Plant Seeds, Seedlings, and Propagation

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Plant Seeds, Seedlings, and Propagation
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Where do plants come from?

• Sexual reproduction
• Fruit and seeds
• Asexual reproduction
• Cuttings
• Runners
• Suckers

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What is a Seed?

• A seed is a PLANT inside a BOX with its LUNCH

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

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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.

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Beans and Peas belong to Dicotyledons
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• 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
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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

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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

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Scarification

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

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Growth inhibiting substances

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

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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

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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.

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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

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National Germplasm Repositories(500,000 seeds
representing 8,000 species)
Urbana, Ill. Corn Germplasm
Aberdeen, Idaho National Small Grains Collection
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Woody Landscape Plant Germplasm
Repository Collection, Maintenance, and
Evaluation
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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

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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

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Plant Propagation

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

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• 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

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Specialized Stems

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

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Micropropagation

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

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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

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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