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

Stool Layering

One method of stool bedding involves grafting scions from the selected Mother Trees onto seedling Paradox rootstocks (easy to distinguish from mother tree scions) in the spring. The grafted trees are planted in a 30 cm deep wood shavings bin (stool bed) in a greenhouse so that the shoots developing from the Mother Tree scions can grow in the dark and as a result become etiolated.

Five to ten shoots new shoots can develop from each scion, depending on the species of the Mother Tree. Such shoots have much greater potential for adventitious root initiation than green shoots in Juglans and many other species (Hartmann et al., 2010). To induce the initiation of adventitious roots on the etiolated mother tree scion shoots, the base of the shoots are treated with equal concentrations of K-IBA and NAA at 5000 mg/L in lanolin paste. Longitudinal incisions are made in the treated areas to facilitate uptake of the root inducing compounds and the stem below the treated areas is girdled with a wire tightened around the stem. After treatment, a 30 cm depth of wet wood shavings is placed around the plants to cover the treated area. The shavings later removed and the rooted shoots are severed and planted in containers for further development and assessment of disease resistance.

Fig. 1. Greenhouse stooling bed.
Fig. 1. Greenhouse stooling bed.
Fig. 2. Stooling process using individual pots.
Fig. 2. Stooling process using individual pots.
Fig. 3. Roots developing in greenhouse stooling bed.
Fig. 3. Roots developing in greenhouse stooling bed.
 

 

Fig. 4. Roots developing in greenhouse stooling bed.
Fig. 4. Roots developing in greenhouse stooling bed.
Fig. 5. Plants removed from greenhouse stooling bed.
Fig. 5. Plants removed from greenhouse stooling bed.
Fig. 6. Roots developed on etiolated stems of plants in stooling bed.
Fig. 6. Roots developed on etiolated stems of plants in stooling bed.
 

Fig. 7. Roots developed in stooling bed on new etiolated shoot.
Fig. 7. Roots developed in stooling bed on new etiolated shoot.
Fig. 8. Roots developed from etiolated scions using individual pot method.
Fig. 8. Roots developed from etiolated scions using individual pot method.

 

A second stool bedding approach involves in situ rooting of sprouts at the base of Mother Trees. This method enhances the likelihood of successfully rooting shoots from reproductively mature Mother Trees (Hartmann et al., 2010). If mother trees do not naturally have basal sprouts, suckers can be induced by girdling (removal of about a one inch strip of bark down to the cambium) half the circumference of the trunk in early spring, about one foot above ground level where latent shoot buds are most likely to be located.

To induce rooting in the late spring and early summer, basal spouts about 2-3 feet tall are girdled near the base by removing a five mm wide piece of bark from their circumference, making three one inch long longitudinal wounds through the bark above the girdle, applying a piece of 8000PPM K-IBA soaked paper toweling over the wounds, and then finally, covering the girdled and wounded area with a stabilized peat plug (Q-Plug®). The treated shoots are then covered with moist pine shavings enclosed in hardware cloth. After six to eight weeks incubation in this moist environment, rooted shoots are detached below the peat plug and containerized in a greenhouse for subsequent growth and assessment for disease resistance.

Fig. 9. Stooling bed  propagation of Mother Tree suckers (2).
Fig. 9. Stooling bed propagation of Mother Tree suckers (2).
Fig. 10. Stooling bed  propagation of Mother Tree suckers (1).
Fig. 10. Stooling bed propagation of Mother Tree suckers (1).
Fig. 11. Girdling shoot below K-IBA application.
Fig. 11. Girdling shoot below K-IBA application.

Fig. 12. K-IBA application in stooling bed
Fig. 12. K-IBA application in stooling bed
Fig. 13. Removal of sawdust to expose shoots.
Fig. 13. Removal of sawdust to expose shoots.
Fig. 14. Roots developed on Mother Tree suckers.
Fig. 14. Roots developed on Mother Tree suckers.
Fig. 15. Planted clonal copies of rooted shoots.
Fig. 15. Planted clonal copies of rooted shoots.
 

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