1. PLANT PROPAGATION

2. Choice of Methods Sexual Asexual (vegetative) Propagation by seed
Cuttings
Grafting
Layering
Division

3. Propagation Method Distinctions
Sexual
“True” to seed implies . . .
No characteristics changed
Cultivar termed a Line
Line is homozygous
Self-pollinated gives progeny like parent
Cereals and vegetables are examples

4. Other Seed-propagated Cultivars
Inbred lines
Pure lines, self-pollinated and selected
Used to produce hybrid cultivars
Hybrids
Example: hybrid corn

5. Propagation Method Distinctions
Asexual (vegetative)
Necessary when plant is heterozygous
Heterozygous implies:
Many dissimilar genes
Meiosis segregates/recombines genes
Seed propagation can’t maintain characteristics of parent

6. Propagation Method Distinctions
Asexual (cont)
Used with heterozygous plants
Piece of vegetative tissue
Suitable environment
“missing parts” develop
Whole plant genetically identical to original
Flower not involved in asexual propagation

7. Asexual Propagation Facts
No genetic change (barring mutations)
Heterozygous cultivars carried generations
Cultivars are clones
Numerous methods (see text, Table 14-2)

8. SEXUAL PROPAGATION Seed produced in flower Meiosis involved
Reduction division yields haploid gametes
Gametes combine in fertilization
Zygote develops into embryo

9. SEED PRODUCTION Cultivar preservation Control of seed source essential
If homozygous, self-pollinated . . .
purity assured
If homozygous but cross pollinating . . .
Must separate plants
Prevent pollen contamination

10. SEED CERTIFICATION PROGRAM
Government standards
Isolation
Culling
Inspection
Final seed testing
Harvesting equipment cleaning

11. CERTIFICATION PROGRAMS (cont)
Four classes of seeds (agronomic crops):
Breeder seed
White tag; plant breeders
Foundation seed
White tag; public/private foundation stock
Registered seed
Purple tag; progeny of breeder/foundation
Certified seed
Blue tag; sold to farmers; known genetics and purity

12. Vegetable and Flower seeds
Regulated by seed companies
Seed purity continually tested
Special test gardens

13. SEED FORMATION Seed essential parts: Embryo Food storage material
Develops into new plant
Food storage material
Nourishes embryo; endosperm/cotyledon(s)
Seed coverings
Seed coats/other parts ovary wall

15. SEED FORMATION (cont) Development Ovary to Fruit Ovule to Seed
Integuments to Seed coats
Nucellus to Perisperm
2 polar nuclei/1 sperm to Endosperm (3n)
Egg nucleus/1 sperm to Zygote to Embryo (2n)

16. SEED STORAGE AND VIABILITY
Some seeds short-lived
Willow, maple, elm
Others may live many years
Hard-seeded legumes
Many seeds range between extremes
Often dependent on storage conditions

17. SEED VIABILITY TESTS Cut test Float X-ray
Only tell you there is an embryo!
Still don’t tell you the viability!

18. GERMINATION TEST % seedlings developing from seeds planted
Use on seeds with no dormancy problems
e.g. flower, vegetable, grain
Several methods
Moist paper towel (simple)
Plant in seed flats (greenhouse)
Germination chambers (seed-testing labs)

19. CHEMICAL TEST Tetrazolium Test Living tissue test
Chemical reacts with enzymes in tissue
Color change
Interpretation variable

20. EXCISED EMBRYO TEST Used on wood plant species with dormancy
Don’t respond in direct germination tests
Embryo cut from seed
Seed laboratory technique
Moist paper tested in covered dish
Viable embryos show activity (greening)
Non-viable embryos remain white and die

21. SEED DORMANCY
Dormancy may allow a seed to resist germination even though conditions would be favorable to germinate
Survival mechanism
May require specific techniques to overcome

22. TYPES OF SEED DORMANCY Seed coat dormancy
Impermeable to water and gases (oxygen)
Associated with hard seed coats
Legumes, pine, birch, ash
Natural weathering softens seed coat
Artificial methods:
Scarification
Heat treatment
Acid scarification

23. TYPES OF SEED DORMANCY Embryo dormancy Common in woody perennials
Physiological conditions
Germination blocks in embryo
Break by stratification:
Chilling temperatures
Moisture
Oxygen
Time

24. ADDITIONAL DORMANCIES
Double dormancy; e.g. Redbud
Rudimentary embryos; e.g. Magnolia
Chemical inhibitors:
Coumarin
Caffeic acid
e.g. tomatoes, lemons, strawberries
Secondary dormancy; e.g. some woodies

25. GERMINATION REQUIREMENTS
Adequate moisture (varies with species)
Proper temperature (varies with species)
Good aeration
Light (some cases)
Free from pathogens
Free from toxic salts

26. VEGETATIVE PROPAGATION
Asexual – Not involving flowers or fusion of egg and sperm
Accomplished through mitosis:
Nucleus contains genetics for entire plant
Cells genetically identical
Cells can still differentiate
Capable of becoming any kind of cell
Due to:

27. VEGETATIVE PROPAGATION
Totipotency – ability of mature cell to return to embryonic state and produce whole new individual
Plant cells easy
Many plants use totipotency to self-propagate
Importance – yields genetically identical plant
Not possible with seed (sexual) reproduction
Meiosis combines genes at random

28. VEGETATIVE PROPAGATION
Mitosis produces:
Adventitious roots
Adventitious shoots
Callus

29. VEGETATIVE PROPAGATION
Used primarily for woody perennials
Highly heterozygous
Don’t breed true from seed
Desirable characteristics lost
Produces clones
Fruit, nut, ornamental cultivars
Many are ancient e.g. ‘Thompson Seedless’ grape

30. Cultivated Clones Two processes:
Vegetative propagation of superior seedlings
Typical method
e.g. ‘Golden Delicious’ apple
Mutations
Bud sports; e.g. ‘Ruby’ from ‘Thompson Pink’
Chimeras; e.g. variegated pink lemon (fig )
Range from slight to serious
Depends on where in mitosis and where in plant

31. Apomixis Interesting phenomenon
Asexual production of seedling from seed formation in the usual sexual structures of the flower but without the mingling and segregation of chromosomes
no union of male and female gametes
Seedling characteristics same as maternal parent

32. Propagation by Cuttings
Classified according to part of plant obtained
Stem cuttings
Hardwood
Semi-hardwood
Softwood
herbaceous
Leaf cuttings
Leaf-bud cuttings
Root cuttings

33. Grafting Joining of two separate plant structures
Used on difficult to root plants
Make use of particular rootstock characteristics

41. Budding

42. Grafting and Budding Notes
Cambial layers of stock and scion must meet
Parts must be held securely
Keep air out!
Union heals by callus production from parenchyma cells
Adequate temperature for cell division
There are limitations!

43. Layering

44. Additional Layering Techniques
Simple layering (like tip layering)
Mound layering
Air layering

45. Other Plant Structures
Runners (stolons); e.g. strawberries
Suckers (adventitious shoots); e.g. blackberry
Crowns (used in division)
Specialized stems and roots
Bulbs - Tuberous roots
Corms - Rhizomes
Tubers

46. Tissue Culture Micropropagation Utilizes small ‘explants’
Callus formation
Cell differentiation
First used on ferns, orchids and carnations