Asexual Reproduction in Plants Vegetative Propagation

Contents Definition Modified Stems Modified Roots Modified Leaves Modified Buds Sexual Vs Asexual Reproduction Vegetative Propagation Cuttings Grafting Layering Budding Micropropagation (Tissue Culture) Cloning

Definition asexual reproduction: does not involve the manufacture or union of sex cells or gametes e.g. binary fission, fragmentation, spore formation and budding - involves only one parent and offspring are genetically identical (have the same genetic content) to parent.

What happens? Part of the plant becomes separated from the parent plant and grows into a new plant. New plants generally develop from an axillary bud of the parent plant. Parts of the parent plant are specially modified for the purpose.

Modified Stems Runners: horizontal running over the soil surface - terminal bud of the runner sends up new shoots e.g. strawberry, creeping buttercup. Stem Tubers: swollen underground stem tip - buds (eyes) produce new shoots e.g. potato

Runners e.g. strawberries

Stem tubers e.g. potatoes

Modified Roots Root Tuber: swollen fibrous roots — no eyes (buds) e.g. dahlia, lesser celandine Note: Tap Root: swollen roots for food storage - not a reproductive organ - biennial plants e.g. carrot, turnip

Root tuber e.g. dahlia

Modified Leaves Some plants produce plantlets along the edges of the leaves. Plantlets reach a certain size, fall off and grow into new plants e.g. Bryophyllum (mother of thousands)

Bryophyllum with plantlets

Modified Buds Bulbs: swollen underground bud with fleshy leaves and reduced stem e.g. daffodil, onion, tulip

An onion bulb

Bulb – swollen leaves on a flat stem

Sexual (Seed) Vs Asexual (Vegetative) Reproduction (1/2) Cross pollination ensures variation More resistant to disease. Dispersal reduces competition. Seeds can remain dormant and survive unfavourable conditions Sexual reproduction favours evolution Sure of establishing new daughter plant New plants well developed before separating from parent Retain parental genotype. New plants obtained in a shorter time. Only one parent needed.

Sexual Vs Asexual Reproduction (2/2) Seed production - complex. A lot of seed produced - few new plants obtained. Pollination + dispersal depend on external agents. Seeds + fruits eaten by animals Grow in clumps - competition for minerals, light, space. Susceptible to disease - all genetically similar - clones

Vegetative propagation vegetative propagation: reproduction not involving seed Two types: Natural e.g. rhizomes, corms, tubers, bulbs, Artificial - used by gardeners to propagate plants e.g. cuttings, layering, grafting, and budding.

Cuttings cutting: slip removed from plant and rooted in water or well-watered compost e.g. busy lizzie, geranium.

Grafting grafting: method of plant propagation where the scion (i.e. the plant to be propagated) is attached to the stock (i.e. the plant onto which it is grafted) e.g. apple trees.

Layering layering: method of artificial / vegetative propagation where a branch of a plant is bent over and pinned to the earth at a node. When roots develop the branch is separated from the parent plant. Useful for the propagation of woody plants e.g. blackberry, gooseberry.

Budding budding: a method of plant propagation where a bud (of a rose) is attached to the stock (of a briar) e.g. roses.

Micropropagation (Tissue Culture) (1/2) Cells removed from a plant or animal and grown as a tissue culture in a special culture medium. An entire plant can be grown from a small piece of stem, leaf or root tissue. Once the tissue develops into a plantlet it can be divided up again to produce many identical plants. Used in mass production of house plants and crops such as bananas, strawberries and oil palm trees.

Micropropagation (Tissue Culture) (2/2) Provides a larger number of plants more quickly than cuttings. Can be used to check cells for a particular feature e.g. resistance to chemicals or a particular disease.

Tissue culture in the laboratory

Micropropagation of oil palm trees

Cloning clone: all offspring genetically identical - produced asexually i.e. all have come from one original parent e.g. King Edward potato. Clones are produced by mitosis. All the offspring from the various methods of vegetative reproduction (both natural and artificial) mentioned above are examples of clones.

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