2.5 Asexual reproduction in plants

Propagation Asexual reproduction: Asexual

reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis

It is used to increase the supply of rare plants

Advantages Only one parent is required and the offspring

is/are a genetic identical to the parent Another name is – vegetative propagation Forms of this include:

Runners Grafts Corms Bulbs Cuttings etc

Lignotubers Is a swelling at the base of a stem that

is a source of dormant buds. Buds are growing points of plants. Underground lignotubers

Lignotubers

Epicormic buds These are buds found under the bark,

which need a form of stimulation in order to grow.

A trigger for growth is usually fire it destroys a chemical that inhibits growth

Epicormic buds

Runners Runners are long stems that grow from

the crown of the plant. They usually grow from a bud near the

soil surface Grasses and strawberries are grown

from runners

Runner pictures and diagrams

Propagation issues (p.105) Commerical propagation of plants need

to overcome the following issues: LENGTH OF TIME: it takes time to grow a

plant that is viable and not susceptible to disease

CARE FOR TRANSPLANTING: horticulturalist’s need to ensure that plants are fully established as transplantation can hinder growth

BALANCE B/W LIGHT AND HEAT: providing light cont. will increase photosynthesis rates which increase growth rates. Yet, too much light can overheat the plants

AVAILABILITY OF PLANT STOCKS: rare plants may cause issues with propagation. If there is a limited stock of parent plants, continuous pruning and tissue removal can cause damage to the parent plant stocks

Benefits of Cloning (p.105)

Cloning allows the commercial propagation of plants that have desirable characteristics. It is also a valuable method of propagation of plants that are difficult to grow from seed

Clones of a plant are very similar in appearance to each other as they are grown from the same organism

Whether they are cloned from the root, stem or leaf they will grow to form an entire new plant

Cont. It is currently a controversial issue due to

the ethical implications of cloning animals and humans

Disadvantages: there are high costs associated with tissue cloning due to the cost, time and labour involved.

It also reduces the genetic variation in a species which may result in survival issues if the environmental conditions change

Tissue culture This only needs only one or a few cells

which give rise to a new plant It is used for plants which are hard to

grow from seeds or seed which are hard to store

Part of the meristematic tissue is taken from the bud of the parent.

Meristematic tissue is from the shoot

Tissue culture – THE STEPS The tissue sample is as small as 1-2mm2

It is soaked in a solution of sodium or calcium hypochlorite for 10 minutes and then washed in distilled water

The tissue is then grown in a nutrient solution until it forms a clump of cells

The clump of cells is cut into smaller pieces and the procedure is repeated several times

The small clumps of unspecialised cells are stimulated to grow into tiny plantlets by the addition of plant hormones.

The plants are removed from the tissue culture flasks and grown the normal way

COPY FIGURE 2.62 from pp. 106