Propagation techniques for pome and small fruit crops by layering

Propagation by layering allows for obtaining high-quality nursery plants due to the stems' ability to form adventitious roots without prior detachment from the mother plant. In nursery production, this method is indispensable for obtaining own-rooted plants. Agronomists apply four main techniques, each having its own specific features depending on the crop being propagated.

• Depth of the trench for arching layering — 15–20 cm
• Height of pruning the mother plant for stool layering — 2–3 cm
• Depth of the furrow for trench layering — 5–8 cm
• Final hilling layer for stool layering — 25 cm
• Final height of the ridge for trench layering — 20 cm

Layering propagation technologies in the nursery

Arching layering allows for obtaining well-rooted plants within one growing season. In early spring, the upper part of a dormant one-year-old branch is placed into a trench 15–20 cm deep, and its end, at a distance of 20–25 cm from the tip, is directed vertically upward. The placed stem is covered with light composted soil. To stimulate root formation, the branch is bent sharply or the bark is girdled at the bend. This method is optimal for obtaining nursery plants ready for permanent planting of quince, peach, chokeberry, gooseberry, hazel, as well as clonal rootstocks.

Stool layering (vertical layering) serves as the main method for propagating clonal apple rootstocks and pear. Early in the spring, mother plants are cut to a height of 2–3 cm from the ground or slightly deeper to form stool beds, on which one-year-old shoots grow. As they develop, multiple hilling with moist soil is performed. At the end of the growing season, the ready layers are separated from the mother plants.

Rules for hilling vertical layers:

• The first hilling is performed to half the height of the grown shoots.
• Filling with moist soil is repeated 4–5 times during the growing season.
• The final thickness of the soil layer over the base of the shoots is brought to 25 cm.

Trench layering (horizontal layering) significantly increases nursery productivity. When using it, the yield of apple rootstock">clonal rootstocks of apple increases by 2–3 times compared to the vertical method. However, such layers turn out to be less vigorous, and some of them have to be grown further in beds during the following year. The method is mainly used for accelerated propagation of clonal rootstocks.

Sequence of work for trench layering propagation:

1. In spring, one-year-old ripened branches are shortened by 1/4 of their length.
2. They are placed horizontally in furrows 5–8 cm deep and secured with wooden hooks or metal staples.
3. When vertical shoots reach a height of 10–15 cm, they are hilled with moist soil by 5 cm.
4. As the shoots grow, hilling is repeated 2–3 times, forming a ridge up to 20 cm high.
5. In autumn, the mother branch is cut into pieces along with the rooted shoots.

Air layering is used to a limited extent on an industrial scale due to the relatively low yield of nursery plants. The essence of the method consists of rooting the stem part of a shoot without detaching it from the mother plant. To do this, the stem is girdled or wounded, wrapped in moist moss, and covered with film to prevent drying out. At the end of the growing season, the shoot with adventitious roots is separated from the parent plant and sent for further growing.

Physiology and methods of stimulating root formation

Successful rooting of layers depends on creating conditions that stimulate rapid cell division and the initiation of root primordia. An agronomist can artificially accelerate this process by influencing the distribution of nutrients and the anatomy of the shoot. The main task is to block the outflow of assimilates without disrupting the supply of water and mineral elements to the branch.

To accumulate plastic substances in the rooting zone, phloem girdling or changing the inclination of the branches is used. In this case, the xylem must remain undamaged so that water continues to flow into the layer without hindrance. An excess of photosynthesis products in the bark damage zone intensifies the formation of adventitious roots.

Shading (etiolation) of the rooting zone restructures the stem. Without access to light, cambium activity is activated, bark tissues expand, and root primordia in the cambial zone are initiated significantly faster. Additionally, rooting is increased by treatment with synthetic auxin preparations in combination with etiolation and wounding.