Asexual ReproductionHartmann et al. (2002) Hartmann and Kester’s Plant Propagation – Principles...

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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