Plant propagation

1
Plant propagation

• Definition multiplication of a plant so as to
  preserve its 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 trait
Dd
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 dont 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)