Table grape rootstocks in South Africa

rootstocks commonly used in the table grape industry (Jacquez, Rupestris du Lot, Richter 110, Richter 99 and Ramsey). The data and conditions of all these trials were evaluated and those trials which were to be discontinued or concluded, were identified (Deist, 1997). During this period, evaluation of rootstocks for table grape vines was identified as a high priority. A new generation of rootstock trials was laid out using a split plot design. In these trials, “new” rootstocks, which had been included in wine grape trials, some US hybrids, and rootstocks being used in the table grape industry at the time, were included (Deist, 1997). One of the limitations of the “old” concept trials was that they only supplied answers to a specific scion cultivar. In the “new” rootstock trials, the split plot design allowed several scions to be compared. Researchers could obtain answers for more than one scion cultivar on various rootstocks in the same experimental block. ARC Infruitec-Nietvoorbij conducted a very successful trial of this nature at the Roodeplaat Research Station outside Pretoria (four scion cultivars grafted onto eight different rootstocks – a total of 32 scion-rootstock combinations). This was the first rootstock trial in the northern part of the summer rainfall region (Deist, 1997). Two similar trials were planted in the Western Cape, one on the Hex River Valley experimental farm (five scion cultivars grafted onto 16 different rootstocks; 80 scion rootstock combinations, and another on the Nietvoorbij experimental farm near Stellenbosch (seven scion cultivars onto 24 different rootstocks; 168 scion-rootstock combinations). In 1996, the data and vigour performance of all these trials were evaluated. Those trials that could be concluded, or had to be terminated, were identified and it was decided to end the trial at Nietvoorbij. The trial at the Hex River Valley experimental farm was continued until 2002. With the release of two new promising table grape cultivars from the ARC Infruitec-Nietvoorbij’s breeding programme in 1997, the question arose which rootstock should be used. In 1997, Regal Seedless and White Gem were established in two separate localities on the commercial farm Malanot (later La Ferme Derik)

in Agter-Paarl. Each scion cultivar was grafted onto 11 different rootstocks. For practical reasons, a single scion cultivar was included for evaluation on each of these sites. Researchers did this to simplify the viticultural management of the trial block within a commercial configuration. The first table grape trials in the Lower Orange River region were planted in 2008. The climate and soil in this area differ substantially from that of the Western Cape. The success of a suitable scion cultivar would depend on the success with which a chosen rootstock would adapt to the hardy climatic conditions in this region. Margarodes was one of the known soilborne pests which were causing severe damage in the area at that stage. Surveys before the start of these trials showed that margarodes had destroyed three of the best phylloxera resistant rootstocks (R 99, 101-14 Mgt and Rupestris du Lot) (De Klerk, 1975). New vineyards planted in the Lower Orange River region were also established on the warmer soils along the river west of Kakamas. Replanting of vineyards also took place on a large scale in the Lower Orange River region. According to Burger et al . (1972) indications were that the replanting problem occurs in drier areas and on heavier soils types under alkaline and saline conditions. With Ramsey’s establishment on soils on which this rootstock was used before, producers experienced fewer problems. However, the success rate of replanting vineyards with most other rootstocks was unknown. At that stage, it was accepted that rootstock evaluation is a long-term process and that field trials should continue for between 10 to 15 seasons before reliable recommendations could be made. In a trial on raisin grapes conducted over 18 years, 28 rootstocks with Sultanina H5 as scion were evaluated. This trial was also used to determine the minimum number of seasons necessary for scientifically acceptable recommendations to be made. This investigation has shown that reliable evaluation of rootstocks over a shorter period is possible, namely at least eight seasons of production data (Avenant, 2014). A shorter evaluation process will significantly benefit the table grape industry, mainly because new cultivars are becoming available more regularly.

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