Vegetative (Asexual) Propagation

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Vegetative (Asexual) Propagation

• Used extensively (in hort) to propagate plants
  that arent easily propagated by seed
• Kinds of vegetative propagation
• Cuttings
• Layering
• Tissue culture
• Specialized structures (bulbs, etc.)
• Grafting and budding

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All vegetative propagation methods use a piece of
one plant (propagule) to reproduce another
(identical) plantAll plants that are propagated
from one original plant are part of a clone
(clonal propagation)
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Cuttings are (in general) the easiest, the
cheapest, and the most widely used forms of
vegetative propagationStem cuttings are the
most common type of cutting used
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The goal in propagating by stem cuttings is to
replace the missing part (root system)Two
processes are required

• Dedifferentiation - the ability of a
  differentiated cell to initiate cell division
• Redifferentiation - formation of a growing root

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Redifferentiation requires

• Cells competent to form a root meristem (root
  initial)
• Development of a root initial into a functioning
  root (determinism)

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Plants from which stem cuttings can be taken

• Annuals, biennials, herbaceous perennials (most
  are easy-to-root)
• Woodies (range from easy-to-root to hard-to-root)

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Types of rooting on stem cuttings (based on the
type of roots that develop)

• Preformed roots and latent root initials -
  present when the cutting is taken from the stem
• Wound-induced roots - not present when the
  cutting is made (cutting the stem into pieces
  causes a wound reaction that stimulates rooting)

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Preformed roots or latent root initials

• Develop while still attached to the parent plant
• Usually lie dormant till stems are made into
  cuttings
• Are often associated with nodes
• Are common in certain genera (e.g., Salix,
  Hydrangea, Ribes, Populus)

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Wound-induced roots (anatomical events)

• Dedifferentiation - differentiated cells prepare
  to divide
• Formation of root initials from dividing cells
• Root primordia formation - the apex becomes
  organized
• Root emergence through the stem

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Both wound-induced and preformed roots are
adventitious

• New (de novo) growing points (root meristem) form
  on established structures (e.g., a stem)
• Roots arise other than by normal development of
  the seedling
• Or, simply - a root developing where one isnt
  expected

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Origin of adventitious roots in a stem

• Herbaceous near a vascular bundle
• Woodies
• Easy-to-root species (spp.) near the vascular
  cambium directly
• Hard-to-root spp. often requires an intervening
  callus phase (indirectly)

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Time of adventitious root formation in juvenile
and mature leaf-bud cuttings of Ficus pumila
treated with IBA
Davies FT et al. (1982) Amer J Bot 69804-811.
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Callus and rooting

• Callus is an irregular mass of dividing
  parenchyma cells
• Relationship to rooting
• Formation of callus and roots are independent
  events in easy-to-root spp.
• Callus formation is often a precursor to root
  formation in hard-to-root spp

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From Fig. 9-10, Hartmann 2002
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From Fig. 9-10, Hartmann 2002
Root Initials
apex organization
Root Primordium
differentiation, vascular connections
Root Emergence