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– Seed exchanges, collection trips, seed

orchards, arboreta & botanic gardens

Seed ExchangeSeed Exchange

http://www.seedsavers.org/

http://www.southernexposure.com/

Sources of seed• Harvesting and processing– Types of fruits• Dry fruits - most Ag. crops (corn, wheat) do

NOT dehisce (“split-open”)

Sources of seed• Harvesting and processing– Types of fruits• Dry seeds - from fruits that dehisce

(pods, capsules, cones)

Sources of seed• Harvesting and processing– Types of fruits• Fleshy fruits - fruits & vegetables crops

(berries, pomes, drupes)

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)

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.)

http://www.seedtest.org/INDEX.cfm

Sources of seed• Sampling– Composite samples (collected from several

bags)

– Submitted sample (what is sent to be tested)

–Working sample (what is actually tested)

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

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

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

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

Sources of seed• X-ray analysis

– Does not test for viability

– Checks for filled seeds

– Checks for insects

– Seeds must be > 2 mm

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

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

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

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)

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)

Thiram treated seedThiram treated seed

Pelletized petunia seedPelletized petunia seed

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)

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

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 !

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!)

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)