PLANT PROPAGATION

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PLANT PROPAGATION
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Choice of Methods

• Sexual
• Propagation by seed
• Asexual (vegetative)
• Cuttings
• Grafting
• Layering
• Division

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Propagation Method Distinctions

• Sexual
• True to seed implies . . .
• No characteristics changed
• Cultivar termed a Line
• Line is homozygous
• Self-pollinated gives progeny like parent
• Cereals and vegetables are examples

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Other Seed-propagated Cultivars

• Inbred lines
• Pure lines, self-pollinated and selected
• Used to produce hybrid cultivars
• Hybrids
• Example hybrid corn

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Propagation Method Distinctions

• Asexual (vegetative)
• Necessary when plant is heterozygous
• Heterozygous implies
• Many dissimilar genes
• Meiosis segregates/recombines genes
• Seed propagation cant maintain characteristics
  of parent

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Propagation Method Distinctions

• Asexual (cont)
• Used with heterozygous plants
• Piece of vegetative tissue
• Suitable environment
• missing parts develop
• Whole plant genetically identical to original
• Flower not involved in asexual propagation

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Asexual Propagation Facts

• No genetic change (barring mutations)
• Heterozygous cultivars carried generations
• Cultivars are clones
• Numerous methods (see text, Table 5-1)

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SEXUAL PROPAGATION

• Seed produced in flower
• Meiosis involved
• Reduction division yields haploid gametes
• Gametes combine in fertilization
• Zygote develops into embryo

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SEED PRODUCTION

• Cultivar preservation
• Control of seed source essential
• If homozygous, self-pollinated . . .
• purity assured
• If homozygous but cross pollinating . . .
• Must separate plants
• Prevent pollen contamination

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SEED CERTIFICATION PROGRAM

• Government standards
• Isolation
• Culling
• Inspection
• Final seed testing
• Harvesting equipment cleaning

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CERTIFICATION PROGRAMS (cont)

• Four classes of seeds (agronomic crops)
• Breeder seed
• White tag plant breeders
• Foundation seed
• White tag public/private foundation stock
• Registered seed
• Purple tag progeny of breeder/foundation
• Certified seed
• Blue tag sold to farmers known genetics and
  purity

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Vegetable and Flower seeds

• Regulated by seed companies
• Seed purity continually tested
• Special test gardens

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SEED FORMATION

• Seed essential parts
• Embryo
• Develops into new plant
• Food storage material
• Nourishes embryo endosperm/cotyledon(s)
• Seed coverings
• Seed coats/other parts ovary wall

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SEED FORMATION (cont)

• Development
• 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)

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SEED STORAGE AND VIABILITY

• Some seeds short-lived
• Willow, maple, elm
• Others may live many years
• Hard-seeded legumes
• Many seeds range between extremes
• Often dependent on storage conditions

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SEED VIABILITY TESTS

• Cut test
• Float
• X-ray
• Only tell you there is an embryo!
• Still dont tell you the viability!

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GERMINATION TEST

• seedlings developing from seeds planted
• Use on seeds with no dormancy problems
• e.g. flower, vegetable, grain
• Several methods
• Moist paper towel (simple)
• Plant in seed flats (greenhouse)
• Germination chambers (seed-testing labs)

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CHEMICAL TEST

• Tetrazolium Test
• Living tissue test
• Chemical reacts with enzymes in tissue
• Color change
• Interpretation variable

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EXCISED EMBRYO TEST

• Used on wood plant species with dormancy
• Dont respond in direct germination tests
• Embryo cut from seed
• Seed laboratory technique
• Moist paper tested in covered dish
• Viable embryos show activity (greening)
• Non-viable embryos remain white and die

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SEED DORMANCY

• Dormancy may allow a seed to resist germination
  even though conditions would be favorable to
  germinate
• Survival mechanism
• May require specific techniques to overcome

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TYPES OF SEED DORMANCY

• Seed coat dormancy
• Impermeable to water and gases (oxygen)
• Associated with hard seed coats
• Legumes, pine, birch, ash
• Natural weathering softens seed coat
• Artificial methods
• Scarification
• Heat treatment
• Acid scarification

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TYPES OF SEED DORMANCY

• Embryo dormancy
• Common in woody perennials
• Physiological conditions
• Germination blocks in embryo
• Break by stratification
• Chilling temperatures
• Moisture
• Oxygen
• Time

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ADDITIONAL DORMANCIES

• Double dormancy e.g. Redbud
• Rudimentary embryos e.g. Magnolia
• Chemical inhibitors
• Coumarin
• Caffeic acid
• e.g. tomatoes, lemons, strawberries
• Secondary dormancy e.g. some woodies

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GERMINATION REQUIREMENTS

• Adequate moisture (varies with species)
• Proper temperature (varies with species)
• Good aeration
• Light (some cases)
• Free from pathogens
• Free from toxic salts

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VEGETATIVE PROPAGATION

• Asexual Not involving flowers or fusion of
  egg and sperm
• Accomplished through mitosis
• Nucleus contains genetics for entire plant
• Cells genetically identical
• Cells can still differentiate
• Capable of becoming any kind of cell
• Due to

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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

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VEGETATIVE PROPAGATION

• Mitosis produces
• Adventitious roots
• Adventitious shoots
• Callus

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VEGETATIVE PROPAGATION

• Used primarily for woody perennials
• Highly heterozygous
• Dont breed true from seed
• Desirable characteristics lost
• Produces clones
• Fruit, nut, ornamental cultivars
• Many are ancient e.g. Thompson Seedless grape

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Cultivated Clones

• Two processes
• Vegetative propagation of superior seedlings
• Typical method
• e.g. Golden Delicious apple
• Mutations
• Bud sports e.g. Ruby from Thompson Pink
• Chimeras e.g. variegated pink lemon (fig. 5-6)
• Range from slight to serious
• Depends on where in mitosis and where in plant

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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

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Propagation by Cuttings

• Classified according to part of plant obtained
• Stem cuttings
• Hardwood
• Semi-hardwood
• Softwood
• herbaceous
• Leaf cuttings
• Leaf-bud cuttings
• Root cuttings

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Grafting

• Joining of two separate plant structures
• Used on difficult to root plants
• Make use of particular rootstock characteristics

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Budding
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Grafting and Budding Notes

• 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!

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Layering
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Additional Layering Techniques

• Simple layering (like tip layering)
• Mound layering
• Air layering

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Other Plant Structures

• Runners (stolons) e.g. strawberries
• Suckers (adventitious shoots) e.g. blackberry
• Crowns (used in division)
• Specialized stems and roots
• Bulbs - Tuberous roots
• Corms - Rhizomes
• Tubers

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Tissue Culture

• Micropropagation
• Utilizes small explants
• Callus formation
• Cell differentiation
• First used on ferns, orchids and carnations