Chapter 6 Sources of seed Sources of seed

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 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. )

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

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: C 19 H 15 CIN 4 – 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 seed

Pelletized 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)