Asexual Reproduction
Methods of Vegetative Propagation
� Cutting
� Grafting and budding
� Layering
� Specialised stems and roots
CuttingCutting
Propagation by Cutting
� Stem cuttings
- hardwood
- semi-hardwood
- softwood
- herbaceous
require only the formation ofa new adventitious rootsystem because a potentialshoot system is alreadypresent
e.g. spruce, pine , juniper, citrus, olive, apple
� Leaf-bud cuttings
� Root cuttings
� Leaf cuttingsmust initiate a new shootsystem as well as a newadventitious root system
e.g. begonia, African violet
e.g. poppy, geranium, horse radish
e.g. blackberry, raspberry, Ficus
� Preformed or latent roots- preformed root initials develop naturally on stems while they are still attached to the parent plant and generally remain dormant until the stems are made into cuttings and placed under favourable environmental conditions
- origin of preformed root initials in stems of woody plants:a. rays (willow, poplar, citrus)b. cambium (apple, juniper)c. leaf and bud gaps
� Wound-induced roots
Adventitious Root Formation
Callus – an irregular mass of
parenchyma cells in various stages
of ligninfication
� Wound-induced roots- develop only after the cutting is made- Phases of wounding response:
a. outer injured cells die; a necrotic plate is formed (protect from pathogens and desiccation); the wound is sealed with suberin; xylem may plug with gum
b. Living cells behind the plate begin to divide; a layer of parenchyma cells form callus which develops into a wound periderm
c. certain cells in the vicinity of vascular cambium and phloem begin to divide and initiate de novo adventitious roots
- origin of wound-induced de novo adventitious roots in stems of woody plants:a. Cambium and raysb. bud and leaf gapc. Pericycled. Calluse. others (resin duct, parenchyma within the inner cortex)
Stages of de novo Adventitious Root Formation
Cells in potential sites
Dedifferentiation:Cells acquire competence
Competent
Determined
Induction
Differentiation
Formation of root initials
Formation of root primordia
Growth and emergence of adventitious roots
Hartmann et al. (2002) Hartmann and Kester’s Plant Propagation – Principles and Practices 7th ed. Prentice Hall, New Jersey, USA.
Flow Diagram of Adventitious Root Formation
Direct root formation Indirect root formation
Callus formation
Undifferentiated cell division
Cell differentiation
Cytological changes
Directed polar cell division
Induced competent root forming cells: potential
root initiation site
Competent root forming cells: potential
root initiation site
Vascular strand formation
No rootsNo roots
Induction-stimulusInduction-stimulus
Root initials
Organization at apex
Root primordium
Differentiation
Vascular connections
Root emergence
Cells in potential sites
Dedifferentiation:Cells acquire competence
Competent
Determined
Induction
Stages of Adventitious Shoot Formation
Differentiation
Formation of meristemoids of adventitious buds
Formation of adventitious buds (embryonic shoots)
Growth and elongation of adventitious buds into adventitious shoots
Hartmann et al. (2002) Hartmann and Kester’s Plant Propagation – Principles and Practices 7th ed. Prentice Hall, New Jersey, USA.
Grafting and BuddingGrafting and Budding
Terminology
� Grafting:
� The union of a root system (understock) with a shoot system (scion) in such a manner that they subsequently grow and develop as one composite plant
� Budding:
� A form of grafting that uses a small scion (e.g. axillary bud)
scion
rootstockaxillary bud)
� Scion:
� A short piece of detached shoot containing several dormant buds which, when united with the rootstock, comprises the upper portion of the graft and from which stem and branches will grow.
� Rootstock (understock or stock):
� The lower portion of the graft, which develops into the root system of the grafted plant
Uses of Grafting and Budding
� To perpetuate clones desired for their fruiting, flowering, orgrowth characteristics that cannot be propagated by otherasexual means
� To provide special characteristics
� To combine more than one scion cultivar on the same plant
� To repair graftage for injuries
� To test for viral diseases
� To study plant development and plant physiology
Types of Grafting
� Detached scion graft
� Apical graft (splice graft/whip graft)
� Side graft
� Bark graft
� Root graft
� Approach graftSplice graft
scion
rootstock
� Approach graft
� Repair graft
� Bridge graft
� inarching
scion rootstock
Inarching
Approach graft
New seedling
Injured
tree
Types of Budding
� Chip budding
� T-budding
� Inverted T incision
Patch budding� Patch budding
� Flute and ring budding
� I-budding
� Microbudding
Chip Budding
Front view Side view
T-Budding
LayeringLayering
Definition
Layering
A vegetative propagation system
whereby adventitious roots are initiated whereby adventitious roots are initiated
on a stem which is still attached to the
mother plant
Types of Layering
� Layering techniques� Simple layering� Compound layering� Serpentine layering� Air layering (marcottage)� Mound layering� Trench layering� Drop layering
Air layering
� Natural layering� Runners: specialised stems that develop from the leaf axil of the
crown and grow horizontally along the ground and form newplants at one of the nodes
� Stolons: specialised underground stems that grow horizontallyfrom the crown
� Offsets: lateral shoots that develop from the base of the mainstem
� Suckers: shoots that arise from adventitious buds on a root� Crowns: root-stem junctures of a plant from which new shoots
are produced
Mound layeringStool shoots
Specialised Stems and RootsSpecialised Stems and Roots
Specialised Vegetative Structures
Bulb
Corm
Tuber
Tuberous stemTuberous stem
Tuberous root
Rhizome
Pseudobulb
Bulbs
A bulb is a specialised underground structure consisting of a short,
fleshy stem axis, bearing an apical flower primordium enclosed by
thick, fleshy scales
Examples: tulip, daffodil, onion, lily
1. De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam, The
Netherlands.
2. http://www.turf.uiuc.edu/NCR-192/turf_midwest/turfgrass_plant.htm
Corms
A corm is a unique geophyte structure in which the swollen base of
the stem axis has distinct nodes and internodes, and is enclosed by
dry, scale-like leaves
1. De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam, The
Netherlands.
2. http://www.turf.uiuc.edu/NCR-192/turf_midwest/turfgrass_plant.htm
Tubers
A tuber is a swollen modified stem with nodes and internodes, which
functions as an underground storage organ
Example: Potato, Caladium
1. De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam, The
Netherlands.
2. http://www.turf.uiuc.edu/NCR-192/turf_midwest/turfgrass_plant.htm
Rhizomes
A rhizome is a fleshy, horizontally growing stem at or just below the
ground surface
1. De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam, The
Netherlands.
2. http://www.turf.uiuc.edu/NCR-192/turf_midwest/turfgrass_plant.htm
Examples: bamboo, sugar cane, banana, iris
Tuberous Roots and Stems
A tuberous root is an enlarged secondary root which functions as a
storage organ
Example: Sweet potato, cassava
A tuberous stem is a swollen stem produced by the enlargement of the
hypocotyl
Example: Begonia
http://www.hort.cornell.edu/4hplants/Vegetables/SweetPotato.html
http://www.ars.usda.gov/is/pr/2005/050711.htm
Pseudobulbs
A pseudobulb is a thickened, fleshy stem made up of one to several
nodes, which functions as a storage organ
Example: orchid
http://www.anbg.gov.au/cpbr/cd-keys/orchidkey/html/genera/glossary.htm
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