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
Types of plant propagation • Sexual (seed) propagation • Asexual (vegetative) propagation
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
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
How inbreeding “fixes” a trait Dd F1 (1/2 homozygous, 1/2 heterozygous) F2 (3/4 homozygous, 1/4 heterozygous) F6 (~96% homozygous seedlings)
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
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
Types of horticultural crops • Tree and small fruits • Vegetables (annuals and perennials) • Turfgrasses • Landscape woody plants • Flowering plants (annuals and perennials)
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
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)
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
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
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
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)
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
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)
