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14 Δεκ 2012 (πριν από 4 χρόνια και 11 μήνες)

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Chapter 5

Plant Propagation

Part 2


Asexual Propagation

1

What is Asexual Propagation?


Plant reproduction using leaves, stems,
and roots


Also called vegetative or cutting


propagation


Cuttings are the most common


form of vegetative propagation


2

Why use vegetative prop?


Offspring are clones


Genetically identical to parents


Preserves unusual and valuable plant traits
that may not pass with seed


Used to reproduce plants that seldom
flower or are sterile


Can be much faster than growing an
equivalent plant by seed

3

VEGETATIVE PROPAGATION

Cuttings


Cuttings

are the most widespread vegetative
propagation method.


Vegetative plant parts such as leaves, stems &
roots

that regenerate missing parts to form new plants.


They are cut from parent plants called stock plants
.


The environment required for growing
cuttings is

the same as for germinating seeds: warmth,
moisture, and a growing medium.

4

VEGETATIVE PROPAGATION

Cuttings


Most parts used for vegetative propagation are taken
from above
-
ground portions of the plant,

and must regenerate roots.


The growing medium will determine whether roots

will form, and their quality.


The main requirement is to drain quickly to admit air to
the rooting area, yet retain some moisture.


There is not one superior rooting medium.


Many combinations of materials are used:


Sand and part peat moss, part perlite, part vermiculite.


Pure vermiculite, pure perlite, and pure sand.

5

Strip trays of Oasis foam (phenolic foam) used for
propagation.

6

Cutting types


outdoor types


Hardwood


May be deciduous or evergreen


Taken when plants are dormant


6
-
10 inches long


Semi
-
hardwood


From deciduous plants in summer


Partially matured wood


3
-
6 inches long


Have leaves so must be protected from drying out


7

Cutting types
-

outdoor


Softwood


Taken in late spring


Most reliable type of outdoor cutting


Herbaceous


Similar to softwood cuttings but from herbaceous
plants


Can be taken and rooted at any time in growing
season


Root


Root pieces must be able to form adventitious buds


Only a few species


Must be taken in early spring while CHO loaded

8

www.uvm.edu/~mstarret/plantprop/chapter10.pps (
Mark C. Starrett,
Associate Professor
University of Vermont)

An outdoor field technique of rooting
hardwood cuttings

9

Semi
-
hardwood
cutting rooted in
Oasis foam

10

Cutting types
-

indoor


Stem tip cuttings


Most common type


2
-
4 inches of a growing stem


Leaf
-
bud


Lower stem sections with leaves
-

taken below tip
cuttings


Slower to root and grow than tip cuttings


Stem section


Lower, leafless stem sections


2
-
3 nodes and laid horizontally in rooting bed

11

Cutting types
-

indoor


Leaf cuttings


May include blade and petiole


Longest time to root


Must produce roots, and buds with limited
photosynthetic ability


African violet, snake plant, fibrous begonia


Propagation procedure varies by genera.

12

Leaf
-
bud cuttings

13

www.uvm.edu/~mstarret/plantprop/chapter10.pps (
Mark C. Starrett,
Associate Professor
University of Vermont)

Leaf cutting of tuberous
begonia

14


Leaves of African

violet &
peperomia

are picked with the

petiole attached.

The leaf is buried in the
rooting medium up to the
blade, and new plants form
at the soil line.

Figure 5
-
16a
African violet leaf cutting.

Image copyright © 2008. Paul Postuma

Ars Informatica. By permission.

15

Rules for cuttings


No flowers or flower buds


At least 1 node near the base


Keep leafy cuttings moist at all times


No leaves below soil line


Remove fallen leaves and diseased cuttings
or parts regularly


Use of a rooting hormone is recommended


Reduced light and humid conditions are
required until rooting

16

Rules for Cuttings


Any leaves that will be covered after the cutting is
stuck into the rooting medium should be removed.


Left on, they rot & provide a breeding ground for disease
organisms.


Leaves that die and drop from the cuttings should

be removed, with whole cuttings that appear dead.


A heat source at the bottom of the rooting chamber
where the roots will be forming will increase the speed
and success of rooting cuttings.


Use of a rooting hormone can increase rooting speed
and success.

17

Rules for Cuttings


Gently tug the rooting cuttings about once per
week to determine whether rooting has occurred.


If it slips out easily, no anchoring roots have formed.


The cutting should be inspected for signs of rotting and,

if still healthy, can be reinserted in the medium.


If the cutting does
not

pull out with gentle tugging, it
may have
roots already.


The plastic lid can be opened partially to accustom
the plants to normal humidity, and removed
entirely after several days.


After 1 week, cuttings can be transplanted to pots.

18

www.uvm.edu/~mstarret/plantprop/chapter10.pps (
Mark C. Starrett,
Associate Professor
University of Vermont)

A simple method for propagating leafy cuttings

19


A humid chamber to minimize transpiration can be
made easily with a light translucent storage box.

