Sexual propagation

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Sexual propagation
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Chap 12. Plant Propagation

• I. Three Methods of Plant Propagation
• Sexual Propagation (Seed Propagation)
• Asexual Propagation (Vegetative Propagation)
• Micropropagation (Tissue Culture)

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Reproductive Biology

• Cell Division
• Somatic cell division (Mitosis)
• Reproductive cell division (Meiosis)
• Flowering and Anthesis
• Megagametogenesis (EMC to Egg Cells)
• Microgametogenesis (PMC to Pollen Grains)
• Pollination and Fertilization
• Pollen germination on stigma
• Pollen tube growth through style tissue
• Double fertilization

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• Mitosis
• - Somatic Cell Division
• Ends up with same number of chromosomes in
  divided cells
• Divided cells are genetically identical to
  maternal cells

2N ---------? 2N 2N
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• Meiosis
• Reproductive cell division
• Undergoes 2 separate divisions
• Forms gametes
• Divided cells have a half of the chromosome
  numbers
• Ends up with genetic re-assortment by
  chromosomal translocation (cross-over)

2N ---?---? N N N N
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Pollen Tetrad and Microgametophyte
  - One tube nucleus    - Two sperm nuclei 
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Megagametophyte

•  
• 1 egg nucleus 
• 2 polar nuclei
•   3 antipodal nuclei
•   2 synergids    

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• Life Cycle
• Alternation of gametophytic (n) and sporophytic
  (2n) stages in a cycle
• Sporophytic (2n) stage is long and gametophytic
  (n) stage is brief

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Double Fertilization
A process of fertilization in which one male
gamete (sperm nucleus, n) unites the egg nucleus
(n) to form embryo (zygote, 2n) and the other
sperm nucleus (n) unites polar nuclei (2n) to
form endosperm (3n)
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Female (left) and Male (right) Flowers of Pumpkin
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Pollination and Fertilization, Angiosperms
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II. Sexual Propagation

• Seed production
• Mostly in conditions
• - - Low humidity (less fungal, bacterial
  diseases)
• - Mild temperature (good for flowering, seed
  set)
• - Even distribution of rainfall throughout year
• - Isolated from major production areas
• Hybrid Seed Production
• - Use of male sterility (US production)
• - Hand pollination (Developing countries)
• Labor Intensive Operation
• - Harvesting, cleaning, and handling

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A Commercial Flower Company
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Flower Seed Production
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Field Drying of Seeds
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Vegetable Cultivar Trials and Seed Extraction
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Seed Cleaning, Drying, and Storing
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Seed Grading, Packaging, Storage
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2. Seed Storage

• Optimum Condition for Seed Storage
• Low temperature (0- -18 oC)
• Low humidity (less than 10 RH)
• Practical Storage Conditions
• 0-10 oC, 50-65 RH
• Seed Longevity Varies by Species
• Most annual flowers last 1-2 years
• Woody plants 5-20 years
• Lotus seed known to last over 1000 years
• Permanent storage at cryogenic temperature(-196
  oC)

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Lotus (Nerumbo nucifera)
Seeds stuck in mud for over 1000 years germinated
well
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3. Seed Germination

• Seed Germination Test
• Seed viability
• Determined by percent germination (100 seed lots)
• Tetrazolium (TTC) test to find tissue viability
• Enhancement of Germination
• Seed quality and storage conditions
• Seed priming to enhance germination vigor and
  uniformity

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Seed StorageNational Germplasm Storage Lab
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Seed Priming

• A process of prehydrating and redrying seeds to
  enhance their subsequent germination performance
• Used for flower and vegetable seeds for uniform
  and vigorous germination

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Germination of Primed Seeds
Irregularities in seed germination, poor quality
seeds
Uniformity in the germination of primed seeds
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Breaking Seed Dormancy

• Scarification
• Overcomes physical seed dormancy
• (Seed coat is impermeable to water)
• Three methods
• Mechanical abrasion
• Hot water (76-100 oC)
• Acid treatment (concentrated sulfuric acid)
• (Seed coat is impermeable to water)
• Stratification
• Overcomes physiological seed dormancy
• (Embryo dormancy, internal dormancy)
• Moistened, cold storage
• Storage at 0 oC for 1-9 months)
• Some species may require warm stratification
• Viburnum, Redbud

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Two Different Types of Germination

• Epigeous Germination
• Cotyledons are exposed above ground
• Epicotyl and hypocotyls are also visible
• Cherry, soybean, radish
• Hypogeous Germination
• Cotyledons are buried in the ground
• Only epicotyl are visible
• Peach, pea, apricot

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Germination of Angiosperm Seeds
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Embryo Culture

• Immature zygotic embryos are excised and
  cultured in vitro to obtain viable seeds
• Used in abortive interspecific crosses (i.e.,
  potato)
• Used for embryos lacking endosperm (i.e.,
  orchids)

Double fertilization
In-ovulo Embryo culture
Seed germination
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Production of Vegetable Seeds
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Onion Seed Production
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Production Herb Seeds
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Field Production of Vegetables
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Seedling Production in Greenhouse
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Plugs to Cell Packs
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Seed Propagation for Trees
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Tissue culture
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Apical Shoot Tip Culture
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Root Induction on Shootlets
Root Induction on Desert Milkweed Left (A) -
Roots are formed on callus due to excess auxin
levels in the medium (undesirable) Right (B) -
Root formation without callusing (desirable)
A
B
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Cloning of Plants by Leaf Disc Culture
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Leaf disc culture of Salpiglossis sinuata
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Clonal Propagation of Orchids
A
B
C
D
A-obtain a meristem explant from a lead, B-an
excised meristem, C- five protocorms formed from
a meristem, D-multiplication of protocorms and
shoot formation
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Mechanical Transplanting of Tissue Culture Grown
Plants
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Tissue Cultured Ferns Grown in Greenhouses
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Staghorn Ferns Grown from Tissue Culture
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Callus Cultures
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Ginseng Root Culture
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In Vitro Production of Cotton Fiber
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