PLANT PROPAGATIONUS 20556

10 Credits – Internal Assessment

Level 2 Horticulture Science

Contents• Asexual vs sexual Propagation

• Sexual propagation (seed sowing)- overview• Seed structure• Germination• Respiration• Seed requirements• Seed Dormancy• Seed Vigour and Viability• Seed sources

Propagation:DEFN:Plant propagation is the process of creating new plants

Plant propagation can also refer to the artificial or natural dispersal of plants.

Types of Propagation: Things that are not examples of Propagation

Asexual and Sexual Propagation

• Asexual Propagation - using one parent plant to produce a new individual that is a clone (genetically identical)

• Key words: offspring, new individuals, parent plant(s),

• Sexual Propagation – recombination of the genes to produce a new individual that is a genetically different

(also known as sexual reproduction)

In Angiosperms -This always involves flowers and always results in seed.

In Gymnosperms/ ferns and Moses this results in spores

Question – if a plant self pollinates is it sexual or asexual propagation?

Examples of Propagation TechniquesSexual Asexual

Seed LayeringTissue CultureGraftingBuddingStem CuttingsLeaf cuttingsRoot CuttingsBulbsCormsRunnerRhizomesCrown divisionStolons

To have sex or not to have sex?Advantages of Sexual Propagation Advantages of Asexual Propagation

• Relative to many asexual propagation techniques – seed sowing is inexpensive

• Produces large quantities of new plants

• Can easily be mechanised• Is the only method of producing

new varieties (essential for plant breeders)

• Creates genetic variation within a crop aiding with disease and pest control

• Genetic variation adds to landscape contrast and beauty

• Can be stored• Controlled ‘hybridisation; of plants

can give increased ‘hybrid vigour’

• No genetic variation resulting in a more consistent product.

• Bypass the immature phase• Can produce plants that are not

easily propagated from seed

Seed sowing - Contents

To understand seed sowing technique we will be looking at:• Seed structure• Germination• Respiration• Seed requirements• Seed Dormancy• Seed Vigour and Viability

Seed Sowing Menu

• Hybrid vigour

When two varieties of plant are crossed together (sexual propagation) the combining of different genetics results in a plant that is hetrozygous for many genotypes.

This often means that a particular trait receives both of the varieties traits

Seed sowing – seed structureThree parts to a

seed

• Seed coat• Endosperm• Embryo

‘A seed is a plant in a box with it’s lunch’

Seed Sowing Menu

Seed sowing – seed structure• Seed coat -the outer covering of a seed helps protect

the embryo from injury and drying out. Seed coats can be thin and soft as in beans or thick and hard as in walnuts or coconut seeds.

• Endosperm, a temporary food supply, is packed around the embryo in the form of special leaves called cotyledons or seed leaves. These are often the first parts visible when the seed germinates.

• Embryo – the ‘baby’ plant.

Seed Sowing Menu

Two different situations:

• Cotyledon(s) appear above ground as first leaves (seed leaves)

• Cotyledon(s) remain below the ground

Seed sowing – Seed Structure• There are two types of plants that produce seeds:

Monocotyledons

and Dicotyledons

Seed Sowing Menu

Seed Structure

Seed Sowing Menu

Germination

• Starts when the seed begins to absorb water

• Ends when the new plant is able to get all its’ energy from photosynthesis.

Germination – the process

1. The seed absorbs water until it swells and smoothens its exterior wrinkles.

2. Swelling continues until the coat of the seed bursts open.

3. Food stored in cotyledons or endosperm soaks up water and soluble substances dissolve in it.

4. Respiration begins thus energy and raw materials are supplied by food for cell division and growth.

5. A radical appears first and then a pumule.

Respiration• During respiration (in plants and animals) energy is

released from sugar (glucose) by a series of chemical reactions. The sugar is broken down into carbon dioxide and water in a process which uses oxygen.

Respiration in seeds• INPUTS OUTPUTS

Match your list to the following.• Allows seed to swell

and break seed coat• Required for

respiration • Speeds up the

various chemical processes

Seed requirements

• Seeds don’t get re-assessment opportunities. Once they begin to germinate they either survive or die.

• Seeds need the WOW factor to survive (water oxygen, warmth). Soil, light, CO2 are only for ‘grown-up’ seeds

• A seed is a plant in a box with it’s lunch – but no dinner – if a seed is in the packet too long it will run out of lunch and die.

Seed dormancy• Dormant seeds are seeds that are in ‘sleep’ mode waiting

for the correct conditions to begin germination. • These conditions include WOW, but also physiological

changes in the seed that determine when the seed will germinate.• Many seeds will not germinate until they have been exposed to a cold

period (been in the ground over winter). • Other seeds will not germinate until the testa has been damaged (damage

may occur from scratching – exposure to stomach acid – attack form micro organisms in the soil)

• Seed dormancy aids a species' survival by delaying germination so that 'overall germination' is dispersed over time.

Seed Storage and Viability• Germination requirements = WOW• Seed storage needs to get rid of the Ws. i.e.

an environment that is cool and dry!• Why can we not store seeds in a oxygen

free environment?

• Seeds have limited viability (ability to germinate) because in storage they are undertaking respiration and slowly consuming their energy supply.

• For this reason seed packets have expiry dates

Seed vigour• Seed vigour describes the ability of a seed to germinate

quickly. Seed storage and genetics determine seed vigour.

Seed Sources• Commercial retailers

Saving your ownHow to save tomato seeds Video instructions – tomato seeds

Seed swap groups

Check out the seed savers website

End – Sexual Propagation• Back to Main menu