1. Plant propagation
Definition: multiplication of a plant so as to preserve it’s unique trait(s)
Plant biology influences the propagation process in a number of ways

2. Types of plant propagation
Sexual (seed) propagation
Asexual (vegetative) propagation

3. Seed Propagation
Basic category: line - a population of seed-propagated plants in which genetic variability is controlled
Example: Phaseolus vulgaris 'Greencrop' green bean is uniform because it is homozygous
Homozygosity is achieved by self-pollination each generation for 5 to 6 generations

4. Heterozygosity vs. Homozygosity
Garden pea: a diploid, where D = tall and d = short, and
D is dominant to d DD Dd dd
DD (all tall)
1/4 DD (tall)
1/2 Dd (tall)
1/4 dd (short
All dd (short)
DD and dd (homozygous) individuals “breed true”; Dd
(heterozygous) individuals segregate tall and short
progeny

5. How inbreeding “fixes” a traitDd F1
(1/2 homozygous, 1/2 heterozygous) F2
(3/4 homozygous, 1/4 heterozygous) F6
(~96% homozygous seedlings)

6. Vegetative Propagation
Basic category: clone - genetically uniform group of individuals derived originally from a single individual by asexual propagation
Example: Solanum tuberosum 'Russet Burbank' potato is uniform because each plant is a clone of the original (heterozygous) seedling
Uniformity is maintained by cutting tubers into pieces and growing new plants from each piece

7. Why some plants don’t “breed true”
In most cases, a particular combination of genes are required
The probability is low of recreating that combination
For example:
AaBbCcDcEe (5 genes influencing a trait)
If this genotype is self pollinated, the chances of recreating this gene combination in the next generation is: (1/2)5 = 1/32 (1 seedling in 32 will be AaBbCcDdEe)
Individuals required for a 95% probability = 94
Individuals required for a 99% probability = 145

8. Types of horticultural crops
Tree and small fruits
Vegetables (annuals and perennials)
Turfgrasses
Landscape woody plants
Flowering plants (annuals and perennials)

9. Why are some horticultural plants propagated vegetatively and some by seed?
Predictability - how much variation will be present in the seedling progeny?
Cost - seeds are always cheaper, but they may not provide enough uniformity

10. Types of crops that are seed-propagated
Vegetable crops, bedding plants, turfgrass species
Characteristics
short-season (1-2 generations per year)
diploids
natural selfing species or crossers that are easily inbred
seedling progeny are uniform for some trait(s)

11. Types of crops that are vegetatively propagated
Small-fruit and tree-fruit crops, landscape woody plants, foliage plants, flowering perennials, cut-flower crops and some flowering potted plants
Characteristics
Are almost always heterozygous (causing segregation in seedling progeny)
Are often long-season crops
May be sterile
Individual plants are often highly valued

12. Other biological terms/concepts relating to plant propagation
Competency and determinism
The 5 major plant hormones
Plant life cycles and phase changes
Species and cultivar concepts

13. Competency and determinism
Competency - potential for specific development in cells (bud, flower, root)
Determinism - the degree of commitment to a certain pathway of development (i. e., to make a flower, root, or veg. bud)
Relevance to propagation
Development of flowers for seed production
Development of roots for vegetative propagation

14. The 5 major plant hormones, relative to propagation
Auxins - important in rooting processes
Cytokinins - important in shoot induction
Gibberellins - seed development
Abscisic acid - seed maturation, dormancy
Ethylene - fruit ripening, rooting (minor effect)

15. Plant life cycles and phase change
Generalization: annuals, biennials are usually easier (cheaper and/or more practical) to propagate by seed, perennials by vegetative means
Phase change
Juvenile - incapable of flowering, fruiting
Mature - perennials propagated vegetatively will usually flower/fruit precociously

16. Concepts of species, cultivar, and propagation
True species can (usu.) be propagated by seed
The cultivar (cultivated variety) name is added at the end of a scientific name - Lycopersicon esculentum ‘Rutgers’
The scientific name (with or without the cultivar designation) does not describe how the named plant is propagated (sexually or asexually)