Winegrowers of New Zealand represents the viticultural research and technical interests of the Wine Institute of New Zealand and NZ Grape Growers Council. Reports on the research programme of 1994/95 are now available. One programme of particular interest to Winepress readers is the work carried out on rootstock and clonal evaluation by Peter Wood, Brent Fisher and Jeff Sinnott. The full report runs to 10 pages so we have decided to print the executive summary, the discussion on clones and rootstocks and the conclusion. The full report is available from MGGA secretary, Stephanie Hagen.

Executive Summary

Winegrowers of New Zealand contracted HortResearch to conduct research to evaluate the performance of a range of Chardonnay clones, and the performance of a range of rootstocks grafted with Chardonnay, in the Poverty Bay region. This report summarises the results from the 1993, 1994, and 1995 vintages.

Eleven clones of Chardonnay, grafted on Couderc 3309, were included in the clonal trial. In 1993, 1994, and 1995, measurements taken included yield, cluster number, percentage bunch rot, berry weight, and fruit quality (soluble solids, titratable acidity, and pH of the juice). Further, in 1994 and 1995 wines were made from selected clones using a dedicated microvinification unit.

The main results were:

1. Rual proved to be the overall best performing clone. It produced the second highest yield, with the fruit attaining a good level of soluble solids at over 23 °Brix. In addition Rual showed the second lowest level of bunch rot infection.
2. Clone, 2/23 also performed very well. In common with Rual this clone had been heat treated to eliminate viruses.
3. As expected UCD4 and UCD5 produced high yields (although not much more than Rual and 2/23), but with significantly lower fruit maturity (21.1-21.7 °Brix).
4. Selections made by MAF in the 1980s from McWilliams vineyards produced moderate yields which have a high soluble solids content (23.6 °Brix).
5. Lowest yielding clones in this trial were Mendoza, UCD6, UCD15, ex Gordon, and ex Kumeu. Fruit from most of these attained a high level of soluble solids except Mendoza and UCD15 which both only reached 22.5 °Brix.
6. Five clones were selected for winemaking in 1994. A tasting of the resulting wines established the following order of preference - Mendoza (most preferred), 2/23, Rual UCD6 and UCD4. The wine made from UCD4 was significantly inferior to that from the other clones.

Twelve rootstocks were included in the rootstock trial. The scion used was Chardonnay, clone UCD6 (TK06058). In 1993, 1994, and 1995, measurements taken included yield, cluster number, percentage bunch rot, berry weight, and fruit quality (soluble solids, titratable acidity, and pH of the juice). The weight of winter prunings was determined in 1995 only. No wines were made from the rootstock trial.

The main results were:

1. Differences in vine performance which could be attributed to the rootstock were small.
2. The yields produced by most of the clones were very similar, however the overall range was 12.5 to 16.5 tonnes per hectare.
3. SO4 and Schwarzmann were the highest yielding rootstocks in this trial. Similar results were obtained in earlier MAF rootstock trials which were also carried out in Poverty Bay and utilised Chardonnay as scion.
4. There does not appear to be any relationships between the fruit quality parameters measured in the trial and the yield data obtained. However, some rootstocks did appear to be able to produce higher yields without any reduction in sugar levels.
5. In general, the higher vigour rootstock (1202, 5BB, Richter 99 & 110, Ruggeri 140, Paulsen 1103) produced lower yields, and had higher levels of bunch rot due to excessive vegetative growth. These are indications that high vigour rootstocks produce high pH juices.

Discussion

Two clones (ex Gordan and ex Kumeu) clearly produced yields worse than those experienced with the low yielding Mendoza clone. These particular clones had not been through the clonal selection process but were included because there was anecdotal evidence that they had performed well in the past. Apart from the high soluble solids levels that these two clones attained in this trial there appears to be little else to recommend them. The clone ex Kumeu has also been shown to be infected with Grapevine Leafroll virus so this may have contributed towards its poor performance.

The clone McWilliams 113 produced moderate yields of fruit at one of the lowest levels of ripeness. This clone performed quite badly in the earlier clonal selection trials and was only included as a check on the selection process.

The low yields produced by the Mondoza clone came as no surprise but the comparatively low soluble solids and high total acid were more unexpected. This clone is known to be infected - commitment needs to be made to change, and to select suitable alternatives. More immediate is the need to consider factors in relation to efficacy and cost, the two main criteria that determine the use of soft fungicides. However, when considered in conjunction with the use of conventional pesticides in an integrated disease management programme, it provides a more acceptable and cost viable option.