Chapter 27: Vegetative propagation Leaving Certificate Biology Higher Level

Asexual Reproduction Asexual reproduction is the making of a new independent organism from one parent Plants can reproduce asexually when conditions for sexual reproduction are unsuitable Plants reproduce asexually by 4 main ways: – Stem – Root – Leaf – Bud

Vegetative Propagation – Stem Stem: – Stems can grow to form a new plant – E.g. Strawberry runners Runners are stems that ‘run’ horizontally across the surface of the soil The runners then form a node whereby the stem sends out a root and a shoot producing a new plant The new plant is genetically identical to parent

Vegetative Propagation – Root Root: – Certain plants form an underground root tuber – Tubers remain dormant over winter thereby enabling plant to survive winter – When conditions improve in spring, new shoots emerge from the buds on the tuber – E.g. Dahlia

Vegetative Propagation – Leaf Leaf: – Some plants (e.g. Kalanchoe) can form completely new independent plants from outgrowths on their leaves – Kalanchoe forms new plantlets on the edges of their leaves which then fall off to produce new plants

Vegetative Propagation – Bud Bud: – Vegetative propagation by buds involves the formation of a bulb underground – A bulb consists of a section of underground stem, swollen leaves and a central apical bud aswell as lateral buds – When conditions improve the apical and lateral bud form new shoots (this is why many daffodils form from one bulb)

Comparison of Reproduction by Seed and Reproduction by Vegetative Propagation Reproduction by seed: – Advantages: Variation amongst offspring Wide dispersal (less competition) Some may resist disease Can remain dormant for years – Disadvantages: Complex Inefficient Slow Reproduction by Vegetative propagation: – Advantages: Simple process Efficient Many offspring can be produced in short period of time – Disadvantages: Lack of variation Overcrowding in local habitat No seeds formed

Artificial Propagation Artificial propagation is used by horticulturists to grow new plants and improve upon existing ones: – Cutting: e.g. busy Lizzy, geranium – Grafting: e.g. roses, apple trees – Layering: e.g. blackberry bushes – Micropropagation (tissue culturing): can be used to produce a plant of interest in the laboratory

Artificial Vegetative Propagation – Cutting Cutting: – Plants that can be artificially propagated include the busy Lizzie and geranium – A cutting is removed from plant and transplanted to special soil that includes rooting powder

Artificial Vegetative Propagation – Grafting Grafting: – Grafting two plants together is used to combine the best qualities of two different plants – e.g. roses and apple trees are example of plants in which grafting improves the quality of the roses and apples – The part of one plant, the scion (shoot system), is removed and attached to the healthy part of another plant, the stock (usually a wild plant with a strong root system)

Artificial Vegetative Propagation – Layering Layering: – Layering involves taking a long branch of the parent plant and bending it down so that part of the branch is under the soil – e.g. blackberry plants, roses and carnations are commonly layered to produce more plants with those desired characteristics, i.e. large flowers

Artificial Vegetative Propagation – Micropropagation Micropropagation: – Micropropagation is tissue culturing of small amounts of plant tissue to produce new plantlets with the desired characteristics of the parent plant – It is an expensive method of propagation but can be very efficient when huge numbers of the particular plant are required