Download No Slide Title

Vegetative (Asexual) Propagation
• Used extensively (in hort) to propagate plants that
aren’t easily propagated by seed
• Kinds of vegetative propagation
–
–
–
–
–
Cuttings
Layering
Tissue culture
Specialized structures (bulbs, etc.)
Grafting and budding
All vegetative propagation methods use a piece of one
plant (propagule) to reproduce another (identical) plant
All plants that are propagated from one original plant are
part of a clone (clonal propagation)
Cuttings are (in general) the easiest, the cheapest, and the
most widely used forms of vegetative propagation
Stem cuttings are the most common type of cutting used
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
Redifferentiation requires:
• Cells competent to form a root meristem (root initial)
• Development of a root initial into a functioning root
(determinism)
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)
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)
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)
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
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 isn’t expected
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”)
Time of adventitious root formation in juvenile and
mature leaf-bud cuttings of Ficus pumila treated with
IBA*
Juveni le
Mature
Anticlinal cell
divisions of ray
parenchyma
Day 4
Day 6
Primordia
Day 6
Day 10
First rooting
Day 7
Day 20
Maximum rooting
Day 14
Day 26
*Davies FT et al. (1982) Amer J Bot 69:804-811.
Callus and rooting
• Callus is an irregular mass of dividing parenchyma
cells
• Relationship to rooting:
– Formation of callus and roots are independent events in easyto-root spp.
– Callus formation is often a precursor to root formation in
hard-to-root spp
From Fig. 9-10, Hartmann 2002
Direct root formation
Indirect root formation
dedifferentiation
callus formation
cell differentiation
vascular strand formation
competent root-forming cells
competent root-forming cells
root initials
From Fig. 9-10, Hartmann 2002
Root Initials
apex organization
Root Primordium
differentiation, vascular
connections
Root Emergence