SATI Beyond The Bunch 2nd Quarter 2026

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SATI Research Booklet

Quarter 2

BEYOND

KEBO TOOLO | PROVAR

2 0 2 6

FOCUS ON: Rootstock Trials

KEBO TOOLO | PROVAR

Rootstock evaluator Kebo Toolo (left) of Provar manages the SATI-funded trials.

BEYOND

A SATI PUBLICATION

About Beyond the Bunch This quarterly publication aims to serve as a science-based resource for the South African table-grape industry. Each edition explores a topic or questions raised by industry, with links to related additional reading. Submit your topic or questions Producers and industry stakeholders are encouraged to suggest scientific or technical questions or topics of interest. We will strive to address as many of these as possible.

Email tarryn@satgi.co.za to submit your request.

Content disclaimer SATI does not take responsibility for

accuracy or validity of information supplied by advertisers. Views expressed are those of the partner and may not reflect our organisation’s views. Contact denene@satgi.co.za to feature your brand.

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AN UPDATE ON SATI ROOTSTOCK TRIALS

Ramsey is not the only option available to table-grape growers. How does the performance of other rootstocks compare with it?

BY ANNA MOUTON

BEYOND THE BUNCH • 4 • QUARTER 2 • 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.

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BEYOND THE BUNCH • 5 • QUARTER 2 • 2026

The key takeaways

Phase 1 Figure 1 shows the cane masses of the rootstocks for those sites where there were significant differences between rootstocks. Cane mass is a proxy for vigour. It can be seen that Ramsey had above-average vigour at all sites. In contrast, SO 4 had variable vigour. Therefore, Ramsey is more stable for this trait than SO 4. Harmony was the most vigorous at two of the four sites (Vorentoe and Yarona) but it lacked Ramsey's consistency across the span of the trial. This suggests that Harmony's performance is strongly influenced by its environment.

Figure 2 shows yield differences for all sites combined, as well as for sites where there were significant differences between rootstocks. Here, both Ramsey and SO 4 were consistently high-yielding. On the other hand, Richter 110, while performing well in general, had low yields at Yarona. This suggests that Richter 110 is less stable for this trait than Ramsey or SO 4. SO 4 stood out as the most stable rootstock for high yield production across sites and seasons.

Figure 1. Cane mass in kg for the rootstocks at the sites where they differed significantly. Left to right: lowest to highest.

Figure 2. Yields in kg for the rootstocks overall and at the sites where they differed significantly. Left to right: lowest to highest.

BEYOND THE BUNCH • 6 • QUARTER 2 • 2026

However, Ramsey can be too vigorous, especially when paired with a vigorous scion. Should growers prefer a less vigorous rootstock, they can consider SO 4, as it provides similar yields to Ramsey. But their results will depend on their site, as SO 4 can equal Ramsey in vigour under some conditions.

Growers need to take site-specific performance and broader adaptability and stability into account when choosing a rootstock. For example, Ramsey is adaptable, producing high yields in different regions and on a range of soils. This makes it a safe choice, even though it might be outperformed at some sites by rootstocks that are better suited to those particular conditions.

Table 1. Site and trial characteristics for phase 1 (2019–2025). Begin Buffelskraal Denau

Vorentoe

Yarona

Vredendal Olifants River

De Doorns Hex River

Saron Berg River

Kanoneiland Orange River

Location

Scion cultivar Vine spacing

IFG 68-175 2.7 x 2.0 m

Sugrasixteen

Crimson Seedless

Sugrathirtyfive

Thompson Seedless

3.5 x 1.6 m

3.0 x 1.8 m

3.0 x 2.0 m

3.3 x 1.6 m

0–30 cm

Fine sandy loam Fine sandy loam

Loamy fine sand

Black sandy soil

Loamy fine sand Fine sandy loam Calcareous with white lime and high pH. Micro-sprinklers

30–60 cm Loamy fine sand

Fine sandy loam Alluvial soils. High salinity but optimal pH. Ridged.

Loamy fine sand Loamy fine sand

Soil

Saline with high pH.

Optimal pH.

Leached sand. Optimal pH. Wet conditions.

General

Irrigation system Drip

Drip

Trellis system

Gable

Gable with nets

Gable

The results of phase 1 are summarised in Tables 3 to 5. The tables show traits that differed significantly between rootstocks overall and at each site. If a trait doesn’t appear in a table, it didn’t differ significantly between rootstocks. In the tables, rootstocks are compared to Ramsey, based on their average performance across all years of phase 1. When considering all the sites combined, the rootstocks showed significant differences in earliness,

yield, bunch and berry mass, and sugar:acid ratio (TSS:TTA). Their relative performance is illustrated in Figures 3 to 5. Note that the letters below the rootstock names indicate statistical difference. For example, in Figure 3, RS-3, RS-9, and Ramsey do not differ significantly in earliness, as indicated by each having the letter a below their names. RS-3 is significantly earlier than SO 4 (and the rootstocks listed to the right of SO 4, none of which have the letter a below their names).

Figure 3. The bud-break earliness of the rootstocks averaged across all sites. Left to right: earliest to latest.

