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202309 Fresh Quarterly Issue 22 02 South African Rootstock Trends Web
Issue 22September 2023

South African apple-rootstock trends

The industry has come a long way since M.793 ruled the roots. Three technical advisers discuss the journey and where we might go next. By Anna Mouton.

The story of M.793 begins in 1920 when selective breeding for woolly apple aphid resistance started at the John Innes Horticultural Institute at Merton in England. It was sent to South Africa for trials in 1935 and introduced to the industry in 1953. Nearly 40% of apple trees sold in the Western Cape were budded on M.793 by 1970.

Nursery production of M.793 peaked at roughly 50% — about 800 000 — of all rootstocks in 2010 but has been declining ever since. Only 53 000 M.793 rootstocks — about 1.5% of all rootstocks — were planted for budding in 2023.

“M.793 was the industry standard when I started my career,” relates Angelique Pretorius, technical manager at Kromco. Trees were usually planted at 4.0 x 1.5 m. She notes that there were also older orchards of 4.5 x 1.5–1.75, and even some unsuccessful attempts at higher density orchards with trees on M.793 spaced at 1 m.

Graeme Krige, technical adviser and general manager of Fruitmax Agri, saw MM.109 replacing M.793 in the early years of his career. “There wasn’t much difference between them, but there was a belief that the step-ups in production were faster with MM.109 than M.793. This was probably because replanting increased and MM.109 was slightly more vigorous.”

Both M.793 and MM.109 were selected for woolly apple aphid resistance, but mutated strains of woolly apple aphid that could overcome the resistance had already emerged in Elgin by 1964.

In 2015, the nursery production of MM.109 overtook M.793 for the first time. Although the popularity of MM.109 is also waning, it nonetheless accounts for 12% of rootstocks planted for budding in 2023. But in recent years, both M.793 and MM.109 have been overshadowed by their older relative: M.7.

Older rootstocks prove their worth

Plantings of M.7 increased for the first nearly two decades of the 2000s but dropped from a high of 46% in 2019 to a mere 32% in 2022. However, it remains the most sought-after rootstock in South Africa, comprising about 35% of those planted for budding in 2023.

“M.7 was originally planted on better soils, at higher densities of 3.75 x 1.25–1.5 m,” recalls Pretorius. Whereas MM.109 can be 80%–90% and M.793 70%–80% of seedling vigour, M.7 is closer to 55%–65%, placing it in the semi-vigorous category.

The extraordinary thing about M.7 is that it is one of the original Paradise rootstocks collected by East Malling in 1912 and 1913. It is believed to trace its ancestry to France in the 1600s. The dwarfing M.9 — also known as Jaune de Metz — likewise comes from France and dates from 1879.

Although M.9 has been a favoured rootstock in Europe and the United States for decades, it has been slow to catch on in South Africa. Three clones are available locally: EMLA, Nic29, and T337. Until 2019, they collectively comprised less than 5% of rootstocks planted annually. In 2021, this number shot to nearly 10%, and M.9 seemed to be on an upward trajectory.

“At this stage, we want to plant as much M.9 as possible,” says Willie Kotze, technical adviser with Dutoit Agri. “Where we have poorer soils or more challenging scion cultivars, we plant M.7.”

Kotze partly credits his enthusiasm for M.9 to the Orchard of the Future project. Dutoit Agri had a participating block of Rosy Glow on MM.109 with an M.9 EMLA interstem. “It was a stepping stone for us. Even before the project ended, we could see from the yields and the pack-outs that we needed to make a drastic change.”

He adds that Johan Kotze, head of Dutoit Agri: Eastern Cape, was an early advocate for M.9 within their company. “He planted the first commercial orchards. When those came into production, we all realised he was right.”

“We call M.9 dwarfing, but it’s actually just super efficient in fixing dry mass,” comments Krige. “If you manage it correctly, that dry mass goes into fruit. So M.9 brings great opportunities, which is why the rest of the world boarded the M.9 train long ago.”

The rise of Geneva rootstocks

Until 2020, more than 95% of South African nursery trees were grafted on Malling, Merton, and Malling-Merton rootstocks. But since then, the production of Geneva rootstocks has exploded, from an insignificant 6% in 2020 to nearly a quarter in 2022. Of the rootstocks planted for grafting in 2023, 44% are Genevas.

