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)