Transcript Chapter 4

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
An outdoor field technique of rooting
hardwood cuttings
www.uvm.edu/~mstarret/plantprop/chapter10.pps (Mark C. Starrett,
Associate Professor University of Vermont)
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
Leaf cutting of tuberous
begonia
www.uvm.edu/~mstarret/plantprop/chapter10.pps (Mark C. Starrett,
Associate Professor University of Vermont)
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
A simple method for propagating leafy cuttings
www.uvm.edu/~mstarret/plantprop/chapter10.pps (Mark C. Starrett,
Associate Professor University of Vermont)
19
• A humid chamber to minimize transpiration can be
made easily with a light translucent storage box.
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.
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.
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
Mist-a-Matic electronic leaf
www.uvm.edu/~mstarret/plantprop/chapter10.pps (Mark C. Starrett,
Associate Professor University of Vermont)
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.
Used for herbaceous perennials,
shrubs, & houseplants such as ferns,
asparagus ferns, African
violets, and spider plants.
One plant is separated into
two or more pieces, each
with a portion of roots & crown.
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.
Functionally similar to rhizomes and
stolons, and found in many shrubs &
houseplants such as bromeliads,
succulents, and cacti.
Figure 5-24 A snake plant with two
young offsets. Photo by Kirk Zirion.
32
• Offsets on cacti are frequently
produced on top of the plant
and can be broken off and
rooted without difficulty.
• 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.
Figure 5-25 A pincushion cactus
with offsets. Photo by Rick Smith.
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.
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.
Figure 5-26 Removing a daughter bulb from the mother.
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…
– 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.
Figure 5-22 Air layer. Photo by the author.
37
– 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.
Figure 5-22 Air layer. Photo by the author.
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.
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.
Figure 5-29 Tissue-cultured strawberries. Photo courtesy of Barbara M. Reed, National Clonal Germplasm
Repository, Corvallis, Ore.
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 diseasecausing 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 handharvested 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