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Seeds, Germination, Emergence

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  1. Seeds, Germination, Emergence Seeds contain embryonic plants. Embryo is alive Dormant condition Genetically modified. Dependent upon people. Understanding of seed anatomy and germination critical to maximize crop production. Healthy plants – large seeds. Management decisions. Cultivar Planting Rate Planting Date Planting Depth Size from 22 lbs (coconut) to 5M/lb (tobacco)

  2. Seed Size, Shape and Color Can affect handling during storage and seeding. Shape: • Form • Affects planter. • Rounds, flats – corn • Awns – wheat, barley, rye Size: • Does not determine plant size. • Can produce seedling effect. • Affects planter. • Affects planting depth. Color: • Does not affect planting or production. • Marketing – kernel red streak

  3. Fruit vs Seed Fruit: Mature ovary with 1 or more ovules Seed: Mature ovule containing embryo Agriculture Seed Definition: Unit planted and/or sold Kernels per acre – 80,000k corn 28,000 ppa Pounds per acre – 87#/A wheat = 1.3M ppa 120,000 – 150,000 ppa soybeans Legume – pod splits in half

  4. Major Tissue Components of Seeds Seed Coat: Dehiscent:removable Indehiscent: not removable Embryo: Immature plant Cotyledons: Embryonic axis: Cotyledonary node: where cotyledons and embryonic axis attached Embryonic Axis: Radicle: embryonic root Epicotyl: stem above cotyledonary node Hypocotyl: stem below cotyledonary node Food Source:cotyledons or endosperm Plumule: 1st embryonic bud, stem portion above cotyledons Fig. 2-37

  5. Dicot (legume) Seed Morphology Two cotyledons – stored food in seed Structures: Raphe:seed ridges opposite of embryo formed by stalk of ovule Hilum: scar point of attachment of ovule to ovary, nutrient transfer Embryo: immature plant Testa: seed coat, protective, dehiscent Hypocotyl: stem below cotyledonary node Radicle: embryonic root Epicotyl: stem above cotyledonary node Cotyledons: seed food reserve, protein, oil Acquuah Fig. 2-36

  6. Monocot Caryopsis (not true seed) Morphology Monocot – one cotyledon Pericarp: outer covering fused to ovary wall, dehiscent Aluerone Layer: lines inside pericarp and outer layers of endosperm, enzymes that breakdown endosperm Endosperm: carbohydrate food source Scutellum (cotyledon): enzymes digest endosperm Coleoptile: protective sheath for emerging leaf Epicotyl (plumule): stem above cotyledonary node Apical Meristem: growing point of embryo Scutellar Node: attachment of cotyledon to embryo Radicle: embryonic root Coleorhiza: protective sheath around radicle Tip (pedicle): attachment point kernel to flower stock Black Layer: dead cell layer, physiological maturity Acquuah, Figure 2-37 Page 93

  7. Forage/Cereal (Caryopsis) Grain Identification Based on Spikelet: Glumes: attached to rachis on sides of caryopsis Lemma: outer layer adhering to caryopsis Palea: outer layer adhering to caryopsis Barley Spike

  8. Seed Germination Respiration and metabolism continue throughout seed dormancy Germination: • embryo resumes normal growth and metabolism • some require a dormant period • environmental requirements: • Oxygen: metabolism • Adequate Temperature: enzymes • Adequate Moisture: hydration • Light: stimuli

  9. Seed Germination and Emergence Germination: Emergence and development from embryo. Structures to produce normal plant. Stages: I. Activation: water uptake (imbibed 10 – 30 minutes) 5 – 10 hour wetting stage no metabolic energy required protein synthesis and enzymes activated. respiration rate increases II. Digestion and Translocation: enzymes loosen seed coat food reserves translocated  radicle and plumule. mitochondria active (ATP) protein synthesis III. Cell Division and Elongation: radicle emerges by cell enlargement and division (1-2 days) followed by plumule (shoot) Corn Soybean

  10. Epigeal Seed Emergence (Dicot) Seedling Emergence: Appearance of embryo above soil. Epigeal: 90% of dicots (soybeans) • Cotyledons emerge preceded by hypocotyl arch (soybean) • Light cause hypocotyl to stop growing. • Cotyledons become green  shrivel and fall off Acquuah Fig. 16-2, Page 475

