Asexual Reproduction

Transcription

1 Asexual Reproduction

2 Methods of Vegetative Propagation Cutting Grafting and budding Layering Specialised stems and roots

3 Cutting

4 Propagation by Cutting e.g. spruce, pine, juniper, citrus, olive, apple Stem cuttings - hardwood - semi-hardwood - softwood - herbaceous require only the formation of a new adventitious root system because a potential shoot system is already present e.g. blackberry, raspberry, Ficus Leaf-bud cuttings e.g. poppy, geranium, horse radish Root cuttings e.g. begonia, African violet Leaf cuttings must initiate a new shoot system as well as a new adventitious root system

5 Adventitious Root Formation 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 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 rays b. bud and leaf gap c. Pericycle d. Callus e. others (resin duct, parenchyma within the inner cortex)

6 Stages of de novo Adventitious Root Formation Cells in potential sites Competent Determined Dedifferentiation: Cells acquire competence Induction Formation of root initials Differentiation Formation of root primordia Growth and emergence of adventitious roots Hartmann et al. (2002) Hartmann and Kester s Plant Propagation Principles and Practices 7 th ed. Prentice Hall, New Jersey, USA.

7 Flow Diagram of Adventitious Root Formation Direct root formation Indirect root formation Undifferentiated cell division Competent root forming cells: potential root initiation site No roots Induction-stimulus Cytological changes Directed polar cell division Root initials Organization at apex Root primordium Differentiation Vascular connections Root emergence Callus formation Cell differentiation Vascular strand formation Induction-stimulus Induced competent root forming cells: potential root initiation site No roots

8 Stages of Adventitious Shoot Formation Cells in potential sites Competent Determined Dedifferentiation: Cells acquire competence Induction 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 7 th ed. Prentice Hall, New Jersey, USA.

9 Grafting and Budding

10 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 rootstock 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

11 Uses of Grafting and Budding To perpetuate clones desired for their fruiting, flowering, or growth characteristics that cannot be propagated by other asexual 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

12 Types of Grafting Detached scion graft Apical graft (splice graft/whip graft) Side graft Bark graft Root graft Approach graft scion rootstock Splice graft Repair graft Bridge graft inarching Injured tree Inarching scion rootstock Approach graft New seedling

13 Types of Budding Chip budding T-budding Inverted T incision Patch budding Flute and ring budding I-budding Microbudding

14 Chip Budding Front view Side view

15 T-Budding

16 Layering

17 Definition Layering A vegetative propagation system whereby adventitious roots are initiated on a stem which is still attached to the mother plant

18 Types of Layering Layering techniques Simple layering Compound layering Serpentine layering Air layering (marcottage) Mound layering Trench layering Drop layering Air layering Natural layering Mound layering Runners: specialised stems that develop from the leaf axil of the crown and grow horizontally along the ground and form new plants at one of the nodes Stolons: specialised underground stems that grow horizontally from the crown Offsets: lateral shoots that develop from the base of the main stem Suckers: shoots that arise from adventitious buds on a root Crowns: root-stem junctures of a plant from which new shoots are produced Stool shoots

19 Specialised Stems and Roots

20 Specialised Vegetative Structures Bulb Corm Tuber Tuberous stem Tuberous root Rhizome Pseudobulb

21 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.

22 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.

23 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.

24 Rhizomes A rhizome is a fleshy, horizontally growing stem at or just below the ground surface Examples: bamboo, sugar cane, banana, iris 1. De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam, The Netherlands. 2.

25 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

26 Pseudobulbs A pseudobulb is a thickened, fleshy stem made up of one to several nodes, which functions as a storage organ Example: orchid

27 The End of Lecture