Biology%20of%20Propagation

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Chapter 2

• Biology of Propagation

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Biology of Propagation

• Genetics
• Genotype
• All characteristics controlled by genes
• Phenotype
• Overall appearance and performance
• Includes size, vigor, color, shape, adaptations
• Results from interaction of the genotype with the
  surrounding environment

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Biology of Propagation

• What is a propagule?
• Any plant part used to produce a new plant(s)
• Types
• Seeds, cuttings, layers, buds, scions, bulbs,
  corms, tubers
• In plant propagation, we multiply plants using
  propagules of a specific genotype

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Biology of Propagation

• Genetic control in propagation
• Sporophytic stage vegetative growth through
  mitosis (roots and shoots)
• Gametophytic stage reproductive structures
  (flowers) producing gametes (reproductive cells)
  through meiosis

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Sporophytic stage
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Mitosis
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Interphase
Blood Lily
Early prophase
Late prophase
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Metaphase
Anaphase
Telophase
Resumption of Interphase
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Meristems
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Meristems
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Meristems
Vascular cambium
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Sporophytic/Gametophytic stages
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Sporophytic/Gametophytic stage
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Meiosis (Mi-Oh-Sis)
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Biology of Propagation

• Mitosis
• Asexual reproduction
• Vegetative propagation
• Results in a diploid of chromosomes (2n)
• Example plants in the genus, Prunus, have
  multiples of 8 chromosomes (n)
• Peach and apricot have vegetative cells with 16
  (2n)
• Cherries have vegetative cells with 24 (3n)
• Plums have vegetative cells with 32 (4n)

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Biology of Propagation

• How do plants grow?
• Cell division (mitosis)
• Cell enlargement
• Cell differentiation

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Biology of Propagation

• Mitosis occurs in
• Shoot tip
• 1 increases length
• Root tip

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Biology of Propagation

• Meristem
• Any growing region, typically in the roots or
  shoot tips
• Other instances of mitosis
• Wound healing ( callus)
• Why important to plant propagation?

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Biology of Propagation

• Mitosis is CLONING!
• No change in genotype (genes)
• Progeny are genetic copies of the original plant
• Cuttings are a type of cloning!
• Tissue culture is a type of cloning!
• Mutation
• Genetic changes
• Spontaneous
• Created due to environmental factors

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Biology of Propagation

• Totipotency
• Each living cell has the potential (genetic
  information) to reproduce the entire organism
• Important in tissue culture
• Competency
• Potential of a given cell or tissue to develop in
  a particular way (roots, buds, etc.)
• Determinism
• How committed the cell is to produce specific
  organs (flowers or leaves, etc.)

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Biology of Propagation

• Meiosis (sexual reproduction)
• For seedling propagation
• Gametophytic generation
• Flowers with sperm (in pollen) and egg (ovule)
• Each is haploid

• Meiosis is the process of producing male
• and female gametes

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Biology of Propagation

• Genotype of a seedling determines its
• Morphological appearance
• Physiological characteristics
• Interaction with the environment
• Survival of the fittest

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Biology of Propagation

• Variability in seedlings depends on
• Transfer of genetic material from parents
• Dominance/recessiveness of traits
• Gregor Mendel 1860s
• Charles Darwin (Origin of Species, 1859)
• Plant breeders control genetic variability
• Biotech is specialized type of breeding

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Biology of Propagation

• Genetic engineering and biotechnology
• Combine different kinds of DNA by transformation
  using bacteria
• Agrobacterium tumefaciens
• Agrobacterium rhizogenes
• Or by direct bombardment of cells
• By microscopic gold pellets coated with DNA
• Produces transgenic plants
• Also called recombinant DNA technology

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Crown gall caused by Agrobacterium tumefaciens
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Gene gun
Transformed rice embryos
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Biology of Propagation

• Gene expression
• Based on DNA (genes) to produce plant structures
  and growth patterns
• Are often influenced by the environment

