Choosing table-grape rootstocks

In table-grape production, rootstock choice plays a crucial role in helping vines thrive. By Kebo Toolo (Provar)

Rootstocks function as "bodyguards", shielding scion cultivars from the harsh effects of challenging climates and unfriendly soils and can boost the quantity and quality of the crop. Like picking the right tools for a job, producers choose rootstock varieties based on their unique traits. But here is the twist: SA has such a diverse range of climates and soils that it practically demands the use of special rootstocks for each environment.

SATI is funding two phases of rootstock evaluations which are being managed by Provar, an independent evaluation company. Phase I was planted in 2019, and Phase II in 2022. In the Phase I rootstock plantings, five scion varieties are being evaluated in five different growing environments on eight different rootstocks (Harmony, RS-3, RS-9, Ruggeri 140, SO4, 1103 Paulsen, Richter 110 and Ramsey).

The Phase I evaluations mainly include older rootstocks that are being evaluated on newer, more relevant scion varieties. In the Phase II rootstock plantings, three scion varieties are being evaluated on seven rootstocks in three different growing environments. Several new rootstock varieties are being evaluated in these trials, namely GRN-2, GRN-4, Minotaur, Kingfisher, Freedom, 1103 Paulsen and Ramsey.

While data capture on Phase II has already commenced, it is too early to provide results. This article presents results from Phase I evaluation trials, focusing on four key traits (shoot weight, yield, bunch weight and berry weight).

When data analysis is performed across different environments, things can get a bit tricky. The way rootstocks and scion combinations behave is much like assembling a puzzle. To simplify the results, they will be broken down, one environment at a time, to indicate different responses of rootstock and scion combinations.

A "bubble graph" is used to show how the rootstocks differ from one another per environment. Average yield per vine and pruned shoot weight (representing vigour) are presented on the axes, and the size of each circle represents average bunch weight per rootstock.

Olifants River region – IFG 68-175 ('Sweet Celebration'™)

1103 Paulsen and SO4 were the best performers when it came to shoot weight and produced heavy bunches, but this didn't translate into high yields (Figure 1). Ramsey was highest with regard to yield. Ruggeri 140 also performed well and both stood out from the rest, even though they did not produce the heaviest bunches and did not induce vigorous growth. In terms of berry weight, Ruggeri 140 and SO4 were the best achievers. SO4 produced the heaviest bunch weight but was not significantly different from 1103 Paulsen and Ramsey.