Transcript Chapter 41: Vegetative Propagation

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: • Reproduction by
Vegetative propagation:
– Advantages:
• Variation amongst
offspring
• Wide dispersal (less
competition)
• Some may resist disease
• Can remain dormant for
years
– Disadvantages:
• Complex
• Inefficient
• Slow
– 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