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Biology of Propagation

• Epigenetic
• Differences in development not involving a change
  in DNA
• Formation of specific structures
• (stems, roots, leaves, flowers)
• Developmental cycles
• Seasonal (phenology) leaf coloration, leaf
  abscission
• Life (ontogeny) phase changes from juvenile to
  adult
• Induction of adventitious roots, shoots or embryos

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Biology of Propagation
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Biology of Propagation

• Hormonal control of plant growth development
• Hormone - a naturally occurring chemical in
  plants (endogenous) that regulates growth and
  development

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Biology of Propagation

• Auxins
• Indoleacetic acid (IAA)
• Made in developing leaves
• Moves from top to bottom of plant
• Causes coleoptile bending (light degrades)
• Inhibits lateral (side) buds apical dominance
• Induces roots (adventitious) on cuttings
• Mode-of-action NOT REALLY KNOWN!
• Synthetic auxins (1935)
• IBA indolebutyric acid
• NAA naphthalene acetic acid

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IAA molecule
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Basal movement of auxin in coleoptile
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Basal movement of auxin in coleoptile
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Location of light sensing in shoot tip
This experiment was conducted by Charles Darwin
in 1880
Aluminum cap No bending
Only shoot tip exposed
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Location of light sensing in shoot tip

• What Darwin stated
• we must therefore conclude that some influence
  is transmitted from the tip to the more basal
  regions of the shoot thereby regulating growth
  and inducing curvature
• influence was the first reference to hormonal
  regulation in plants
• influence IAA

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Effects of specific light wavelengths on auxin
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Coleoptile - No Auxin Coleoptile Auxin
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Stimulates adventitious rooting
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Auxin actively transported to basal end of
shootsregardless of orientation
Bamboo shoots Upside-down
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Bean with suppressed axillary buds
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Bean with shoot tip removed
Axillary buds no longer suppressed!
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Shoot tip removed and replaced with a capsule
containing lanolin IAA
Axillary buds suppressed!
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Biology of Propagation

• Cytokinins
• Essential for cell division
• Discovered by Dr. Skoog at Univ. of Wisconsin
• 1944
• Kinetin from autoclaved fish sperm isolated
• Zeatin from corn
• 2iP (isopentenladenine)
• BA (benzyladenine)
• Produced by Rhizobium and Agrobacterium

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Zeatin molecule
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Biology of Propagation

• Ratios important

• Mode-of-action of cytokinins also NOT KNOWN!

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Stimulation of root production
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Stimulation of shoot production
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Callus formed from even balance
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Biology of Propagation

• Gibberellins
• Japanese discovered prior to WWII (early 1940s)
• Discovered on abnormally-tall rice plants
• Caused by a fungus called, Gibberella
• Most active compound is GA3
• Found in seeds
• Controls seed dormancy
• Controls germination
• Transported in xylem and phloem
• Promotes shoot elongation via inc. cell division
  and elongation

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Gibberellic Acid (GA3) molecule
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Dwarf peas response to GA3
GA3 - GA3
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Biology of Propagation

• Abscisic Acid (ABA)
• Naturally occurring
• Growth inhibitor
• Controls dormancy of buds and seeds
• Controls leaf and fruit abscission
• Important in moisture stress in plants
• Regulates stomatal closure
• Regulates water uptake by roots

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Abscisic Acid Molecule
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ABA effects on seed germination
ABA After ABA washed off
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Biology of Propagation

• Ethylene
• A gas
• Causes senescence in flowers
• Causes flower, fruit and leaf abscission
• Can induce flowering
• Can induce adventitious roots
• Can stimulate germination of some seeds
• Is a response to wounding and stress
• Causes ripening and fruit maturation
• Ethephon thinning agent in apples, promotes
  ripening
• Currently work being conducted on ways to block
  the action of this gas

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Ethylene Gas Molecule
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Ethylene important in ripening
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Bromeliad
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Pineapple (Anana cosmosus)
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Biology of Propagation

