Table grape rootstocks in South Africa

INTRODUCTION R ootstocks offer producers a strategy to improve grapevine performance. Although ungrafted vines may produce acceptable yields of high quality grapes, there are risks because Vitis vinifera vines roots are sensitive to soilborne pests such as nematodes and phylloxera, as well as diseases and unfavourable soil conditions (such as low nutrient status or salinity). Using the correct rootstocks helps overcome many of these problems in the root zone. Recommending the most suitable rootstock is complicated because scion cultivar, soil type and climatic conditions differ. Consequently, each situation is unique. Research results from 27 years of evaluation, indicate performance differences between different scion cultivars on the same rootstock on the same site. Long-term trial results show that rootstock performance and the ranking of rootstock performance vary from one season to the next. Consequently, the cumulative performance of each scion and rootstock combination must be evaluated over time, to make reliable recommendations. The evaluation trials have demonstrated that a minimum of eight seasons of cumulative production evaluation results is required to provide scientifically sound recommendations. Inferior grape quality caused by excessive vigour can occur when rootstocks with inherently strong growth are combined with strongly growing scions. Therefore, rootstock evaluation trials must focus on identifying and developing rootstocks with vigour qualities that are compatible with the scion cultivar of interest to deliver economic yields of optimum quality. Rootstocks have a noticeable effect on the performance of table grape cultivars. Trials have already shown there is no universal rootstock that performs best with every scion cultivar. It is, therefore, worth noting that little or no information is available about rootstock influence on newly developed cultivars. In the rootstock evaluation trials conducted by the ARC Infruitec-Nietvoorbij in the Western and Northern Cape, rootstock performance for specific cultivars, soil types and site suitability were compared. The objectives of the trials were: • table grapes in terms of: - growth yield and quality

- provision of high yields without negatively affecting quality • to make recommendations regarding the best rootstocks for: - different soil types - specific scions, especially newly bred cultivars All trials were laid out according to the standard statistical design. In all trials, treatments (rootstocks) consisted of experimental unit sizes ranging from four to six vines per unit. Treatments were allocated randomly over the trial site in blocks and repeated five to six times. The trials, which were not performed on experimental farms, were cultivated and managed by the various participating producers. Viticultural practices applied in trial blocks were according to standard cultivation guidelines for the cultivar in the area. To explain the outcome of the trials, the following was determined: soil samples were taken to determine the pH balance, plant nutrient status and chemical properties of the soil and determine and quantify the presence of soilborne pests and diseases. The nutrient content of petioles was determined at berry set. The virus status of all scion-rootstock combinations was also determined. The names of rootstocks as used in this publication are according to the South African Varietal List for fruit crops as maintained by the Registrar of Plant Improvement of the Department of Agriculture, Forestry I n 1982, table grape research done at the FFTRI (Fruit and Food Technology Research Institute, or Infruitec) was transferred to the VORI (Viticultural and Oenological Research Institute, or Nietvoorbij). At the takeover of viticultural research by VORI, there were several rootstock trials in different phases of development at the Bellevue experimental farm, the Hex River Valley experimental farm, and several commercial farms. These trials consisted mainly of rootstock hybrids developed by Stellenbosch University (US hybrids), which were compared to and Fisheries (Anon, 2017) About the trials

10 Table Grape Rootstocks in South Africa