Among the Geneva rootstocks, G.778 is the undisputed leader, making up nearly a fifth of all nursery trees lifted in 2022 and about 27% of rootstocks planted for grafting in 2023. At approximately 85% of seedling, it is more vigorous than either MM.109 or M.793, which raises red flags among some technical advisers.

“G.778 is very popular right now because it fills its space quickly and gives amazing yields,” says Kotze. “But I think that, five years from now, keeping those trees in the same space will be challenging, and you might get the production, but you’ll struggle to get the quality and pack-outs because the canopies will be too shaded.”

Pretorius agrees. “I see too many vigorous Geneva selections planted at high densities. We don’t want to go back to root pruning, girdling, and trying to manage large canopies, and at the end of the day, we don’t get the colour development that drives profitability.”

“Remember that when you plant an orchard, the rootstock is just one part of the puzzle,” says Krige. “If you decide to plant 4 x 1.5 m, then you have the volume to fill and need something to do that for you. But growers should be wary of planting vigorous rootstocks too close together.”

Besides G.778, there are three other Geneva rootstocks — G.202, G.222, and G.228 — on the official varietal list and several others that are not on the list but are being propagated for evaluation purposes only.

“We are planting our first commercial blocks on G.222,” says Kotze. “We see G.222 as a replacement for M.7, but we plant it a little closer — 3.5 x 1.0–1.25 — than M.7.”

Kotze has observed that Geneva rootstocks seem to have greater tolerance to woolly apple aphids than M.7 or M.9. He acknowledges that this needs to be experimentally confirmed. Still, he hopes that new rootstocks may reduce woolly apple aphid pressures on growers trying to cope with the loss of crop-protection agents.

The rootstock road ahead

Looking to the future, Kotze would like to see precocious Geneva rootstocks that can replace M.9. “Dutoit Agri wants to plant dwarfing rootstocks. So far, there isn’t a Geneva in the M.9 vigour class that’s proved itself, but we have G.213 and G.757 on our short list.”

Kotze is impressed with the performance of G.757 in rootstock trials. Although it has similar vigour to M.9, it fills its space faster and is more productive.

Brazilian researchers have shown that certain Geneva rootstocks, notably G.213, have similar vigour to M.9 but better early cumulative yields and greater tolerance to replant disease. Trees grafted on G.213 had better branch angles and more branches in the upper canopy.

“I’m very excited about rootstocks that change the growth habit of the scion in especially warmer winter areas,” says Krige. “They are imparting low-chill behaviour — better breaks in better places. It would be fantastic if G.213 does this under our conditions.”

But he notes that growers already have access to efficient rootstocks across various vigour classes. “There are more options to match with cultivar, training system, soil, nets, etcetera — producers have more tools in their toolbox. And we now have rootstocks that bring disease tolerance to the party.”

When rummaging through the rootstock toolbox, the overarching goal remains to maximise Class 1 apples on the tree. “If you look at what we’re planting, the tendency is toward cultivars that must have red colour,” says Pretorius. “The advantage of high-density plantings is that the trees are simpler and less labour-intensive to manage.”

“With the right manipulations and management, I think you can get to the right fruit quality when using a more vigorous rootstock,” reflects Kotze. “But it requires a lot more inputs, and I don’t know if everyone always realises that.”

Notes on figures

Please note that the rootstock numbers differ from the number of trees established in orchards.

  • Data for 2012 and 2022 represent trees lifted in the nursery.
  • Data for 2023 represent rootstocks used for budding trees to be sold in winter 2023.
  • Data for 2024 represent rootstocks planted for budding in 2023.
  • Data include all rootstocks: certified, uncertified, and candidate.
  • Data was supplied by PlantSA.

 

202309 Fresh Quarterly Issue 22 02 South African Rootstock Trends Figure 1 Web

Figure 1: The most popular rootstocks as a percentage of all nursery trees produced for selected years.

202309 Fresh Quarterly Issue 22 02 South African Rootstock Trends Figure 2 Web

 

 

 

 

 

 

 

Figure 2: Dwarfing, semi-dwarfing to semi-vigorous, and vigorous rootstocks as a percentage of all rootstocks used for nursery-tree production.

Sources for numbers of rootstocks produced and planted

Kriel R. 2023. PlantSA figures for rootstock production from 2012–2024. (personal communication).

Strydom DK. 1970. Malling-Merton rootstocks. The Deciduous Fruit Grower 20(3).

Voigt F and Stassen PJC. 2014. The South African deciduous fruit industry’s apple rootstock scenario and future initiatives. Acta Hortic. 1058 pp465-470.

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