Sources of seed

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Chapter 6

• Sources of seed

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Sources of seed

• Grass, vegetables flower seeds -produced in
  areas with low summer rainfall, low humidity and
  limited rain during harvest
• Reduces disease
• Sources
• Pacific Northwest, California, South and Central
  America and Australia
• Seed exchanges, collection trips, seed orchards,
  arboreta botanic gardens

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Seed Exchange

• http//www.seedsavers.org/

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• http//www.southernexposure.com/

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Sources of seed

• Harvesting and processing
• Types of fruits
• Dry fruits - most Ag. crops (corn, wheat) do NOT
  dehisce (split-open)

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Sources of seed

• Harvesting and processing
• Types of fruits
• Dry seeds - from fruits that dehisce
• (pods, capsules, cones)

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Sources of seed

• Harvesting and processing
• Types of fruits
• Fleshy fruits - fruits vegetables crops
• (berries, pomes, drupes)

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Sources of seed

• Procedures (dry fruits seeds)
• Drying
• Extraction
• Seed conditioning (sieves for cleaning)
• Procedures (fleshy fruits)
• Extraction -water soak, screen, scoop
• Fermentation - macerate fruit, soak for up to 4
  days _at_ 70F
• (use caution as heat and wet conditions can
  cause germ.)
• Floatation - heavy seed sinks (good), pulp and
  unfilled seeds float (bad)
• Blenderize - cover blades with plastic tubing,
  add water
• Dry immediately (except seeds of recalcitrant
  plants)

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Sources of seed

• Seed testing
• Regulated by State and Federal law
• Seed Act of 1939 (if shipped between states)
• Shipper must provide a label containing
• Name (including cultivars)
• Origin
• Germination
• pure seed
• Other seed included (weed seeds)
• Inert materials (rocks, dirt, etc.)

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Sources of seed

• Sampling
• Composite samples (collected from several bags)
• Submitted sample (what is sent to be tested)
• Working sample (what is actually tested)

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Sources of seed

• Germination tests
• Use 400 seeds
• Divide into lots of 100
• If germination of lots differ by gt10, retest

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Sources of seed

• Blotter or germination papers
• Free from toxins
• Rolled towel test - for cereal grains
• Seed rating
• Normal seed/seedling
• Hard seed - have not absorbed water
• Dormant seed/non-viable - firm and imbibed
• Abnormal seedling - improper shoot/root growth
• Dead/decaying seeds

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Sources of seed

• Excised embryo test
• For woody trees shrubs (because they have a
  long after-ripening period)
• Remove seed coat and endosperm which contain
  germination inhibitors
• Can do on blotters or filter paper
• Provide light
• 64 - 74F

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Sources of seed

• Tetrazolium test (developed in 1949)
• Biochemical method
• 2,3,5-triphenyltetrazolium chloride (TTC) which
  is colorless. Chemical Formula C19H15CIN4
• Living tissue with active dehydrogenase enzyme
  (this removes 2 electrons and a proton from the
  substrate molecule!) to produce formazan (red
  pigment)
• Quick test
• Embryo must be relatively large to see results

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Sources of seed

• X-ray analysis
• Does not test for viability
• Checks for filled seeds
• Checks for insects
• Seeds must be gt 2 mm

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Sources of seed

• Purity tests
• by weight of pure seed present in the sample
• Physically pure (no soil, debris, etc.)
• Genetically pure
• Checked by DNA fingerprinting

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Sources of seed

• Vigor tests
• Not required by law
• Checks for the rapid and uniform emergence and
  development of seedlings under a range of
  environmental conditions

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Sources of seed

• Vigor tests
• Types
• Accelerated aging (105 - 110ºF 100 RH) for
  2 - 5 days
• Cold test (used for warm-temp. crops like corn),
  imbibe and hold seed at 50ºF for 7 days then
  plant at 75ºF )
• Cool test (for veggies and flower seed),
  germinate at 64ºF
• Electrolyte leakage increases as seed
  deteriorate. Measure using conductivity meter

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Sources of seed

• Seed treatments
• Seed protectants
• Chemical treatments - powders. liquid, slurry
• Copper sulfate (1800s)
• Mercury compounds (1900s) - banned in 1980s
• Fungicides (1940-50 to present) Captan and Thiram
• Biocontrol
• Beneficial microbes (bacteria and fungi)

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Sources of seed

• Seed treatments
• Seed protectants
• Thermotherapy
• Hot water (120-135F) for 15-30 minutes
• Kills insects and some diseases
• Seed cannot be previously hydrated!
• Seed coating
• Pelletized (1000 heavier)
• Film-coated (1-5 heavier)

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Thiram treated seed
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Pelletized petunia seed
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Sources of seed

• Germination enhancement
• Primed seed (lettuce and pansy)
• Pregerminated - sow using fluid drilling
• Regerminated - seed will resprout after drying
  completely following germination (rare)

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Sources of seed

• Seed storage duration
• Recalcitrant or short-lived seeds
• Spring-ripening temperate trees (like some Acer,
  Populus, Salix, Ulmus)
• Nut trees (Aesculus, Carya, Corylus, Castanea,
  Fagus, Jugans, Quercus)
• Tropical plants
• Aquatic plants

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Sources of seed

• Orthodox seed
• Medium-lived seeds (2-15 years)
• Low RH and low temp.
• Long-lived seeds (15 - 100 years)
• Lotus seed that germinated was 100-430 years old !

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Sources of seed

• Storage factors
• Moisture content most important factor for
  longevity!
• 4-6 for storage
• 40-60 for germination
• Recalcitrant seeds are sensitive to low moisture
  storage and therefore require gt40 cool temps.
• Temperature
• Subfreezing to 32ºF low moisture (except for
  tropical and sub-tropical plants!)

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Sources of seed

• Cryopreservation
• Uses liquid nitrogen (-196C or -320F)
• Seed must be dry before freezing
• Containers
• Aluminum pouches
• Aluminum cans
• 3 mil polyethylene
• Aluminum-lined paper
• Desiccant silica gel with cobalt chloride as an
  indicator (blue dry, pink gt 45 RH)

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