- THE FLORICULTURE VEGETATIVE CUTTING INDUSTRY 135
produce small-stem-caliper on the cuttings, which can be problematic
since excessively small-stemmed cuttings are difficult for workers to
handle while inserting the cuttings into the propagation medium.
Benzyladenine (BA), a cytokinin, can be used to promote lateral
branching (Svenson 1991; Grossman et al. 2012). Application of ethep-
hon and BA as a tank mix is also done in conjunction with manual
pinching, or in lieu of pinching, to stimulate branching and delay flow-
ering while also reducing stem elongation of plants such as calibra-
choa, cuphea, diascia, lantana (Lantana camara), nemesia (Nemesia
fruticans), petunia, and verbena (J.E. Faust, unpublished).
Gibberellic acid (GA)-synthesis inhibitors are commonly applied to
stock plants to produce cuttings with compact internodes. For example,
paclobutrazol and daminozide can be applied weekly as foliar sprays.
These plant-growth regulators reduce stem elongation and increase the
chlorophyll content of the leaves (Lolaei et al. 2013), both of which are
desirable characteristics for unrooted cuttings.
Tank mixes of GA and BA are applied to stock plants for two differ-
ent purposes. First, stem elongation is promoted for species with exces-
sively compact internodes. The tank mix provides a more desirable
appearance of the developing shoots compared to GA applied alone.
Second, ethylene-induced postharvest leaf yellowing and abscission
are reduced for cuttings when the applications are made prior to har-
vesting the cutting from the stock plant and/or when the application
is made to the cutting immediately after sticking the cutting on the
propagation bench (Currey et al. 2013). Foliar application of GA and/or
cytokinin increases the sink strength of the most mature leaves on the
cuttings. Thus, these leaves retain their carbohydrates and other growth
factors rather than export them to sustain growth in the shoot tip and
to stimulate root growth in the stem base (Currey et al. 2013). Conse-
quently, less leaf chlorosis and abscission occurs on cuttings that have
been pre-treated prior to harvest; however, the increased sink strength
of the mature leaves has a deleterious effect on root initiation, so root-
ing can be delayed (Rapaka et al. 2008). Excessive application of GA or
cytokinin can delay or prevent root initiation in propagation while the
leaves stay green for many weeks. Amongst the synthetic cytokinins,
BA is most useful since the more active cytokinins, such as thidiazuron
(TDZ) and meta-topolin, inhibit root formation too strongly (Mutui et al.
2005; Mutui et al. 2012).
- Cultural Practices.Apex removal, or pinching, is performed
on stock plants to improve branching and to remove shoots that
have matured beyond the proper stage of development for cutting