Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
University of California
Walnut Scion & Rootstock Improvement

Air Layering

 

Plants recently rooted by air-layering now potted and temporarily placed under a shade cloth.
Plants recently rooted by air-layering now potted and temporarily placed under a shade cloth.
We have achieved considerable progress in developing air layering as a method for clonal propagation of Juglans species. Variations in air layering were tested successfully to root actively growing shoots of containerized seedlings, clonal material grafted onto containerized rootstock, and most importantly basal sprouts of mature trees growing in the field (the Mother Trees used to generate seedling test material and mapping populations). 

Air layering has been most successful when we have utilized plasticized peat plugs (Q-Plugs®) ~ 5 cm long x 3 cm diameter as the layering material. The layering process involves making three 4 cm long longitudinal cuts in the bark near the base of shoots, girdling below the wound site, wrapping the wounded site with paper towel material wet with 8000 mg/l K-IBA, and covering the paper towel material with a longitudinally split water soaked plasticized peat plug. The plasticized peat plug needs to kept wet by: 1) daily watering by hand (labor intensive) or; 2)using a drip irrigation system or; 3) wrapping in aluminum foil with weekly watering or; 4) in the case of basal sprouts on mature Mother Trees growing in the field, covering the plugs with wet pine shavings and watering weekly.

Containerized plants of J. microcarpa, J. major, J. nigra and J. cathayensis ‘#21’ have all been  rooted successfully (50- 100%) in three to eight weeks using these methods. Rooted shoots were severed below the rooted area and planted into one liter containers. Survival of these rooted plants has been 75- 100%. Rooting and survival have both varied depending on species, with J. microcarpa being the most successful.
Basal sprouts from the two J. microcarpa Mother Trees that were attempted were successfully rooted and propagated using this air layering process. However, when air layering was attempted on canopy shoots of a wide variety of other Juglans species in the field, only a single shoot on one J. ailantifolia Mother Tree rooted, and it rooted only sparsely. This suggests that inducing basal sprouts on mature trees of interest may be necessary in order to obtain successful air layering production of clonal replicates disease resistance testing.

Fig. 16. Early root emergence from a hand-watered air-layer
Fig. 16. Early root emergence from a hand-watered air-layer
Fig. 17. Air-layering using drip emitter system to maintain uniform moisture.
Fig. 17. Air-layering using drip emitter system to maintain uniform moisture.
Fig.18. Air-layering - roots emerging from an irrigated stabilized peat plug.
Fig.18. Air-layering - roots emerging from an irrigated stabilized peat plug.

Fig. 19. Abundant roots emerging from drip-irrigated stabilized peat plug.
Fig. 19. Abundant roots emerging from drip-irrigated stabilized peat plug.
Fig. 20. Multiple air-layers on a single seedling of interest.
Fig. 20. Multiple air-layers on a single seedling of interest.
Fig. 21. Rooted air-layered seedling ready for planting.
Fig. 21. Rooted air-layered seedling ready for planting.

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