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Cloning Plants: Horticulture and the
Science
of Plants David Wm. Reed, Instructor |
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BACKGROUND Cloning
Plants Using Vegetative or Asexual Propagation Vegetative or asexual propagation is the
non-sexual reproduction or propagation of a new plant from vegetative
organs (stem, root, leaf).The techniques used are cuttings layering, division, grafting or
budding. We we use cuttings and
layering. The other type of propagation is seed propagation, which is
also called sexual propagation. Asexual
propagation may lead to the formation of a clone. A clone
is defined as a group of plants that were all derived from the same
parent and are propagated solely by asexual (vegetative) means, such as
cuttings, layering, division, grafting or budding. All of the clones
will be identical. An example of a clone would be a group of
plants that were all propagated as cuttings from the same plant. Many
horticultural cultivars were propagated from a single seedling, from a
single mutation that was found as a branch on a plant, or from a
mutation artificially produced by plant breeders or geneticist. Since
all subsequent plants were propagated from this single seedling or
mutated organ, the entire cultivar is a clone. Examples are: ' Cloning Plants and the
Controversy of Cloning Animals Scientist have
only recently learned how to clone animals. The first animal
cloned was Dolly the sheep. Since then many different animals
have been cloned, including cattle, cats, mice and monkeys. It is
rumored that some scientist are even trying to clone people.
Cloning of animals, especially people is
very controversial. However, we have been cloning plants for
centuries and it is very common. That is why when you go to a
garden center, many of the plants look
exactly alike. Propagation by Cuttings A cutting is a stem,
root or leaf that is cut-off the parent plant and placed under
favorable environmental conditions to regenerates new roots and/or
shoots. These new roots and shoots are called adventitious
roots and adventitious shoots. This produces a new
independent plant identical to (or a clone of) the parent. Cuttings are classified based on the plant
part from which they are taken (stem, root or leaf) and their state of
growth (herbaceous, hardwood, etc.). The table on Types of Cuttings shows the different types of
cuttings. Stem cuttings must form adventitious roots (they already
possess shoots), root cuttings must form adventitious shoots (they
already possess roots) and leaf cuttings must form both adventitious
roots and adventitious shoots (they possess neither). Rooting Hormones
Increase Root Formation The cuttings of many plant species will form
adventitious roots readily when placed in a glass or water or under a water mist system. However, the cuttings
of some plant species are very difficult if not impossible to root.
Many of these difficult-to-root plant species can be encouraged to form
roots with the use rooting hormones. See the table below on rooting kormones, which can be purchased at any garden
center. The active ingredient in the rooting hormones is the plant
hormone auxin.
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Protect Cuttings From
Drying-Out When stem and leaf cuttings are removed from the parent plant they are cut-off from their source of water. You must prevent the continued loss of water or many cuttings will desiccate (dry out) and eventually die. For many plants this can be done by placing them in a shaded cool area away from direct sun or spraying the foliage with water several times per day. This is sufficient for hardwood cuttings without leaves and for succulent plants and cacti. Another method is to construct a rooting frame or humidity chamber, which is any box, pot, bench or tray enclosed by a polyethylene (plastic) tent in which the cuttings are placed. The plastic covered humidity chamber cannot be placed in the sun or else it will overhead and kill the cuttings. The best method is to use an intermittent mist system in which a very fine mist of water is automatically and periodically (intermittently) sprayed over the cuttings to decrease both water loss and heat build-up.
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Layering is a propagation technique where roots are
induced to form on a stem prior to the
stem being cut-off from the parent plant. This is contrasted to
cuttings, where roots are formed after the stem is cut-off from the
parent plant. Layering is a common process in nature for many plants,
such as blackberry, ajuga, and strawberry,
which results in their self-propagation. Horticulturists have taken
advantage of this naturally occurring process and have used it for the propagation of many plant species.
Layering is much less of a "shock" to the plant than taking
cuttings. The basic
principle underlying layering is stop the downward movement
of sugars and hormones in the stem by either girdling, ringing,
notching, tying or bending of stems, but at the same time to not stop
the movement of water up stems. Things move down stems in the
tissue called phloem and up stems in the tissue called xylem. We will
demonstrate to you how to cut the phloem but not the xylem. The
table on Types of Layering gives the
various types of layering. . TAKE
HOME LESSONS 1)
To learn how to propagate plants by cuttings. PROCEDURES 1)
How to make cuttings. You will be shown how to take
stem and leaf cuttings from a variety of tropical foliage plants and
garden plants. See the table on Types of
Cuttings which has an image of all the various types of
cuttings. We will only propagate plants that root easily without
needing to be under a water mist system. 2)
How to treat cuttings with rooting powders. You will be shown how to treat the base of the cutting with rooting
powders in order to encourage them to form adventitious roots
better. 3)
How to make an air layer. How to air layer a woody plant will be demonstrated. The table on Types of Layering, which has a picture of an air layer. |
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hardwood
cane 
rhizome 
tuber
root
section 
tuberous root|
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