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Sexual propagation = production of new plants using seeds (or spores for ferns) PowerPoint Presentation
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Sexual propagation = production of new plants using seeds (or spores for ferns) - PowerPoint PPT Presentation


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Sexual Propagation. Sexual propagation = production of new plants using seeds (or spores for ferns) . Why propagate with seeds?. Easier, less expensive for some plants. Easier to ship and store. Some plants extremely difficult to propagate asexually.

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slide1

Sexual Propagation

  • Sexualpropagation = production of new plants using seeds (or spores for ferns)
  • Why propagate with seeds?
  • Easier, less expensive for some plants
  • Easier to ship and store
  • Some plants extremely difficult to propagate asexually
  • Invigorate declining performance of a plant line propagated asexually
slide2

Sexual Propagation

  • Seed storage
  • How should I care for the seeds I purchase?
  • Most seeds should be stored in dry, cool conditions
  • In general, 10% decrease in moisture doubles life of seeds
  • In general, 10% drop in temperature doubles life of seeds
  • Some seeds must be stored in moist, refrigerated conditions until planting in Spring (e.g. many native wildflowers in this area)
slide3

Sexual Propagation

  • Seed viability
  • How should I care for the seeds I purchase?
  • If seeds stored more than a year or two, you may wish to check viability (measure of potential to germinate)
  • Seed viability easily evaluated with tetrazolium (TZ) test
  • dry seeds cut to expose the embryo
  • tetrazolium chloride (colorless dye) applied to the embryo
  • After 30 minutes, seeds examined for the appearance of a red color, indicating respiratory activity
  • % of seed with red color is % viability (rarely printed on seed packages)
slide4

Sexual Propagation

  • Seed germination
  • How should I care for the seeds I purchase?
  • If seeds stored more than a year or two, you may wish to measure germination rate directly
  • Seed germination easily evaluated with petri dish test
  • small sample (10-20) from a seed lot placed in conditions
  • often seeds placed on moist filter paper in petri dishes and placed in environmental chamber
  • % of the sample that germinates measure of seed germination (often shown on a seed label )
slide5

Sexual Propagation

  • Seed germination
  • How should I care for the seeds I purchase?
  • Germination = resumption of growth and development of a seed or spore
  • Basic steps necessary for germination:
  • Seed absorbs water (imbibition) and obtains Oxygen to resume metabolic activity
  • Environmental signal breaks dormancy
  • Hormone signal used to stimulate production of enzyme to break down food reserves
  • Food reserves in endosperm or cotyledon used for rapid growth of seedling; first in radicle (root) then in plumule (shoot)
slide6

Sexual Propagation

  • Germination and early growth of seedlings
  • How should I care for the seeds I purchase?
  • Smaller seeds have less stored food than larger seeds
  • Rule-of-thumb: cover seeds with soil at depth of 3x seed diameter
slide7

Sexual Propagation

  • Seed dormancy
  • How should I care for the seeds I purchase?
  • Often need pre-germination treatment to break dormancy
  • Germination inhibited by seeds own physiology or anatomy
  • Dormancy an adaptation for surviving stressful conditions
  • Primarydormancy = dormancy occurs automatically after seed matures (or is harvested)
  • Secondarydormancy = dormancy induced after environmental stress
slide8

Sexual Propagation

  • Seed dormancy
  • How should I care for the seeds I purchase?
  • Primary dormancy caused by:
  • Immature embryos in seeds -- require proper after-ripening treatments (often high temperatures) to stimulate embryo development (e.g. most palms)
  • Programmed winter dormancy -- require cold, moist treatment called stratification (e.g. most native wildflowers, apples)
  • Chemical inhibition by fruit tissue -- require seeds are cleaned (e.g. flowering dogwood)
  • Hard seed coverings prevent imbibition and respiration -- requires scarification
slide9

Sexual Propagation

  • Seed dormancy
  • How should I care for the seeds I purchase?
  • Types of scarification:
  • File seed coat
  • Soak in hot water or acid
  • Exposed to dry heat (fire-adapted seeds)
  • Light may also be important cue to break dormancy (e.g. lettuce and tomato seeds)
  • Lettuce is positively photoblastic
  • Tomato negatively photoblastic
slide10

Sexual Propagation

  • Preparing seedlings for planting
  • How should I care for the seeds I purchase?
  • Seedlings started indoors need to be hardened off before planting
  • Hardeningoff = acclimating the seedlings to new (usually outdoor) conditions
  • Gradually decrease water and fertilizer
  • Gradually decrease temperature
  • Hardening off often done in cold frames