Principles of Propagation by Cuttings

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Chapter 9

• Principles of Propagation by Cuttings

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Biology of Propagation by Cuttings

• Labor costs up to 80 of cost of propagation
• The biology of what actually triggers
  adventitious root formation is largely unknown!

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Biology of Propagation by Cuttings

• Adventitious root bud formation
• Stem and leaf-bud cuttings only need to produce
  adventitious roots
• Root and leaf cuttings need to develop both
  adventitious buds adventitious roots

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Biology of Propagation by Cuttings

• Dedifferentiation - the ability of previously
  developed, differentiated cells to initiate cell
  divisions form new meristems adventitious
  roots and buds

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Biology of Propagation by Cuttings

• Adventitious root formation (natural)
• Corn brace roots

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Biology of Propagation by Cuttings

• Adventitious root formation (natural)
• Dracena or Ficus aerial roots

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Biology of Propagation by Cuttings

• Adventitious root formation (natural)
• 2 types
• 1.) Preformed (latent) root initials - develop
  naturally on the stem and lie dormant
• Ex willow, hydrangea, poplar, coleus, marigold,
  tomato, Swedish ivy, pothos
• 2.) Wound-induced roots - develop only after the
  cutting is made in response to wounding. Formed
  de novo ( anew)

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Preformed root initials-Coleus
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Preformed root initials-Pothos
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Preformed root initials-Swedish Ivy
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Preformed root initials-tomato
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Preformed root initials-willow
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Biology of Propagation by Cuttings

• Order of events to produce wound-induced roots
• 1.) outer, injured cells die
• 2.) a necrotic plate forms and seals the wound
  (suberin) cork and gum blocks xylem
• 3.) parenchyma cells (callus) form behind plate
• 4.) cells near the vascular cambium divide and
  produce adventitious roots

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Biology of Propagation by Cuttings

• Exact location of origin of adventitious roots
  (still unclear!)
• Herbaceous plants originate outside and between
  vascular bundles
• Note in carnation, roots hit fiber sheath in
  stem and cannot penetrate and must grow down
  through stem until they emerge from the base of
  the cutting
• Woody perennials originate from cambium or
  young phloem

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Biology of Propagation by Cuttings

• Direct root formation from vascular tissue
• Indirect root formation from callus
• Difficult-to-root species often have a ring of
  sclerenchyma cells that block root penetration.
• Difficult-to-root species often produce callus
  first and then roots from the callus (Indirect
  root formation)

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Biology of Propagation by Cuttings

• Origin of new shoots and roots in leaf cuttings
  from
• Preformed 1 meristems - cells still meristematic
  (rare)
• Ex piggyback plant, kalanchoe
• Wound-induced 2 meristems - dedifferentiated
  cells
• Ex African violet, begonia

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Biology of Propagation by Cuttings

• Limiting factor in leaf cutting propagation is
  the formation of adventitious buds NOT
  adventitious roots!
• Ex rubber tree leaf roots readily but never
  forms adventitious shoots

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Biology of Propagation by Cuttings

• Root cuttings
• Need to develop adventitious shoots first then
  adventitious roots develop from the adventitious
  shoot
• Works best on plants that sucker
• Ex apples and crabapples (Malus), lindens
  (Tilia), blackberries/raspberries (Rubus)
• Note root cuttings produce adventitious shoots
  from interior tissue. If you have a periclinal
  chimeric plant (i.e. a thornless blackberry),
  if you propagate this plant by root cuttings, you
  will get plants with thorns

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Biology of Propagation by Cuttings

• Polarity of cuttings
• Distal end nearest the shoot tip shoots
• Proximal end nearest the crown (shoot/root
  junction) roots
• Note the opposite occurs on root cuttings
• Distal roots
• Proximal shoots
• Polar movement of auxin is an ACTIVE transport
  process (will work against gravity if cutting
  inverted)

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Biology of Propagation by Cuttings

• Hormonal control of adventitious root bud
  formation
• Specific root-forming factor discovered by Went
  in 1929, called, rhizocaline
• Buds effect rooting!
• No buds or dormant buds either inhibit rooting or
  have no effect
• Leaves effect rooting!
• Presence of leaves increases rooting

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Biology of Propagation by Cuttings

• Auxins
• IAA - naturally occurring (identified in 1935)
• IBA
• NAA
• Exogenous IBA or NAA increases endogenous IAA or
  increases tissue sensitivity to IAA

synthetic
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Biology of Propagation by Cuttings

