1. US 20556 10 Credits – Internal Assessment
Level 2 Horticulture Science
Plant Propagation
US 20556
10 Credits – Internal Assessment

2. Contents Asexual vs sexual Propagation
Sexual propagation (seed sowing)- overview
Seed structure
Germination
Respiration
Seed requirements
Seed Dormancy
Seed Vigour and Viability
Seed sources

3. 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

4. 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?

5. Examples of Propagation Techniques
Sexual
Asexual
Seed
Layering
Tissue Culture
Grafting
Budding
Stem Cuttings
Leaf cuttings
Root Cuttings
Bulbs
Corms
Runner
Rhizomes
Crown division
Stolons

6. 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

7. 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

8. 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

9. Seed sowing – seed structure
Three parts to a seed
Seed coat
Endosperm
Embryo
‘A seed is a plant in a box with it’s lunch’
Seed Sowing Menu

10. 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

11. Two different situations:
Cotyledon(s) appear above ground as first leaves (seed leaves)
Cotyledon(s) remain below the ground

12. Seed sowing – Seed Structure
There are two types of plants that produce seeds:
Monocotyledons
and Dicotyledons
Seed Sowing Menu

13. Seed Structure
Seed Sowing Menu

14. Germination Starts when the seed begins to absorb water
Ends when the new plant is able to get all its’ energy from photosynthesis.

15. Germination – the process
The seed absorbs water until it swells and smoothens its exterior wrinkles.
Swelling continues until the coat of the seed bursts open.
Food stored in cotyledons or endosperm soaks up water and soluble substances dissolve in it.
Respiration begins thus energy and raw materials are supplied by food for cell division and growth.
A radical appears first and then a pumule.

16. 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.

17. 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

18. 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.

19. 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.

20. 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

21. Seed vigour
Seed vigour describes the ability of a seed to germinate quickly. Seed storage and genetics determine seed vigour.

22. Seed Sources Commercial retailers Saving your own Seed swap groups
How to save tomato seeds Video instructions – tomato seeds
Seed swap groups
Check out the seed savers website

23. End – Sexual Propagation
Back to Main menu