Natural and Artificial Cloning of Plants

A clone is a genetically identical copy of an organism, cell or gene. OCR A-Level Biology A specification 6.2.1 (a)–(b) requires you to explain how plants reproduce asexually (naturally and artificially), and to describe the techniques used — from simple cuttings to sophisticated tissue culture — together with their advantages and disadvantages.

Key Definitions:

• Clone — a group of genetically identical organisms or cells produced from a single parent.
• Vegetative propagation — asexual reproduction in plants from a vegetative part (stem, root, leaf).
• Cutting — a piece of stem, root or leaf that regenerates into a new plant.
• Grafting — joining tissue from one plant (scion) onto the rooted stock of another.
• Micropropagation / tissue culture — production of many identical plantlets from small samples of plant tissue grown on sterile agar.
• Totipotent — able to differentiate into any cell type, forming a whole new organism.

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Why Clone Plants?

Cloning produces genetically uniform offspring. This is useful when:

• The parent has a desirable genotype (high yield, disease resistance, attractive flowers).
• Sexual reproduction is unreliable (sterile hybrids, difficult seed germination).
• Uniformity is commercially important (orchards, nursery stock, forestry).
• Rare or endangered plants need rapid multiplication.

The main disadvantage is loss of genetic variation: if a disease strikes, all clones are equally vulnerable. This is exactly what destroyed the Gros Michel banana in the 1950s, and now threatens the Cavendish variety that replaced it.

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Natural Cloning: Vegetative Propagation

Many plants reproduce asexually through specialised vegetative structures. The new plant grows from meristematic tissue containing undifferentiated, totipotent cells that can regenerate all plant parts.

Runners (Stolons)

Runners are horizontal stems that grow along the soil surface, producing new plants at each node. Classic examples: strawberry, spider plant, creeping buttercup. A single strawberry plant can produce dozens of daughter plants in a single season.

Bulbs

A bulb is a short underground stem with fleshy scale leaves (modified leaves) that store food. New bulbs form from lateral buds, splitting off as separate plants. Examples: onion, daffodil, tulip, garlic.

Rhizomes

Rhizomes are horizontal underground stems. Buds along the rhizome produce new shoots, and the rhizome itself thickens and branches. Examples: ginger, iris, couch grass, bracken. Bracken can spread across an entire moorland from a single original plant.

Tubers

Tubers are swollen underground stems (or roots) that store food and bear buds ("eyes"). The classic example is the potato: each eye can grow into a new plant. Because tubers are genetically identical to the parent, all commercial potato varieties are essentially clones maintained for decades (e.g. Russet Burbank since 1876).

Suckers

Suckers are shoots that arise from lateral roots of the parent plant, some distance from the main stem. They can establish as independent plants if separated. Examples: raspberry, elm, aspen. A single aspen grove in Utah ("Pando") is a single clone of about 47,000 genetically identical trunks covering 43 hectares — possibly the world's largest organism.

Structure	Type	Examples
Runner (stolon)	Horizontal stem above ground	Strawberry, spider plant
Bulb	Underground stem with fleshy leaves	Onion, tulip, daffodil
Rhizome	Horizontal underground stem	Ginger, iris, couch grass
Tuber	Swollen underground stem	Potato
Sucker	Shoot from lateral root	Raspberry, elm, aspen
Corm	Swollen vertical stem base	Crocus, gladiolus

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Artificial Cloning: Simple Methods

Cuttings

A cutting is a piece of stem, leaf or root removed from a parent plant, which develops roots and grows into a new plant. Gardeners have used cuttings for millennia. The process is straightforward:

1. Cut a length of stem (typically 10–15 cm) just below a node, where rooting hormones are concentrated.
2. Remove lower leaves to reduce water loss.
3. Dip the cut end in rooting powder (contains auxin, usually indole-3-butyric acid) to encourage root formation.
4. Place in moist compost or water.
5. Keep humid until roots form, then pot on.

Advantages: quick, cheap, preserves the exact genotype. Disadvantages: limited number of cuttings per plant, only works with certain species, vulnerable to disease from the parent.

Grafting