (1991) of "a highly positive correlation between yield and cane mass". Suppression of yield in overly vigorous vines has been attributed to poor fruit set by Morton (1979) , and to low budding percentages and general unfruitfulness by Carstens et al. (1981) . If cane mass is indicative of vigour, then Chardonnay is more vigorous than Pinot noir, and 140Ru promotes more vigour than SO4, 99R and 110R. Zeeman (1978) recommended that the highest possible ratio of crop per unit pruning mass should be maintained without losing vigour or quality. If so, then on soils of the same potential as in this trial, 140Ru may need to be allotted more bearer buds than 99R, 110R and SO4 to utilise the available vigour. This possibility was not tested in the present trial because it was necessary to prune all the vines in the same way.
Petiole element concentrations
Petiole N and Ca concentrations were higher than, and P, K and Mg were within, the adequate ranges of Conradie (1994) for both cultivars and for all four rootstocks (Table 2 ). These results suggest that vine performance was not limited by the undersupply, or by low root uptake, of these elements.
Petiole element concentrations
Petiole N, P, K and Mg were unaffected by scion cultivar, but petiole Ca concentrations were higher in Chardonnay than in Pinot noir. Petiole N, P and Ca concentrations were higher in 140Ru Means in the same row and data set that are followed by the same letter do not differ at P ≤ 0.05. Adequate range (minimum-maximum) (Conradie, 1994) . Means in the same row and data set followed by the same letter do not differ at P ≤ 0.05. (2001). Means in the same row and data set followed by the same letter do not differ at P ≤ 0.05. Means in the same row and data set that are followed by the same letter do not differ at P ≤ 0.05.
Petiole element concentrations
than in the three other rootstocks tested, and petiole K was higher for SO4 than for 99R and 110R. Petiole Mg concentrations were greater for 140Ru than for SO4.
Must element concentrations
Must pH, acidity and sugar content were unaffected by scion cultivar (Table 3) . Compared to values observed by Conradie (2001) , must N concentrations were low for both scion cultivars and for all four rootstocks. This result was anomalous in view of the above-range petiole N concentrations. The concentrations of P, K, Ca and Mg in the must from all scions and rootstocks were similar to those observed by Conradie (2001) . The rootstocks had no effect on must sugar content or pH; however, 140Ru induced significantly higher must acidity than 99R, 110R and SO4.
Must element concentrations
Must from Chardonnay contained higher concentrations of Ca and Mg than must from Pinot noir. Must acidity and N were higher for 140Ru than for the other rootstocks tested, but P and K were unaffected by rootstock. Calcium concentrations in the must decreased in the sequence: 110R > SO4 > 99R (140Ru did not differ significantly from SO4), and Mg in the sequence: SO4 > 110R > 99R.
Must element concentrations
Of the rootstocks, 99R was associated with low petiole Ca, and also with the lowest must Ca and Mg concentrations. Since yields did not differ significantly between rootstocks, implying that dilution was not an important factor, the low petiole and must Ca, and low must Mg concentrations in 99R may be a characteristic of this rootstock.
Sensory effects
Aroma was more prominent in the Pinot noir than in the Chardonnay wines (Table 4) . Aroma did not differ between rootstocks. Overall quality was similar in Chardonnay and Pinot noir, but decreased for rootstocks in the sequence: 110R > SO4 > 140Ru.
Sensory effects
That the highest cane mass (vigour), lowest ratio of yield to cane mass and lowest wine quality were obtained from vines on 140Ru, whereas the lowest cane mass but highest overall wine quality were produced by cultivars on 110R, accords with the inverse relationship between vigour and wine quality found by Hepner et al. (1985) .
CONCLUSIONS
Data from a six-season field trial on a limed soil in Stellenbosch indicate that yields from Chardonnay and Pinot noir are not affected by the rootstocks 99R, 140Ru, 110R and SO4. However, the ability to promote vigour (cane mass) varies between rootstocks, and decreases in the sequence: 140Ru > SO4 > 110R. Overall wine quality is not directly linked to yield, but is inversely related to cane mass.

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