Figure 4. The yields of the rootstocks averaged across all sites. Left to right: lowest to highest yielding..

BEYOND THE BUNCH • 7 • QUARTER 2 • 2026

The berry masses of the rootstocks averaged across all sites. Left to right: lowest to highest berry mass.

Figure 5. The bunch masses of the rootstocks averaged across all sites. Left to right: lowest to highest bunch mass.

Figure 6. TSS:TTA of the rootstocks averaged across all sites. Left to right: lowest to highest.

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Rootstock trials are established and managed similarly to commercial vineyards.

BEYOND THE BUNCH • 8 • QUARTER 2 • 2026

Based on overall performance, Ramsey is a good option for rapid vineyard establishment. It has strong vegetative growth and adapts well to a range of environments. SO 4 also merits consideration, given its high, stable yields and consistent reproductive performance.

When considering performance across all sites, the top yielding rootstocks were Paulsen 1103, Ramsey, Richter 110, and SO 4. Of these, Ramsey and SO 4 had the heaviest bunches and largest berries.

Table 1. General and growth traits of rootstocks in Phase 1. Ramsey is the control. Rootstock Yields 1 Vigour 2 Bud-break earliness 3

Scion:rootstock diameter 4

Harmony

Medium to low overall. Performed better at Vorentoe than other sites. High to medium overall. Similar to Ramsey except for low yields at Vorentoe.

Similar to Ramsey at all sites except Begin where it was less vigorous. Variable. Similar to Ramsey at Yarona. Lower at Begin and Buffelskraal. Low at Vorentoe.

Medium to late overall and at all sites

Optimal: Vorentoe. Yarona. Not optimal: Begin. Buffelskraal. Denau. Optimal: Begin. Buffelskraal. Yarona. Not optimal: Denau. Vorentoe. Optimal: Buffelskraal. Denau. Yarona. Not optimal: Begin. Vorentoe. Optimal: Begin. Buffelskraal. Denau. Vorentoe. Not optimal: Yarona. Optimal: Buffelskraal. Vorentoe. Yarona. Not optimal: Begin. Denau.

Paulsen 1103

Late overall. Medium to late at individual sites.

Ramsey

High overall and at all sites.

High at all sites.

Early to medium overall and at all sites.

Richter 110

High to medium overall. Variable performance at individual sites.

Low at all sites except Yarona where it was similar to Ramsey.

Late overall. Medium to late at individual sites.

RS-3

Similar to Ramsey overall and at all sites.

Medium to low at all sites except Buffelskraal where it was similar to Ramsey. Medium to low at all sites except Buffelskraal where it was similar to Ramsey.

Early overall. Early to medium at individual sites.

RS-9

Low overall and at individual sites.

Early to medium overall. Early at Begin and Denau and medium at Yarona. Medium to late overall but variable at individual sites. Early at Yarona but late at Begin and Denau.

Optimal: Begin. Buffelskraal. Vorentoe. Yarona. Not optimal: Denau.

Ruggeri 140

Low overall and at individual sites.

Similar to Ramsey at all sites.

Optimal: all sites.

SO 4

High overall and at all sites.

Variable. Similar to Ramsey at Vorentoe. Lower at Begin and Buffelskraal. Low at Yarona.

Medium overall. Medium to late at Denau and late at Begin and Yarona.

Optimal: Buffelskraal. Denau. Not optimal: Begin. Vorentoe. Yarona.

1 Yields differed between rootstocks for all sites combined as well as at Begin, Vorentoe, and Yarona individually. 2 Vigour is based on cane mass. Vigour differed between rootstocks at Begin, Denau, Vorentoe, and Yarona individually. 3 Earliness differed between rootstocks for all sites combined as well as at Begin, Denau, and Yarona individually. 4 Ideal scion:rootstock diameter is 0.9–1.1. Ratios outside this range indicate less optimal scion:rootstock compatibility. It differed between rootstocks at all sites individually.

BEYOND THE BUNCH • 9 • QUARTER 2 • 2026

Table 2. Fertility and productivity traits of rootstocks in Phase 1. Ramsey is the control.

Rootstock

Bunch:shoot 1

Bunches per vine 2

Bunch mass 3

Berry mass 4

Harmon y

Medium to low.

Moderate.

Similar to Ramsey overall and at Begin. Medium to low at Yarona.

Low overall. Variable. Similar to Ramsey at Yarona. Higher at Denau and lower at Begin. Similar to Ramsey overall and at all sites except Denau where it was higher. High overall and at individual sites except Denau where it was moderate to low. Similar to Ramsey overall and at Begin and Denau. Lower at Yarona. Similar to Ramsey overall and at Denau and Yarona. Lower at Begin. Low overall. Lower than Ramsey at Begin and Yarona. Similar at Denau. Similar to Ramsey overall and at individual sites.

Paulsen 1103

High to medium.

High.

Similar to Ramsey overall and at Begin. Medium at Yarona. High overall. Not significantly different to other rootstocks at Begin. Low overall and at individual sites. Similar to Ramsey overall and at Begin. Medium to low at Yarona. Low overall and at individual sites. Similar to Ramsey overall and at individual sites. High overall. Similar to Ramsey at Begin and medium at Yarona.