• Life cycles in plants

• Ontogenetic changes in growth and development
  
• patterns over the life of the plant
• Examples
• Annuals - complete entire life cycle in 1
  growing
• season
• Biennial - complete entire life cycle in 2
  growing
• seasons. 1st year vegetative rosette, 2nd
  year
• flowers and seeds
• Perennial - plants that live more than 2 years
• Herbaceous perennials (bulb, rhizome, crown,
• stolon)
• Woody perennials (woody stems above ground)

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Biology of Propagation

• Seedlings
• Develops from a seed

• Flowering a response to
• Chilling (vernalization)
• Photoperiod (daylength)

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Biology of Propagation

• Another type of ontogenetic aging is
• Phase change (juvenile to adult) cyclophysis
• Maturation when in the adult phase
• Shift from vegetative to reproductive
• Can affect rooting of cuttings
• Juvenile cutting of ivy is easy to root
• Adult cutting is difficult
• Juvenile citrus and black locust have spines
• Mature citrus and black locust lack spines

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Juvenile
Mature
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Stipular spines on juvenile black locust
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Biology of Propagation

• Clonal life cycle
• Vegetative propagules retain their juvenile or
  mature characteristics depending on where on the
  plant they were taken from
• Cone-of-Juvenility

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Cone-of-Juvenility
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Biology of Propagation

• Plant Nomenclature
• Labeling is critical in plant propagation
• Prunus persica L. peach

• Species a population of plants recognized by
• similar traits and which interbreed
• Propagated by seed

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Biology of Propagation

• Cline - continuous variation due to environment
  along the range of a species
• Ecotype - distinct and discontinuous variation
  due to environment

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Cline for Acer rubrum (red maple)
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Pseudotsuga menziesii (Douglas fir)
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Zone 4
Zone 6
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Ecotypes of Pseudotsuga menziesii (Douglas fir)
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Biology of Propagation

• Interspecific hybrid- interbreeding between
  species (rare)
• Prunus x cistena purple-leaf sand cherry
• Parentage
• (Prunus pumila x Prunus cerasifera)

• This hybrid is sterile and many interspecific
• crosses are!

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Prunus pumila (female)
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Prunus cerasifera (male)
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Prunus x cistena (sterile hybrid)
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Prunus x cistena (sterile hybrid)
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Biology of Propagation

• Intergeneric hybrid - interbreeding between
  genera (very rare)
• X Cupressocyparis leylandii
• Parentage
• Cupressus macrocarpa x Chamaecyparis nootkatensis

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• Parentage
• Cupressus macrocarpa

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• Parentage
• Chamaecyparis nootkatensis

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X Cupressocyparis leylandii
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Biology of Propagation

• Interfamilial hybrid- interbreeding between
  families (to date, impossible!)
• However, recently (in 2000), plants of two
  different families were grafted together.
• Cactaceae and Capparaceae

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Biology of Propagation

• Another example
• X Fatshedera lizei
• Parentage
• Fatsia japonica Moseri x Hedera helix
  Hibernica

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Fatsia japonica
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Hedera helix
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X Fatshedera lizeii
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Why??
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Biology of Propagation

• Cultivar a cultivated variety that has
  distinguishing characteristics that make it
  different from the species
• Usually reproduced asexually (clones)
• If reproduced sexually, it must retain the
  distinguishing characteristics (typically done by
  careful breeding in annuals and vegetables)

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Biology of Propagation

• Examples of cultivars include
• Prunus subhirtella Autumnalis
• Prunus subhirtella cv. Autumnalis

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Biology of Propagation

• Legal protection of a cultivar
• Patent 20 years (formerly 17 years)
• Must be vegetatively propagated
• You cannot patent a wild-collected plant but you
  can grow it in cultivation, demonstrate that you
  can propagate it and then you can patent it!
• Trademark protects the name, symbol, logo
  forever. You can collect royalties on plants
  with trademarked names!

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Biology of Propagation

• What you should do when you patent a plant is to
  give it a crazy name
• Rhododendron calendulaceum Ugly
• Then register the trademark name for this plants
  as
• Green and Gold rhododendron