PLANT PROPAGATION
Choice of Methods
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Sexual
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Propagation by seed
Asexual (vegetative)
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Cuttings
Grafting
Layering
Division
Propagation Method Distinctions

Sexual
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“True” to seed implies . . .
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–
No characteristics changed
Cultivar termed a Line
Line is homozygous
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Self-pollinated gives progeny like parent
Cereals and vegetables are examples
Other Seed-propagated Cultivars

Inbred lines
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–
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Pure lines, self-pollinated and selected
Used to produce hybrid cultivars
Hybrids
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Example: hybrid corn
Propagation Method Distinctions

Asexual (vegetative)
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–
Necessary when plant is heterozygous
Heterozygous implies:
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Many dissimilar genes
Meiosis segregates/recombines genes
Seed propagation can’t maintain characteristics of
parent
Propagation Method Distinctions

Asexual (cont)
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Used with heterozygous plants
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Piece of vegetative tissue
Suitable environment
“missing parts” develop
Whole plant genetically identical to original
Flower not involved in asexual propagation
Asexual Propagation Facts
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No genetic change (barring mutations)
Heterozygous cultivars carried generations
Cultivars are clones
Numerous methods (see text, Table 14-2)
SEXUAL PROPAGATION
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Seed produced in flower
Meiosis involved
Reduction division yields haploid gametes
Gametes combine in fertilization
Zygote develops into embryo
SEED PRODUCTION

Cultivar preservation
–
Control of seed source essential

If homozygous, self-pollinated . . .
–

purity assured
If homozygous but cross pollinating . . .
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Must separate plants
– Prevent pollen contamination
SEED CERTIFICATION PROGRAM

Government standards
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–
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Isolation
Culling
Inspection
Final seed testing
Harvesting equipment cleaning
CERTIFICATION PROGRAMS (cont)

Four classes of seeds (agronomic crops):
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Breeder seed
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Foundation seed
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White tag; public/private foundation stock
Registered seed

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White tag; plant breeders
Purple tag; progeny of breeder/foundation
Certified seed

Blue tag; sold to farmers; known genetics and purity
Vegetable and Flower seeds

Regulated by seed companies

Seed purity continually tested

Special test gardens
SEED FORMATION

Seed essential parts:
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Embryo

–
Food storage material

–
Develops into new plant
Nourishes embryo; endosperm/cotyledon(s)
Seed coverings

Seed coats/other parts ovary wall
SEED FORMATION (cont)
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Development
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Ovary to Fruit
Ovule to Seed
Integuments to Seed coats
Nucellus to Perisperm
2 polar nuclei/1 sperm to Endosperm (3n)
Egg nucleus/1 sperm to Zygote to Embryo (2n)
SEED STORAGE AND VIABILITY

Some seeds short-lived
–

Others may live many years
–
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Willow, maple, elm
Hard-seeded legumes
Many seeds range between extremes
Often dependent on storage conditions
SEED VIABILITY TESTS
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Cut test
Float
X-ray
Only tell you there is an embryo!
Still don’t tell you the viability!
GERMINATION TEST

% seedlings developing from seeds planted
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–

Use on seeds with no dormancy problems
e.g. flower, vegetable, grain
Several methods
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–
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Moist paper towel (simple)
Plant in seed flats (greenhouse)
Germination chambers (seed-testing labs)
CHEMICAL TEST

Tetrazolium Test
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Living tissue test
Chemical reacts with enzymes in tissue
Color change
Interpretation variable
EXCISED EMBRYO TEST

Used on wood plant species with dormancy
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
Don’t respond in direct germination tests
Embryo cut from seed
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Seed laboratory technique
Moist paper tested in covered dish
Viable embryos show activity (greening)
Non-viable embryos remain white and die
SEED DORMANCY
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Dormancy may allow a seed to resist
germination even though conditions would be
favorable to germinate
Survival mechanism
May require specific techniques to overcome
TYPES OF SEED DORMANCY

Seed coat dormancy
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Impermeable to water and gases (oxygen)
Associated with hard seed coats
Legumes, pine, birch, ash
Natural weathering softens seed coat
Artificial methods:
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Scarification
Heat treatment
Acid scarification
TYPES OF SEED DORMANCY
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Embryo dormancy
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Common in woody perennials
Physiological conditions
Germination blocks in embryo
Break by stratification:
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Chilling temperatures
Moisture
Oxygen
Time
ADDITIONAL DORMANCIES
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Double dormancy; e.g. Redbud
Rudimentary embryos; e.g. Magnolia
Chemical inhibitors:
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–
–

Coumarin
Caffeic acid
e.g. tomatoes, lemons, strawberries
Secondary dormancy; e.g. some woodies
GERMINATION REQUIREMENTS
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Adequate moisture (varies with species)
Proper temperature (varies with species)
Good aeration
Light (some cases)
Free from pathogens
Free from toxic salts
VEGETATIVE PROPAGATION


Asexual – Not involving flowers or fusion of
egg and sperm
Accomplished through mitosis:
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–
–
–

Nucleus contains genetics for entire plant
Cells genetically identical
Cells can still differentiate
Capable of becoming any kind of cell
Due to:
VEGETATIVE PROPAGATION

Totipotency – ability of mature cell to return
to embryonic state and produce whole new
individual
-

Plant cells easy
Many plants use totipotency to self-propagate
Importance – yields genetically identical plant
–
–
Not possible with seed (sexual) reproduction
Meiosis combines genes at random
VEGETATIVE PROPAGATION

Mitosis produces:
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–
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Adventitious roots
Adventitious shoots
Callus
VEGETATIVE PROPAGATION

Used primarily for woody perennials
–
–
Highly heterozygous
Don’t breed true from seed


Desirable characteristics lost
Produces clones
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Fruit, nut, ornamental cultivars
Many are ancient e.g. ‘Thompson Seedless’ grape
Cultivated Clones

Two processes:
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Vegetative propagation of superior seedlings


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Typical method
e.g. ‘Golden Delicious’ apple
Mutations

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Bud sports; e.g. ‘Ruby’ from ‘Thompson Pink’
Chimeras; e.g. variegated pink lemon (fig. 14-10)
Range from slight to serious
–
Depends on where in mitosis and where in plant
Apomixis

Interesting phenomenon
–
Asexual production of seedling from seed
formation in the usual sexual structures of the
flower but without the mingling and segregation of
chromosomes
no union of male and female gametes
–
Seedling characteristics same as maternal parent
–
Propagation by Cuttings

Classified according to part of plant obtained
–
Stem cuttings
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Hardwood
Semi-hardwood
Softwood
herbaceous
Leaf cuttings
Leaf-bud cuttings
Root cuttings
Grafting

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Joining of two separate plant structures
Used on difficult to root plants
Make use of particular rootstock
characteristics
Budding
Grafting and Budding Notes
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Cambial layers of stock and scion must meet
Parts must be held securely
Keep air out!
Union heals by callus production from
parenchyma cells
Adequate temperature for cell division
There are limitations!
Layering
Additional Layering Techniques



Simple layering (like tip layering)
Mound layering
Air layering
Other Plant Structures

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Runners (stolons); e.g. strawberries
Suckers (adventitious shoots); e.g. blackberry
Crowns (used in division)
Specialized stems and roots
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–
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Bulbs
Corms
Tubers
- Tuberous roots
- Rhizomes
Tissue Culture

Micropropagation
–
–
–
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Utilizes small ‘explants’
Callus formation
Cell differentiation
First used on ferns, orchids and carnations