Rootstocks for stone fruit

The information is summarised in four tables, with additional notes on each rootstock given separately.
Table 1 contains information on plant attributes. A rootstock’s parentage determines characteristics such as tolerance to calcareous soils and salinity and susceptibility to fungal infections and nematodes.
Table 2 shows the soil texture preferences of stone-fruit rootstocks. Soil texture plays an important role in rootstock performance.
Table 3 provides soil and climatic preferences. Most stone fruits are sensitive to salinity. Electrical conductivity of more than 300 mS/m and sodium levels of more than 9 mg/ℓ in irrigation water constitute very high salinity for stone fruit. Refer to the table footnotes for levels that will impact production.
Rootstocks with plum parentage can tolerate higher salinity than those with peach parentage. Peach-almond hybrids have intermediate tolerance.
All available stone-fruit rootstocks are sensitive to wet conditions. Bacterial and fungal infections are more common in wet and low-lying areas where fluctuating water tables may occur during heavy rains.
Table 4 summarises the resistance of the different rootstocks to nematodes and diseases. Nematode damage is often under-estimated because the culprits are in the soil, and aboveground symptoms are non-specific. Young root systems are more sensitive to high nematode numbers than established ones.
Factors such as nematode resistance, drought tolerance, and chill requirement shouldn’t be considered in isolation. Healthy, vigorous orchards result from the sum of all these characteristics. A holistic approach is the only way to achieve maximum production per hectare.
Rootstock choice impacts an orchard’s lifetime performance. Growers should consult a specialist technical adviser when making their selection.

Notes on individual rootstocks
Atlas is not recommended for early flowering cultivars because bud break occurs nearly a month later on this than on other rootstocks, resulting in delayed harvest maturity.
Based on the recently completed trials, Atlas seems a good choice for very sandy soils next to the Berg River in Simondium, where a combination of bacterial canker, fungal disease, and high nematode numbers may cause dieback.
It’s also a good choice for well-drained soils on mountain slopes.
Plums on Atlas are less vigorous and require less summer pruning than on GF 677 but are not stunted.
On Barrier (new in table), excessive vigour of peaches and nectarines can lead to heavy shading within the canopy, resulting in uneven ripening and a higher percentage of uncoloured fruit. The vigour may thus be better suited to multileader trees.
According to international data, Barrier has some tolerance to free lime-induced chlorosis and ring nematodes. It is highly susceptible to root-lesion nematodes.
Barrier was among the best-performing rootstocks in a high-potential soil in Limpopo, so may not have a very high chilling requirement. It also performed well in sandy soil in Slanghoek and does very well in the Klein Karoo.
Cadaman (also known as Avimag) trees are 12% larger than those on GF 677. They have good yields, fruit size, and high total soluble solids, making Cadaman a potential alternative to GF 677, albeit less tolerant of free lime.
Flordaguard is generally excellent for sandy or stony soil but did not perform as well as Guardian and Barrier in Slanghoek, or Atlas next to the Berg River in Simondium.
Flordaguard did perform well on clay soil in Limpopo.
It’s well-synchronised with early cultivars, but its short dormancy may lead to problems with hardening off in the nursery. Nursery trees may have inadequate reserves, so they must be headed back after planting in the orchard.
Trees on Flordaguard can bear fruit with
a tip in some low-chill regions.
Garnem grows 20% more strongly
than GF 677.
Garnem did not perform well in sandy soil in Slanghoek and showed high tree mortality next to the Berg River in Simondium. Although it produced good plum size and yield in Robertson, yields were higher with GF 677.
GF 677 is the best rootstock for calcareous soils and is good for stony soils and moderately saline conditions. It performed well in the Robertson and Bonnievale areas. According to the literature, GF 677 is a good choice in replant situations on high-pH soils.
Nectarines on GF 677 produce smaller fruit compared to trees on Atlas and Cadaman. However, plums set better on GF 677 than on most other rootstocks. Note that colour development is poor for some cultivars on GF 677.
The take and rooting percentage from hardwood cuttings of GF 677 is low, and many nursery trees have insufficient feeder roots. This can cause tree dieback after planting in orchards, especially in stressful situations such as inefficient irrigation or sandy or clay soils. Therefore, other propagation methods are recommended.
The trees on Guardian are less vigorous than those on Flordaguard, Garnem, and Mariana but slightly larger than those on Atlas and GF 677.
Guardian is very precocious, so timely thinning is important to ensure good fruit size. It produced good fruit size on the sandy soil in Slanghoek, where it was the highest-yielding rootstock. Like Kakamas seedling, Guardian can bear small fruit when stressed.
Its production performance in very sandy soil next to the Berg River in Simondium was average, but production away from the river in Simondium and Franschhoek is excellent. Commercial plantings in Robertson are very productive.
According to overseas information, Guardian is resistant to bacterial diseases.
Marianna is compatible with plums and non-Bulida-related apricots. It remains a good choice for medium to high-potential soils, but its performance in Robertson was not as good as Atlas, Garnem, and GF 677.
Marianna needs about 40 cm of good soil. Its shallow horizontal growth makes it ideal for soil with subsurface clay layers. Of the plum rootstocks, Marianna has the highest tolerance to wet conditions.
High tree mortalities in Simondium were consistent with Marianna’s sensitivity to stress-related infections.
Maridon is a less-vigorous plum-specific rootstock. It’s a good choice for netted orchards, excessively vigorous cultivars, or high-potential soils.
Like Marianna, Maridon has shallow, horizontally growing roots and needs about 40 cm of good soil. It’s ideal for soil with subsurface clay layers.
Maridon flowers prolifically in the Little Karoo, putting fruit size under pressure. Stress due to poor soils and high numbers of ring nematodes can also lead to small fruit.
Kakamas is a good rootstock for medium to high-potential soils and stress-free conditions, but it’s easily stressed on sandy soils. Stress from sandy soils, high pH, salinity, wetness, or root-knot nematodes will reduce fruit size and yields.
Atlas, Flordaguard, and Guardian are better options for sandy soils.
Warm autumns lead Kakamas to drop its buds in the subsequent spring.
Kakamas is sensitive to crown gall
and must be treated with Agrobacterium strain 84.
OSM 99-3 (new in table) and Flordaguard showed similar size and performance in Limpopo. In Slanghoek, OSM 99-3 produced a smaller tree with better than average yield but smaller fruit size than Guardian.
OSM 99-3 was bred for tolerance to root-knot nematodes, but its susceptibility to nematodes is unclear.
Rootpac-70 (new in table) was bred for adapta-bility to Mediterranean conditions. It’s compatible with peaches, nectarines, and plums and has a higher yield efficiency than most rootstocks. Rootpac-70 may be suitable for higher-density plantings.
According to international data, Rootpac-70 is resistant to root-knot nematodes, tolerates free lime, and has improved tolerance of wetness and soil fungi. In local trials, it maintained good fruit size in sandy soil despite high ring-nematode numbers. Rootpac-70 performed acceptably in Limpopo but not better than Flordaguard.
Royal seedling is an apricot-specific rootstock compatible with all South African apricot scion cultivars. A Royal interstem is necessary to avoid graft failure when using other rootstocks.
Royal seedling is excellent for well-drained shale soils.
As this is a high-chill rootstock, SAPO 778 is not recommended for low-chill regions or early cultivars – climate change may further reduce its suitability in some areas. It can have synchronisation problems with early cultivars.
When stressed by sandy soils or fluctuating water tables, SAPO 778 can synchronise poorly with early cultivars, predisposing it to fungal infections.
SAPO 778 performed very poorly in
the sandy soil and stressful conditions next to the Berg River in Simondium. It generally performs poorly after warm winters in
this region.
Viking had better production performance than Cadaman in calcareous clay soils with pH >7. Fruit maturity in Viking is similar to Atlas, but later than Flordaguard and Kakamas seedling.
Viking dehydrates easily in sandy soils during warm summer months, becoming more sensitive to ring-nematode infestations. Take care not to let roots dry out before planting.
It’s not recommended for very late cultivars, as it’s one of the earliest rootstocks to enter dormancy.