Figure 5
-
17
A rooting chamber made from a translucent storage box. Idea supplied by Janie Varley, Vanderbilt,
Tex. Photo by Jennifer Finney Janssen, M.Ed., Jackson County Extension Agent

Family and Consumer Sciences,
Texas AgriLife Extension Service.

Leafy cuttings wilt easily
and once severely wilted
are less likely to root.

Cuttings should be

kept moist after cutting &
before being stuck in the
medium to slow water
loss.

20

Water rooting


Many houseplants and some easy
-
to
-
root
outdoor plants can be rooted in water


Coleus, willow


Oxygen is usually lacking, so be careful


Stem tip cuttings are usually used


Roots do not form root hairs


Transplanting to potting soil requires
hardening
-

off

21

www.uvm.edu/~mstarret/plantprop/chapter10.pps (
Mark C. Starrett,
Associate Professor
University of Vermont)

22

Commercial propagation


Intermittent mist benches


Time clocks or electronic leaf


Bottom heat


Shade


23

www.uvm.edu/~mstarret/plantprop/chapter10.pps (
Mark C. Starrett,
Associate Professor
University of Vermont)

Mist
-
a
-
Matic

electronic leaf

24

Mechanical time switches used
to control intermittent mist

24
-
hour clock used to turn on
repeating timer

Repeating timer with tabs used to
turn mist on at certain intervals
and for varying lengths of time

25


A root
-
zone heating system is often also
used to warm only the bases of the
cuttings to encourage faster and more
reliable rooting of cuttings.

Figure 5
-
20
A Heat
-
A
-
Matic

suitable for use with pots or flats.

Courtesy of Griffin Greenhouse

& Nursery Supplies.

26

Hot water tubing on propagation bench

27

55% shade cloth installed
over propagation area

28

Natural Plant Propagation


Crown Division


Layering


Rhizomes


Stolons/Runners


Suckers/Offsets


Bulbs, Corms, Tubers

29


Crown division

is probably the most common
and reliable home propagation method.

One plant is separated into

two or more pieces, each

with a portion of roots & crown.

Used for herbaceous perennials,
shrubs, & houseplants such as ferns,
asparagus ferns, African

violets, and spider plants.

Figure 5
-
21
Division of a plantain lily into several smaller crowns. Photo by George Taloumis.

30

Runners of Strawberry

Simple layering

31


Suckers

and
offsets

are young
shoots that grow from the roots
or stems of mature plants.

Figure 5
-
24
A snake plant with two

young offsets. Photo by Kirk Zirion.


Functionally similar to rhizomes and
stolons, and found in many shrubs &
houseplants such as bromeliads,
succulents, and cacti.

32


Offsets on cacti are frequently
produced on top of the plant
and can be broken off and
rooted without difficulty.

Figure 5
-
25
A pincushion cactus

with offsets. Photo by Rick Smith.


Suckers from the bases of plants
may or may not have developed
root systems independent from
the parent.


If so, they can be transplanted
directly.


If not, they are treated as

cuttings.

33

Storage
Organs: Bulbs, Corms,
and Tubers


Underground storage organs are produced
by some herbaceous perennials.


A repository of stored carbohydrate, botanically,
these

are modified stems with nodes, buds & modified
leaves.


Lilies, gladiolas, and amaryllis.

34

Storage
Organs: Bulbs, Corms, and
Tubers


Their natural means of vegetative reproduction is
the formation of clones of themselves (called
bulbils
,
cormels
, or
tubers
) around the base of the parent.


These can be broken off and planted in new locations.


Preferably while the plant is dormant.

Figure 5
-
26
Removing a daughter bulb from the mother.


Blooming of storage organs
may take 2 to 3 years after

the year they are produced
because a minimum size

must be reached before
flowering will occur.

35

Other propagation methods


Air layering


Grafting


Budding


Tissue Culture


Genetic Engineering


transgenic plants


B.t
.


Roundup
-
Ready crops


36


Choose where the new
root system is desired…

Figure 5
-
22
Air layer. Photo by the author.



A 1” wide strip of bark should
be cut around the stem & the
bark pulled off.

Girdling removes the phloem

& cambium but not the xylem,

which still translocates water

to the top of the plant.


Place a handful or two

of damp sphagnum

moss over the girdled

area & wrap with plastic.

37

Figure 5
-
22
Air layer. Photo by the author.



Use twist
-
ties or tape to
secure both ends and

seal in moisture.


Place foil over the plastic

if the air layer area will be
exposed to direct sunlight.


To prevent overheating.


In 2 to 3 months, when
several roots with lengths of
2” to 3” have formed,

the air layer can be cut

and transplanted to its

own pot.

38

Grafting
and Budding


Grafting

and
budding

are fairly complex methods of
propagation used for reproducing valuable fruit and
ornamental cultivars in nurseries.


Budding & grafting unite genetically different plants
so they
heal together & function as a single plant.


An amateur who wishes to try should plan ahead and

consult reference books for more in
-
depth information.



