Plant Propagation • Use of specialized stems, roots and leaves
Reasons for Asexual Reproduction • 1. Fixes superior genotypes • Heterozygous verses Homozygous genotype • Dominant verses Recessive • Complete dominance verses Incomplete dominance
2. Uniformity of population • Plant size • Growth rate • Flowers • Harvesting will be uniform • 3. Facilitating propagation • Easier to propagate vegetatively than from seeds
4. Shorter time to flowering • Maintains maturity in the plant instead of having to go from the juvenile to the mature stage. • 5. Can combine more than one genotype • Root stock • Dwarfing, semi-dwarfing – standard root stocks, disease and drought and insect tolerance • Scion • Varietal specificity – 5 kind apple tree
6. Control phase of development • Juvenile • Plant cannot flower in this stage –easily propagated • English Ivy • Young citrus have thorns • Transitional – inbetween - Acacia juvenile leaves are pinnately compound – mature are long and thin • Mature – capable of flowering
Air Layering • Done on woody plants • Select a suitable branch • Remove some of the leaves • Wound the branch • Apply rooting hormone • Cover with moist sphagnum moss • Enclose moss with plastic wrap • Keep moist
Specialized Stems and Roots • Geophytes – plants surviving as underground storage organs • Survive • warm/cold conditions in temperate zones • wet/dry conditions in tropical zones • Propagation • by detachable structures called separations • Corms and bulbs • by cutting sections off called divisions • Rhizomes, stems and stem tubers
Structures • Bulbs – short fleshy stem surrounded by thick fleshy scales (leaves) • Outer scales function in food storage • Inner scales act more like leaves • Inside of scales is the vegetative meristem or flowering shoot • Bulblets formed by meristems in axils of scales – when full grown are called offsets • Aerial bublets = bulbils • Underground bulblets = stem bulblets
Types of Bulbs • Tunicate – outer scales become fry and membraneous • Tulip, garlic, onion, daffodile • A. Amaryllis – expanded bases of leaves are used for food storage • B. Tulip – leaves produced on flowering or vegetative shoots • C. Narcissus – has both expanded leaf bases and true scales.
2. Nontunicate bulbs – no enveloping dry cover – scales are separate and attach at the basal plate • Easily damaged if not handled carefully • Roots form midsummer and persist through the next year • Contractile – shorten and pull the bulb to given level in the ground • Droppers – stolon-like structures growing from the bulb and produce a bulb at the tip.
Growth Stages of Bulbs • Vegetative – roots, stems and leaves • Reproduction – • Induction & flower initiation • Differentiation of flowering parts • Elongation of flowering parts • Anthesis (flowering)
Time of Bloom • Spring Flowering • Tulips flower, the bulb disintegrates while replaced by bulblets – bulblets may or may not be large enough to flower the following year
Daffodils bulbs continue to grow producing offsets that may attain flowering size in a few years.
Flower size and quality are: • Related directly to the size of the bulb • Cool growing conditions favor leaf growth, hence more photosynthates to the bulb increasing its size. • Warm hot conditions result in deterioration of leaves resulting in less energy to the bulb for bulb size increase
Dormant bulbs – the roots disintegrate and the bulb seems dormant. Dig and store in cool dry place • Temperature control of flowering • Moderate temperatures summer and fall result in flower formation • Low but not freezing temperatures promote flower stem elongation • Warming spring temperatures result in flowering
Summer flower bulbs – Lilies • Mother bulb is flower producing • Daughter bulbs are formed by the mother bulb initiated last fall from the scales at the base of the stem axis • Vernalization is the cold period required by the bulb to flower • The flower is formed at the tip of the stem during elongation after the leaves are formed
Scaling – bulb scales are separated from the mother bulb – done midsummer after flowering • Yearling – first year bulbs • Commercials are 3 year old yearlings
Scooping – done with hyacinths by scooping out the bottom of the bulb removing the meristem, the tissue left differentiates into new bulblets
Scoring hyacinths by making a knife score on the bottom of the bulb – bulblets form in the score
Corms • Swollen base of a stem axis enclosed by dry, scale-like leaves • Gladiolus
Tunic – dry leaves that protect the corm • Terminal shoot – apex of stem that develops into leaves and the flowering shoot • Roots – two kinds – fibrous forming from the base of the corm and enlarged contractile roots that develop from the base of the new corm
Storage – corms are dug – not hardy to killing frost – store best at 40 F in moist peat moss • Light – short day blooming – long day vegetative • Cormel produciton favored by shallow planting • New corms favored by deep plantings • Cormels are planted 1-2” deep where grass like foilage forms the first year • Divisions can be done by dividing the corm making sure that there is a bud in each new section
Tubers • Underground swollen stems that are storage structures
Eyes – nodes with small buds above leaf scar. Nodes are spirally arranged • Terminal bud – apical end farthest from the crown of the plant
Apical dominance by the terminal bud occurs • Development of the tuber • New shoots obtain energy from tuber • Tuber then disintegrates • Adventitious roots develop at base of main shoot • Main shoot elongates to soil surface forming lateral buds along the shoot that etiolate horizontally into the soil forming stolons
Stolons elongate during long days periods • Tuberization results from inhibition of terminal growth and cell elongation at the subapical end of the stolon. • Short days lengths and lower night temperatures, low mineral content, increased cytokinins and ABA and reduced gibberellins induce tuberization • Tuber size is influenced by the amount of photosynthates available from the leaves • Suberizaton is necessary to prevent drying out and disease infections.
Tuberous Roots • Sweet potato
Rhizomes • Main stem axis grow horizontally slightly below the soil surface Iris