Table grape rootstocks in South Africa

Moderate growth may result in red and black grapes with better colour than with vigorous rootstocks. Grape quality is usually good, but berry size may be smaller than where more vigorous rootstocks are used. Berry colour manipulation practices may still be required. STEP 3: Explore different rootstocks Most table grape producers’ experience is virtually entirely limited to Ramsey. Producers tend to stick to Ramsey because this rootstock usually yields excellent production of good to excellent quality grapes with most scion cultivars and in a wide range of soils. However, Ramsey does not always perform well enough to justify the virtually exclusive use thereof. Producers should give more attention to alternative rootstocks because it is risky to have an entire industry relying on mainly only one rootstock cultivar. STEP 4: Make the final selection The final selection of rootstock depends on the scion cultivar (inherent vigour, production, berry size and berry quality potential) and characteristics of specific rootstocks. The rootstock selected should be the best to overcome the inherent shortcomings of the scion cultivar or shortcomings caused by the environment, such as extremely strong vigour, poor cluster quality, inadequate berry size and insufficient colour. It is necessary to consider the soil potential and the micro-climate of the specific site and if producers will be using overhead nets. The expected vigour of a specific scion-rootstock combination should be considered when deciding on a trellis system and vine spacing.

Photo: Jan Avenant

Reaction to plant growth regulators is excellent when strong vigour is induced. Low fertility may be encountered with some vigorously growing scion cultivars, as well as poor colouring of red and black cultivars when grown in fertile soils. Sugar levels of these cultivars may be low, and the time of ripening could be delayed. GROUP 2 Vigorous rootstocks: Paulsen 1103, US 8-7, Richter 110, Richter 99 and Ruggeri 140. Regarding growth, production and berry quality characteristics, the performance of Group 2 rootstocks is intermediate compared to Group 1 and Group 3. GROUP 3 Moderately vigorous rootstocks: SO4, Freedom and Harmony The low vigour induced in scion cultivars results in the opposite reaction to Group 1 rootstocks.

58 Table Grape Rootstocks in South Africa