438 Horticulture Today
Copyright Goodheart-Willcox Co., Inc.
Environmental Conditions
As every plant has exclusive
growth requirements, the environmental
conditions needed during stage 2 depend
on the culture being used and the plant
material being propagated. Technicians
must determine light quantity and quality,
the amount of moisture needed, and the
type and amount of nutrition required
based on the explants’ needs.
When plantlets are ready for transfer
to stage 3, they have shoots and leaves that
are rich in green pigment. The plantlets do
not have any roots in stage 2, Figure 17-11.
Stage 3: Rooting
In stage 3, plants are being prepared for
transplant. The plantlets must develop roots
to absorb water and nutrients once they are
transplanted in soil. In stage 3, the plantlets
are carefully transferred to a sterile rooting
medium containing nutrients and growth
regulators such as cytokinins, cytoninins,
and auxin. These hormones control cell
growth, tissue formation, and ultimately
how plants develop. This medium is often
called the transplant medium as it prepares
the plantlet for potting or planting in soil in
stage 4.
Roots often develop below the surface
of the medium. Sometimes, rhizomes
(underground lateral stems) may appear
and serve as the origin for other roots,
Figure 17-12. Root development in this
stage helps signify when plants are ready
for transplanting to soil. The amount of
time required for plants to develop roots adequate for transplanting varies
(ranging from weeks to months) from species to species.
Stage 4: Acclimatization
In stage 4, plantlets are transferred to a sterile potting medium and
acclimated for the transition to a nonregulated environment. Acclimatization
is the gradual exposure of plants to different environmental conditions. This
process is also known as hardening-off. The primary reason micropropagated
plants must be acclimated is because they have been kept in an ideal
environment and may have poor control of water loss and nutrient uptake.
Did You Know?
If a plantlet is subcultured
in stage 2 every six
weeks, it potentially can
yield anywhere from 5
to 120 plants each time,
or a little less than 1000
each year.
Kitto Studio/Shutterstock.com
Figure 17-11. In stage 2, plantlets are multiplied. The tissue has
no roots and only has stem and leaf tissue.
jaboo2photo/Shutterstock.com
Figure 17-12. A rhizome is an underground or subsurface stem.
The rhizome appears black in micropropagation.