Contributors

• Dr Piet Stassen supplied the
  information for the original 2018 and 2019 articles. Petru du Plessis and other technical advisers
  contributed inputs.
• Chad van Wyk of Provar provided the updated information, with inputs from rootstock committees and the following technical advisers:
  • Nigel Cook
  • Rudolph Cronjé
  • Petru du Plessis
  • Andrew Hacking
  • Charl Stander.

BOX
Consideration when choosing rootstocks for stone fruit
The following are some of the factors determining rootstock suitability.
Although the information for the various rootstocks is summarised in the tables and notes, growers must always consult their technical adviser when
selecting rootstocks.

• Fruit type and scion-rootstock compatibility.
• Soil texture, depth, and limiting factors like free lime.
• Chilling requirement of both the rootstock and scion. The rootstock must not have a higher requirement than the scion. Both must be suited to the region.
• Susceptibility to bacteria, fungi, and nematodes.
• Effect on fruit quality (size, shape, sugars, and defects).
• Vigour, especially when planting under nets.
• Entrance into dormancy.
• Earliness – very closely linked to chilling requirement.
• Plant material. The propagation method (cuttings, seeds, or tissue culture), and whether trees are open-rooted or containerised, have far-reaching implications.

INTRO BOX

Updated guide to stone-fruit rootstocks

With the recent completion of four trials, it was time to update the Hortgro summary of stone-fruit rootstocks. Also read about an innovative stone-fruit orchard at Roodezand near Tulbagh, as well as another of the Hortgro demonstration orchards at Lindeshof in the Koue Bokkeveld.
For similar content, visit www.freshquarterly.co.za to download your free copy of Fresh Quarterly, the Hortgro Science technical magazine.

Opgedateerde gids vir steenvrugonderstamme

Met vier onderstamproewe onlangs voltooi was dit tyd om die Hortgro-opsomming van steenvrugonderstamme op te dateer. Lees ook omtrent ’n innoverende steenvrugboord by Roo-dezand naby Tulbagh, sowel as nog een van die Hortgro-demonstrasieboorde by Lindeshof in die Koue Bokkeveld.
Vir soortgelyke artikels, besoek www.freshquarterly.co.za om ’n gratis digitale eksemplaar van Fresh Quarterly, Hortgro Science se tegniese tydskrif, te bekom.