Budding transfers a bud of one plant to another
plant that will function as the root system, whereas
grafting attaches a small branch to another plant.


Most frequently combining two cultivars of a species

into one plant that exhibits the best features of each.

39

Chip budding. The scion is reduced to a
single bud which is cut to fit, wrapped
with grafting tape, and allowed to heal.


After it heals the stem above is removed
to direct growth into the new bud

40

Tissue
Culture


Tissue culture
, also called
micropropagation
, is

the propagation of plants from nearly
microscopic portions of parent plants.

Figure 5
-
29
Tissue
-
cultured strawberries. Photo courtesy of Barbara M. Reed, National Clonal Germplasm
Repository, Corvallis, Ore.

Importance of propagation from
virus
-

free parent stock has
come to be appreciated

recently as the detrimental
effects of unrecognized

virus infection have

become known.

41

Tissue
Culture


The technique has two distinct advantages
over traditional propagation:


It enables mass production of a cultivar from an
extremely limited amount of parent stock
, in a
relatively small area.


It enables the propagator to eliminate disease
-
causing viruses from the parent material,
unattainable through the use of pesticides.


And to propagate numerous virus
-
free offspring that

are healthy and vigorous.

42

Tissue
Culture


Tissue culture is not an amateur activity, because it
is nearly impossible to achieve the sterile conditions
necessary.


Tissue
-
cultured plants still in test tubes are sold in
nurseries occasionally as novelty items.


Particularly orchids, which were the main plants tissue
cultured for many years.


The test tube is left sealed and treated as a miniature terrarium.


When the plant outgrows the tube it sometimes

can be transplanted to a pot, though the

process is not always successful.

43

Tissue Culture is the process of taking
a small group of plant cells and
successively getting them to grow lots
of shoots, which are then further
divided, and then rooted.

44

GENETIC ENGINEERING


Genetic engineering

can harness the biological
machinery of bacteria and viruses to…


Manufacture otherwise hard
-
to
-
obtain plant products.


Combat genetically caused diseases.


Improve tolerance of plants to adverses.


Attain other similar commendable goals.


For plant improvement, it changes the genetic
makeup of plants, without breeding or selection.


Its main advantage is that it makes possible the
transfer of genes between completely unrelated
plants or bacteria.


In rare cases, even from animals to plants.

45

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


In commercial horticultural production,
research has centered mainly on
vegetable and fruit crop genetic
engineering.


With a limited amount on flowers and other
crops.


Although genetically engineered crops are
in widespread cultivation, most are not
horticultural.

46

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


Generally, genetic engineering of horticultural
crops has focused on


Imparting disease and pest resistance.


Imparting resistance to herbicides.


Extending the length of product
shelf life
.


Altering color.


In flowers.


Imparting cold
-
temperature resistance.


In strawberries and eucalyptus trees.

47

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


One of the best known genetically engineered
horticultural crops is the ‘Flavr Savr’ tomato.


Engineered to retain a firm texture longer than normal.


Tomatoes destined for fresh eating must be hand
-
harvested to prevent bruising.


Unlike canning tomatoes that can be harvested
mechanically

a less expensive process.


Fresh tomatoes must also be transported quickly and
with careful packaging.


To ensure that they arrive at the supermarket in an
attractive condition, appealing to the buyer.

48

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


The ‘Flavr Savr’ inhibits expression of the
genetic material that causes fruit to soften
when it ripens.


The softening part of ripening is slowed,
although the flavor continues to develop.


This allows mechanical harvesting,
increased transport time, and longer fresh
shelf life in the supermarket.

49

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


A second genetically engineered crop
receiving widespread attention is a
Thompson
Seedless grape
variety
engineered to be virus resistant.


One of the most commonly cultivated table
grapes.


Also a component of blended wines.

50

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


Scientists hope that genetically engineered virus
resistance will reduce the expense of chemicals,
and their entry into the environment.


Because it will no longer

be necessary to spray to

prevent the disease.

At present, only papaya &

squash have been engineered
successfully for virus resistance

and put into field production.

51

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


Some opponents of genetic engineering fear it

could upset the ecosystem in unknown ways.


They feel that the accelerated pace of genetic change
could inundate the environment with bizarre plants,
causing an unstable ecological situation.


Some organic farmers fear a biological pesticide,
which they use to control infestations of worms, will no
longer be effective due to insect resistance as a result
of widespread incorporation in many crops.


Bacillus
thuringiensis
, is the source of genetic

material put into plants to cause their cells to

produce an insect poison.

52

COMMERCIAL APPLICATION OF
GENETIC ENGINEERING


The Environmental Protection Agency (EPA)
has approved a number of genetically
engineered plants.


Over 3 million acres of genetically engineered
corn, cotton
, and potatoes were planted in the
U.S. in 1997.


A class
-
action suit has been filed against the
EPA by thirty
-
one groups who charge that the
EPA has been negligent in its approval of
genetically engineered crops.

53