Ramsey

Higher at Yarona relative to Buffelskraal.

High.

Richter 110

High.

Low.

RS-3

High to medium.

High.

RS-9

Low.

High.

Ruggeri 140

Higher at Yarona relative to Buffelskraal.

Moderate.

SO 4

High to medium.

High.

High overall. Similar to Ramsay at individual sites.

1 The ratio of bunches to shoots differed between rootstocks at Buffelskraal and Yarona. This ratio is a measure of fertility. 2 Bunches per vine differed between rootstocks at Yarona. 3 Bunch mass differed between rootstocks for all sites combined as well as at Begin and Yarona individually. 4 Berry mass differed between rootstocks for all sites combined as well as at Begin, Denau, and Yarona individually.

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KEBO TOOLO

The first steps of a six-year-long journey of rootstock evaluation.

BEYOND THE BUNCH • 10 • QUARTER 2 • 2026

Table 3. Bunch and berry quality traits of rootstocks in Phase 1. Ramsey is the control.

Acids and sugars

Rootstock

Bunch density 1

Shatter 2

TSS 4

TTA 5

TSS:TTA 3

Harmony

Begin: less ideal. Denau: ideal. Begin: less ideal. Denau: ideal.

Ideal.

Similar to Ramsey. High.

High to medium.

Paulsen 1103

Ideal.

Similar to Ramsey overall but lower at Begin. Moderate. Not significantly different to other rootstocks at Begin. High overall and at Begin. Similar to Ramsey overall but higher at Begin. Similar to Ramsey overall but lower at Begin. Similar to Ramsey overall but lower at Begin.

Similar to Ramsey. High.

Ramsey

Ideal.

Moderate to low.

Not significantly different to other rootstocks.

Richter 110

Begin: less ideal. Denau: ideal.

Less ideal.

Similar to Ramsey. High.

Medium to low.

RS-3

Ideal.

Similar to Ramsey. Low.

RS-9

Less ideal.

Similar to Ramsey. Low.

Ruggeri 140

Begin: less ideal. Denau: ideal.

Ideal.

Similar to Ramsey High.

SO 4

Begin: less ideal. Denau: ideal.

Ideal.

Similar to Ramsey. High.

1 Bunch density differed between rootstocks at Begin and Denau. 2 Shatter only differed significantly between rootstocks at Yarona. 3 TSS:TTA differed between rootstocks for all sites combined as well as at Begin individually.

4 TSS only differed significantly between rootstocks at Yarona. 5 TTA only differed significantly between rootstocks at Begin.

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The rootstock trials underway at Vorentoe in the Olifantsriver region.

BEYOND THE BUNCH • 11 • QUARTER 2 • 2026

Phase 2

had among the highest values for bunches per vine and bunch and berry mass. No other rootstock had among the highest values for all three of these traits. Yarona The rootstocks had similar yields at Yarona, again with the exception of the lower-yielding GRN-2 and GRN-4 (compared to the top-performing Ramsey and Kingfisher). Ramsey and Minotaur had among the highest values for bunches per vine and berry mass. First impressions When considering performance across all sites, the top yielding rootstocks were Kingfisher, Minotaur, and Ramsey. Of these, Minotaur was significantly more vigorous and had a higher scion:rootstock diameter than Ramsey, but not than Kingfisher. At both JDK and Yarona, Freedom had high TSS, high titratable acidity (TTA), and low TSS:TTA. During ripening, it appears that its acids decline slowly relative to its sugars. So far, Ramsey, Kingfisher, and Minotaur show the most promise in phase 2, but keep in mind that several years of data still need to be collected and analysed.

As already mentioned, phase 2 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. Since this phase was only established in 2022, the first harvest at JDK and Yarona was in 2024, and at Excelsior in 2025. The summary that follows is based on the 2025–2026 season. Note that trials will continue At Excelsior, the only traits that differed significantly between rootstocks were scion:rootstock diameter, earliness of bud break, and total soluble solids (TSS). No rootstock had among the top values for all three traits. Minotaur showed potential compatibility and vigour problems at this site. JDK All the rootstocks had similar yields at JDK, except for GRN-2 and GRN-4, which had lower yields than the top performers (Ramsey and Minotaur). Ramsey also until 2028. Excelsior

Table 2. Site and trial characteristics for phase 2 (2022–2028). Excelsior

JDK

Yarona

De Doorns Hex River

Paarl Berg River

Kanoneiland Orange River

Location

Scion cultivar Vine spacing

Crimson Seedless

Sugrathirtyfive

IFG Ten

3.0 x 1.8 m

3.3 x 1.6 m

0–30 cm 30–60 cm General

Sand Sand

Loam Loam pH 5.9

Loam Loam pH 6.8

Soil

pH 6.1

Irrigation system

Micro-sprinklers

Drip

Micro-sprinklers

Trellis system

Gable

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BEYOND THE BUNCH • 12 • QUARTER 2 • 2026