- THE FLORICULTURE VEGETATIVE CUTTING INDUSTRY 151
humidity, and supply little to no water to the substrate (Ecke et al. 2004).
This is achieved by the use of fine mist nozzles that provide small water
droplets.
Rooting hormone is not required for the majority of unrooted cuttings
to achieve nearly 100% rooting success, although difficult- or slow-to-
root species and cultivars are often treated with rooting hormone to
improve the uniformity of root initiation or to improve the rooting per-
centage (Cerveny and Gibson 2005). Examples of species that frequently
receive rooting hormone treatments include: bracteantha, calibrachoa,
crossandra, dahlia, gazania, heliotrope, hibiscus, lobelia, mandevilla,
osteospermum, salvia, and thunbergia. Dipping the stem into a liquid or
powder formulation of IBA is the most common approach. Stem appli-
cation rates of IBA range from 500 to 3000 ppm. Foliar application of
IBA to newly stuck cuttings can also promote rooting, while reducing
the time and labor required for dipping cuttings. Foliar application rates
of IBA range from 50 to 500 ppm. The potassium-salt formulation of IBA
is often used for foliar applications as it is water soluble, and therefore
causes less foliar damage compared to alcohol-soluble formulations (J.E.
Faust unpublished).
The cutting is inserted into the substrate to a depth of 1–2 cm. Cut-
tings that are inserted too deeply may reach the perched water table
that exists in some containers where the substrate is water-saturated
and oxygen-deprived, which will delay root initiation (Gislerod 1983).
Therefore, the cutting should remain just above this saturated region
that remains one-quarter to one-half the depth of the cell (Williams
2006). Once all cuttings have been stuck into the rooting substrate, a
surfactant or wetting agent can be sprayed onto the cuttings to help
improve water contact with the cutting leaves, which improves water
uptake and leaf turgidity.
C. Callusing (Stage 2)
Wound-induced physiological changes immediately begin to occur
once cuttings are excised from the stock plant and this initiates adven-
titious root formation (Hartmann et al. 2002). The initial response is
characterized by the death of outer cells surrounding the wound and the
formation of a necrotic plate. The wound is then sealed with suberin and
the xylem is plugged with gum. The necrotic plate protects the wound
site from pathogens and desiccation. Under the appropriate environ-
mental and cultural conditions, cell differentiation and subsequent cell
division of the living cells behind the necrotic plate begins, and a layer
of callus, comprised of parenchyma cells, forms the wound periderm.