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Chapter 6

Chapter 6. Sources of seed. 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

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Chapter 6

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  1. Chapter 6 Sources of seed

  2. 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

  3. Seed Exchange http://www.seedsavers.org/

  4. http://www.southernexposure.com/

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

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

  7. Sources of seed • Harvesting and processing • Types of fruits • Fleshy fruits - fruits & vegetables crops (berries, pomes, drupes)

  8. 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 @ 70°F (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)

  9. 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.)

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

  11. Sources of seed • Germination tests • Use 400+ seeds • Divide into lots of 100 • If germination of lots differ by >10%, retest 100 100 100 100

  12. 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

  13. 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 - 74°F

  14. 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

  15. Sources of seed • X-ray analysis • Does not test for viability • Checks for filled seeds • Checks for insects • Seeds must be > 2 mm

  16. 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

  17. 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

  18. 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

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

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

  21. Thiram treated seed

  22. Pelletized petunia seed

  23. 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)

  24. 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

  25. 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 !

  26. 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 >40% & cool temps. • Temperature • Subfreezing to 32ºF + low moisture (except for tropical and sub-tropical plants!)

  27. Sources of seed • Cryopreservation • Uses liquid nitrogen (-196°C or -320°F) • 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 = > 45% RH)

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