SATI Beyond The Bunch 2nd Quarter 2026

No fewer than 48 grapevine rootstocks are officially available in South Africa, and 28 of these are offered by nurseries. Despite all these options, nearly 95% of new vines are grafted on Ramsey, and Paulsen 1103 accounts for most of the rest (according to the most recent PlantSA figures). To provide growers with information about other rootstock options, SATI embarked on a series of rootstock trials in 2019. The SATI-funded trials were planted in two phases (in 2019 and 2022). The project is currently managed by Kebo Toolo of Provar, an independent cultivar-evaluation company, contracted to conduct the research. This work builds on the results of rootstock trials conducted by Jan Avenant while he was based at the ARC Infruitec-Nietvoorbij (he summarises those

results in Table-grape rootstocks in South Africa). However, the SATI-funded trials include new rootstocks that were not previously evaluated, and the scions represent contemporary cultivars. Phase 1 concluded in 2025 and assessed Harmony, Paulsen 1103, Ramsey, Richter 110, RS-3, RS-9, Ruggeri 140, and SO 4. They were evaluated at five sites (Begin, Buffelskraal, Denau, Vorentoe, and Yarona). Site and scion details are given in Table 1. Phase 2, which runs until 2028, includes Freedom, GRN-2, GRN-4, Kingfisher, Minotaur, Paulsen 1103, and Ramsey. Note that GRN-2, GRN-4, Kingfisher, and Minotaur are not yet officially registered in South Africa. Phase 2 is planted at three sites (JDK, Excelsior, and Yarona). Site and scion details are given in Table 2.

How are the rootstocks evaluated?

The researchers analyse this data using statistical methods, allowing them to tease apart genetic and environmental contributions to rootstock performance and assess which rootstock fares best at each site. Additionally, the evaluators are interested in each root stock’s adaptability and stability. Adaptability reflects how well a cultivar can cope with a range of environ ments, whereas stability reflects the consistency of a cultivar’s behaviour across environments and seasons.

The trials are planted in commercial vineyards, and the experimental vines are managed like commercial vines. In each phase, the same rootstocks are planted at each site, but they are grafted to a different scion at each site (Tables 1 and 2). Over the course of six years, the rootstock evaluators collect data on vegetative growth, vigour, fertility, fruit yield and quality, and other viticultural charac teristics.

KEBO TOOLO | PROVAR

BEYOND THE BUNCH • 5 • QUARTER 2 • 2026