Plant Seeds, Seedlings, and Propagation - PowerPoint PPT Presentation

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Plant Seeds, Seedlings, and Propagation

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Radicle - Stem tip developing into a root. Seen once germination has taken place. ... The radicle is encased in the coleorhiza. Seeds are Unique Individuals ... – PowerPoint PPT presentation

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Title: Plant Seeds, Seedlings, and Propagation


1
Plant Seeds, Seedlings, and Propagation
2
Where do plants come from?
  • Sexual reproduction
  • Fruit and seeds
  • Asexual reproduction
  • Cuttings
  • Runners
  • Suckers

3
What is a Seed?
  • A seed is a PLANT inside a BOX with its LUNCH

4
  • Seeds
  • Seed coat
  • Protection
  • Often hard and dry
  • Embryo
  • Plumule
  • Epicotyl
  • Hypocotyl
  • Cotyledon
  • Source of nutrition
  • First seed leaves
  • Begin photosynthesis

5
Seedlings
  • Once the seed has germinated the same 4
    structures become more visible
  • Cotyledons - Food storage organs that function as
    first seed leaves.
  • Epicotyl - Stem above cotyledon. Seen once
    germination has taken place.
  • Hypocotyl - Stem below attachment point. Seen
    once germination has taken place.
  • Radicle - Stem tip developing into a root. Seen
    once germination has taken place.

6
Beans and Peas belong to Dicotyledons
7
  • Cotyledons do not play a significant role
  • Endosperm is the source of nutrition
  • Plumule is encased in a coleoptile
  • The radicle is encased in the coleorhiza

Corn belongs to the Monocotyledons
8
(No Transcript)
9
Seeds are Unique Individuals
  • Seeds are the product of sexual reproduction
  • Each individual is genetically unique
  • Advantage New combinations of traits
  • Disadvantage high variability
  • favorable in nature
  • Unfavorable for agriculture and horticulture

10
Germination
  • Germination is the beginning of seed growth.
  • Seed must be viable.
  • Some require period of dormancy.
  • Brought about by either mechanical or
    physiological circumstances
  • Tough hard seed coats prevent water absorption
  • Some require Scarification
  • Some fruits produce chemical inhibitors of
    germination

11
Scarification
  • In nature wind, water, gravel, rocks, the
    elements scarify seeds
  • Repeated cycles of heat and cold
  • Woody plants of temperate areas
  • Fire
  • Bacteria

12
Growth inhibiting substances
  • Apples, pears, citrus fruits, tomatoes
  • Contain inhibiting substances that prevent the
    seed from germinating within the fruit

13
Germination Favorable Environmental Factors
  • Imbibe water
  • Water activates enzymes that convert starch to
    sugar, proteins to amino acids
  • Presence of oxygen
  • Waterlogged seeds wont germinate
  • Presence or absence of light
  • Varies with the kind of plant

14
Longevity
  • Viability of most seeds is significantly extended
    when the seeds are stored under conditions of low
    temperatures and kept dry.
  • A few species produce seeds with no period of
    dormancy.

15
Seed Banks
  • Seed Banks (in Nature)
  • Are everywhere!
  • Seeds remain buried in the soil until favorable
    environmental conditions allow germination
  • Germplasm Banks
  • USDA stores seeds of every crop variety possible
  • National Plant Germplasm System
  • http//www.ars-grin.gov/npgs/
  • For research
  • To prevent extinction or loss of genes

16
National Germplasm Repositories(500,000 seeds
representing 8,000 species)
Urbana, Ill. Corn Germplasm
Aberdeen, Idaho National Small Grains Collection
17
Woody Landscape Plant Germplasm
Repository Collection, Maintenance, and
Evaluation
18
Asexual Plant Propagation
  • Plants have the ability to produce clones of
    themselves
  • Clones are genetically identical individuals
  • Advantage More of the same is great if the plant
    is healthy and grown in the same environment
  • Disadvantage Bad traits are passed on too. ie
    lack of resistance to pests.
  • Asexual reproduction is a strategy that is used
    by plants in nature as well as in Horticulture

19
Plant Propagation
  • Crown division in Lilies
  • This group of plant represent one clone
  • Each section contains stem and root material
  • Separating them by allows them to reproduce
    further

20
Plant Propagation
  • Cuttings (Horticulture)
  • Propagules (Nature)
  • Sources leaves, roots, stems
  • Wound healing (from the cutting)
  • Development of new organs
  • Must be kept moist!

21
  • Tip Layering (Horticulture)
  • Suckering (Nature)
  • A branch (stem) is bent over until it touches the
    ground
  • Covered with soil
  • New roots develop from the stem

22
Specialized Stems
  • Specialized stems
  • Bulbs
  • Corms
  • Tubers
  • Rhizomes
  • Potatoes are specialized stems called tubers

23
Micropropagation
  • Growing plants in a sterile environment (lab)
  • Can grow large of plants in a small area
  • Explant piece of stem or leaf tissue

24
Micropropagation
  • Tissue is grown in a petri dish
  • Agar
  • Nutrients
  • Growth hormones
  • Shoot formation
  • Microshoots form
  • Subculturing to another medium
  • Theoretically millions of plants can be grown
    from a single tissue sample

25
Micropropagation
  • Commercial micropropagation is performed
    successfully with
  • Orchids
  • Boston Ferns
  • African violets
  • Hostas
  • Apple root stocks help meet market demand
  • Many ornamental woody plants
  • Endangered species
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