• Root initiation has two stages
• 1.) root initiation
• A.) auxin-active auxin is required for root
  formation
• B.) auxin-inactive auxin not required for roots
• 2.) Root elongation - auxin not required

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Biology of Propagation by Cuttings

• Cytokinins
• zeatin, kinetin, 2iP, TDZ, BA or BAP
• High auxin/low cytokinin ratio favors
  adventitious rooting
• Low auxin/high cytokinin ratio favors
  adventitious buds/shoots
• Difficult-to-root plants often have HIGH
  cytokinin levels

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Biology of Propagation by Cuttings

• Gibberellins
• GA (Japan, 1939)
• Causes stem elongation
• Inhibits adventitious root formation (may block
  protein production) but depends on the stage of
  rooting
• Ethylene and Abscisic Acid produce variable
  responses.

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Biology of Propagation by Cuttings

• Other compounds
• Salicylate phytohormone (contains salicylic
  acid active ingredient in aspirin) from Salix
• Growth retardants/inhibitors
• Ancymidal Arrest
• Paclobutrazol Bonzi
• Uniconazole
• Enhance rooting by acting against GA
• Reduce shoot growth, therefore less competition
  against root production
• None used commercial to improve rooting

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Biology of Propagation by Cuttings

• Classification of plant rooting responses
• 1.) Plant has all the essential endogenous
  substances including auxin. When given proper
  environmental conditions, roots will form
• 2.) Plant has all the essential endogenous
  substances EXCEPT auxin is limiting. Exogenous
  auxin application will cause rooting, given
  proper environmental conditions
• 3.) Some endogenous substances are limiting other
  than auxin, therefore external application of
  auxin has little response

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Biology of Propagation by Cuttings

• Factors affecting regeneration of plants from
  cuttings
• Selection and maintenance of stock plants
  (for cuttings)
• Select material that is easy to root
  (physiologically juvenile)
• Rejuvenate stock material by serial grafting,
  hedging or micropropagation (serial culturing)
• Cone of juvenility (oak and beech leaf retention
  is an indicator of more juvenile areas)

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Fagus sylvatica (beech)
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Biology of Propagation by Cuttings

• Manipulate the environmental conditions and
  physiological status of the stock plant
• Water status take cuttings in the morning when
  plant material is turgid
• Temperature Higher temperatures (54-80F)
  better for rooting (however, only a minor role)

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Primrose
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Biology of Propagation by Cuttings

• Light photoperiod/irradiance/quality
  specifically as they influence CHOs
  accumulation. If photoperiod stimulates floral
  development, this will reduce rooting
  (photomorphogenic response)
• Etiolation of stock plants exclusion of light
• Banding on stock plants localized light
  exclusion (Velcro)
• Shading growing stock plants under reduced
  light conditions. Reduces the production of
  lignins and phenolic metabolites normally used to
  make lignins instead are used to make roots

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Biology of Propagation by Cuttings

• Girdling - constricting the stem, blocking
  downward translocation of CHOs, hormones, etc.
  Good on sweetgum, sycamore, pine
• Girdling and etiolation best for rooting apples

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Biology of Propagation by Cuttings

• CO2 enrichment mixed responses but if
  photosynthesis increases, then increase in CHOs
  which helps supply developing roots with energy.
• CHOs do NOT regulate rooting but provide
  developing roots with energy. A high C/low N
  ratio favors root production over shoot production

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Biology of Propagation by Cuttings

• Note for hardwood cuttings, it is best to
  select slow-growing lateral shoots over
  fast-growing terminal shoots

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Biology of Propagation by Cuttings

• Selection of shoots
• Lateral vs. Terminal shoots
• For softwood cuttings, chose terminal shoots
• For semi-hardwood cuttings, chose lateral shoots
• Basal portion of a shoot best
• More physiologically juvenile
• More preformed root initials

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Biology of Propagation by Cuttings

• Flowering vs. Vegetative shoots
• If easily rooted, it does not matter
• If difficult to root, select vegetative shoots

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Biology of Propagation by Cuttings

• Seasonal timing
• If deciduous
• Hardwood when dormant
• Softwood after Spring flush
• Semi-hardwood early summer
• If evergreen
• Broad-leaf cutting after a flush completed
  (semi-hardwood) -Spring to fall
• Narrow-leaf hardwood best (late fall through
  winter)

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Biology of Propagation by Cuttings

