Rootstocks: choose what is best for your crop

Researcher and rootstock specialist, Dr Piet Stassen, discusses the characteristics of high-potential stone-fruit rootstocks for South African conditions. This guide will help you to confidently choose a rootstock suiting your crop’s needs.

Not all soil problems can be rectified with rootstocks. The necessary soil preparation, effective drainage, initial nematode treatments, effective irrigation, well-rooted, hardened-off and healthy nursery material are part and parcel of a successful rootstock.

Timeous planning will ensure quality nursery trees with adequate feeder roots. Propagation techniques must be upgraded and adapted as necessary to deliver such quality plant material. When planted, these trees must grow and perform optimally with zero die-back.

We are fortunate to have rootstocks complementing our scion cultivars, which provide the grower with opportunities to positively increase yield and fruit quality in their orchard. However, this is only possible if one begins with well-prepared soil medium, quality plant material and optimally managed orchard practises.

Dip all trees in Agrobacterium strain 84, both in the nursery and before planted in the orchard, to avoid serious crown-gall development. Paint the trunk with a white paint or copper solution — especially in sandy soils. The first year in the orchard is crucial to promote feeder-root development and vegetative growth.

Flordaguard

Peach x Prunus davidiana hybrid. P. davidiana is a wild peach species.

Excellent for sandy (and or stony) soil. For very low-chilling regions (even less than 200 Infruitec cold units, but also for higher chilling regions). Well-synchronised with early cultivars. Immune towards root-knot nematodes. Not for soils that can be wet or calcareous/high pH/carbonate or bi-carbonate soils. When ring-nematode numbers higher than 500/ 300 cm³ soil fruit weight negatively affected. Sensitive to bacterial and fungal infections. Short dormancy period and hardening off in the nursery may be a problem. Nursery trees may have inadequate reserves and then trees must be headed back after planting in the orchard. Red-coloured leaves.

Atlas

Multispecies, complex hybrid.

A consistently good performer over a wide range of soil types. Very good fruit size. Stronger root system compared to Viking. Grow and performs well in sandy soil, also in sandy, calcareous soil. Show some lime-induced iron chlorosis in free lime conditions, but influence on performance not significant. Needs about 300 and more Infruitec cold units. Fruit a few days later compared to trees on Flordaguard. Tolerant to bacterial and fungal infections. Host to ring nematodes but that does not affect yield and fruit size. Resistant to root-knot and moderate tolerant to root-lesion nematodes.

Cadaman

Peach x P. davidiana. Also known as Avimag.

A strong grower and good for sandy soils (it is 12% stronger compared to GF 677). Good yield and fruit size. Sensitive to bacterial and fungal infections. Only minor yellowing in calcareous soil. Resistant to some root-knot, moderate tolerant to ring and sensitive to root-lesion nematodes. Good host to ring nematodes but can still have good yield and fruit size.

Viking

Multispecies, complex hybrid.

Good overall rootstock for many soils but not recommended for sandy (stony) soil. Can easily dehydrate in sandy soils during warm summer months and then become more sensitive to ring-nematode infestation. Fruit later compared to Flordaguard and Kakamas seedling, same as Atlas. Take caution not to let roots dry out before planting. More tolerant to bacterial and fungal infections compared to peach x almond hybrids. Resistant to root-knot nematodes. More sensitive to root-lesion nematodes than Atlas.

GF 677

Peach x almond hybrid.

Take and rooting % low from hardwood cuttings and many nursery trees have limited feeder roots. This can cause die-back of trees after planting in orchards, especially in stressful situations (sandy soil, ineffective irrigation, clay soils). External biotic and abiotic factors predispose trees to diseases. Very sensitive to wetness especially also when feeder roots are limited—this can cause fungal infections (Phytophthora cactorum and others). Very sensitive to root-knot and root-lesion nematodes and crown gall. GF 677 is the standard for calcareous soils and performs well in the Robertson/Bonnievale region and also in moderately saline conditions. Other propagation methods should be used to ensure successful nursery trees. Smaller fruit with nectarines compared to Atlas and Cadaman.

SAPO 778

Complex hybrid.

Not recommended for low-chill regions (˃100 to 350 Infruitec cold units), or early cultivars. Synchronisation between early cultivars and this rootstock in stress situations (sandy soil/ fluctuating water tables) can cause fungal infections (Leucostoma). Ripening is delayed. Sensitive to calcareous or saline soil. Tolerant against ring nematodes. Very good fruit size.

Garnem

Nemared peach x almond hybrid.

Red-coloured leaves and strong grower. Good host for ring nematodes but performs well in terms of yield and fruit size even when high numbers occur. Resistant to root-knot nematodes but has increased susceptibility to bacterial canker. Peach x almond hybrids are sensitive to bacterial and fungal infections when external biotic and abiotic factors predispose trees to diseases. A 20% stronger grower than GF 677. Not enough information regarding sandy soils. Included in new evaluation trials.

Guardian

Nemaguard peach cross.

Not enough local information. Included in new evaluation sites especially in sandy soils. Fruit weight suspicious—poor fruit weight, the same as a Kakamas seedling under stress conditions, but yield is better than Kakamas seedling. Not for calcareous soil. Vigour more like Atlas but less than Garnem. Resistant to root-knot nematodes. Host to ring nematodes but less so than Marianna. According to overseas information this rootstock is resistant to bacterial diseases.

Marianna

P. cerasifera x P. munsoniana.

Very sensitive to ring nematodes, bacterial canker, and fungal infections especially so in sandy soil (external biotic and abiotic factors predispose trees to diseases). Small fruit when stressed and high numbers of ring nematodes occur. Shallow horizontal growing rootstock (need about 40mm good soil) therefore ideal for soil with clay layers in underground. Good rootstock for medium to high-potential soil.

Maridon

Tetraploid of Marianna.

Shallow horizontal growing rootstock (need about 40 mm good soil) — ideal for soil with clay layers in underground. Relatively less sensitive to bacterial canker than Marianna. Flowers abundantly in Little Karoo region putting fruit size under pressure. High numbers of ring nematodes probable and moderately sensitive for calcareous soil (less than Flordaguard, SAPO 778 and Kakamas seedling). Small fruit when stressed and when high numbers of ring nematodes occur.

Kakamas seedling

Peach seedling selection.

A semi-dwarfing rootstock. Easily stressed on sandy soils and during warm autumns bud drop occurs. Fruit size negatively influenced by stress conditions (sandy soil, root-knot nematodes, high pH, saline, and wetness). Good rootstock for medium to high-potential soil, free from any stress factors or limitations. Sensitive to crown gall — must be treated with Agrobacterium strain 84. Not recommended for sandy soils where yield and fruit weight are negatively affected. Rather use Flordaguard or Atlas, depending on the site conditions.

Royal seedling

Apricot seedling.

Compatible with all South African apricot scion cultivars. Excellent for well-drained shale soils, sensitive to wet soils. To use any of the other rootstocks available to the peach and plum growers, Royal interstem is a prerequisite to avoid breakage at the bud union. Very sensitive to bacterial and fungal diseases.

NOTE: Please refer to Fresh Quarterly issue 6 for an updated version of this article.