• If you do research in this area (even as a
  nurseryperson), you should reports finding based
  on PHYSIOLOGICAL characteristics and NOT calendar
  dates!
• Days from budbreak
• Hours of sunlight
• Degree-day chilling or heating units
• Can also use phenology- the art of observing
  life cycle phases or activities of plants (and
  animals)

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Biology of Propagation by Cuttings

• For efficient use of personnel
• Difficult-to-root plants are taken in winter
• Easy-to-root plants are taken in spring and
  summer

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Biology of Propagation by Cuttings

• Treatment of Cuttings
• Storage of cuttings
• Stick immediately or
• mist and hold overnight in a refrigerator
  (40-48F)
• Long-term storage in a refrigerator with high
  humidity ( ethylene inhibitors)
• Long-term duration depends on CHO reserves

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Biology of Propagation by Cuttings

• Auxins
• Middle eastern/European practice - put a grain
  seed in the split end of a cutting.
• Seed releases auxin as it germinates and
  stimulates rooting
• An IBA NAA auxin combination is better than
  either alone
• 2 forms of auxin
• Acid water-insoluble, dissolve in alcohol or
  base (KOH)
• Salt water soluble form (typically a potassium
  salt)
• Bacteria and light destroy natural IAA but not
  IBA or NAA

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Biology of Propagation by Cuttings

• Note early bud-break and shoot growth of rooted
  cuttings is important to overwinter survival of
• Acer (maple)
• Cornus (dogwood)
• Hamamelis (witchazel)
• Magnolia (magnolia)
• Prunus (cherry)
• Rhododendron (rhododendron)
• Stewartia (stewartia)

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Biology of Propagation by Cuttings

• Mineral nutrition of cuttings during rooting
• N required for nucleic acids
• Zn is a precursor to auxin
• Leaching of nutrients
• Mist can severely leach nutrients from leafy
  cuttings
• Easily leached N Mn
• Moderately leached Ca, Mg, S, K
• Slowly leached Fe, Zn, P, Cl

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Biology of Propagation by Cuttings

• Should you add fertilizer to the mist?
• No!
• It will inhibit rooting
• Causes salt build-up or cuttings and equipment
• Increase algae (which reduces aeration and causes
  problems with sanitation)

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Biology of Propagation by Cuttings

• Wounding
• Increases callus (which can yield roots)
• Increases ethylene which promotes adventitious
  root production
• Increases the penetration of exogenous auxins
  into the cutting

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Biology of Propagation by Cuttings

• Manipulation of the environment around cuttings
• Water/humidity
• Minimize transpirational losses
• Water uptake is proportional to the water content
  in the medium
• Xylem/tracheids typically blocked after cut so
  wounding increases diffusion of water into the
  cutting

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Biology of Propagation by Cuttings

• Methods to maintain atmospheric water
• Enclosures (tunnels or coldframes)
• Simple and low-cost
• Problem heat is trapped. Shade the plastic or
  use white poly.
• Best for difficult-to-root species requiring
  extended time for rooting (avoid nutrient
  leaching)
• Contact system
• Lay poly. directly on leafy cuttings after
  watering in

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Biology of Propagation by Cuttings

• Intermittent mist
• Developed in the 1940s
• Lowers air temperature (OK)
• Lowers leaf temperature (OK)
• Lowers medium temperature (not good), so should
  use with bottom heat
• Ex Mist-O-Matic

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Biology of Propagation by Cuttings

• Fog systems
• Maximize humidity
• Water particles stay suspended in air
• Reduces foliage wetting and nutrient leaching
• Reduces disease
• Best on difficult-to-root cuttings
• Helps to acclimate plantlets from tissue culture

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Biology of Propagation by Cuttings

• Temperature
• Optimum 66 - 77F for temperate species
• Optimum 78 - 90F for tropical species
• A 10F drop between day/night is best
• Too high air temps. increase budbreak and
  elongation of new shoots (not good)
• Root initiation is stimulated by inc. temps.
• Bottom heat best for root initiation then remove
  from heat for root development

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Biology of Propagation by Cuttings

• Light (irradiance)
• Low light best for rooting woody plants
  (20-30 W/m2 80 - 120 umol/m2/s)
• Moderate light best for rooting herbaceous plants
  (90-100 W/m2 360 - 400 umol/m2/s)

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Biology of Propagation by Cuttings

• Light (photoperiod)
• Long-days or continuous light is best
• Light (quality)
• More red light than far-red light
• Photosynthesis is not required for root formation
  as long as CHOs are adequate