  11. Hypogeal Seed Emergence See Fig. 16-3 Corn All monocots (corn), 10% dicots (pea) • Coleorhiza emerges followed by radicle. • Coleoptile emerges above soil, inhibited by light • followed by true leaves. Peas

  12. Grass Family (Poaceae) vs Legume (Fabaceae) Family Grass FamilyLegume family Cotyledon 1 2 Food Supply endosperm cotyledons Food Type starch protein & oil Cotyledon Function food absorption food storage Coleoptile present absent Coleorhiza present absent Hypocotyl inactive active Epicotyl Mesocotyl present

  13. Seed Certification Process Breeders Seed Developed and Maintained by Breeder Foundation Seed Increased by company Registered Seed Increased by company Certified Seed Production Fields Plant Variety Protection Act 1970 20 PVP and 4 Patents

  14. Factors Affecting Viability of Stored Seed Seed Moisture + Temperature < 100 Seed Moisture: Most important 8-10% generally, 4-6% long term Insects, mold Temperature: 35oF – 25OF best Humidity: 20% - 40% Seed Age: Carryover retested 20 – 30 years for cereals and legumes 5 - 6 years for grass seed

  15. Seeds, Germination and Emergence Seed Testing: Determine capacity of seed to establish seedling stand. Federal Seed Act of 1939 Cultivar name % germination % pure seed % weed seed Seed Quality Affected by: Physical Genetic Maturity Nutrition and Moisture Environmental Abiotic – temperature and humidity Biotic – disease and insects

  16. Commercial Seed Tag Kind and Variety: corn and hybrid name Lot Identification: production field Pure Seed: % Other Crop Seed: % by weight Weed Seed: % by weight Inert Material: % by weight ProhibitedNoxious Weeds:field bindweed, Canada thistle Restricted Noxious Weeds:allowable limit, quackgrass Germination:% normalvigor Date of Test:year and month Origin:where produced Name and Address: company

  17. Seed Purity Test Percentage of crop seed. • Seed of other crops • Weed seed Noxious – difficult to control Prohibited– disqualify seed from sale Restricted– limited amounts allowable • Inert matter

  18. Seed Viability Testing Germination seed under favorable conditions. • Warm Test Rolled-towel test: 8 reps 50 seeds each rep seeds placed on paper rolled 90% humidity, 25oC (77oF) 7 days After specified time seed lot rated: Normal Hard Abnormal Dormant Dead or decaying

  19. Seed Viability Testing 2.Tetrazolium Test: • Soak seed over night • Enzymes become active • Cut seed in half • Soak in tetrazolium • Tetrazolium turns red when reduced by H+ • Staining Pattern • Viable seed turn red • Will germinate if radicle margins red • Dead seeds remain colorless

  20. Seed Vigor Test Strength of germination. • Cold Test Soil layer over paper towels 10oC (50oF) for 7 days  25oC (77oF) for 3 days Seed lot rated • Accelerated Aging: 45oC (113oF) & 100% humidity for 3-4 days Germinated under favorable conditions • Mechanical Damage: Soak in 0.1% bleach 15 minutes Cracked seed will imbibe, testa separate

  21. Internal Factors Affecting Germination Physiological Maturity: Dry matter no longer added. • Soybeans –enzymes produced as seed matures and dries • Problem: immature seed • lacks seed coat protection • special storage • difficult to plant Seed Size: • Large seed produce vigorousseedlings

  22. External Factors Affecting Germination Water: Activates enzymes to translocation food Temperature: Cool-temp seeds - <50oF, onion, radish, lettuce Warm-temp seeds - >50oF corn, tomato >60oF soybeans, sorghum Air: O2 required for respiration CO2 (0.03%) inhibits germination Light: Phytochrome: light sensitive pigment affected by photoperiod Lettuce - red stimulates germination, far red inhibits, darkness prevents germination Biotic: Disease and insects controlled by treatment

  23. Seed Dormancy Quiescent Seed:germination in favorable conditions Dormant Seed:no germination in favorable conditions 1. Physical: non-embryo Seed Coat: impermeable = hard seed (alfalfa, red clover) Scarification – loosen seed coat (abrasives, hot water, acid, microwaves) Mechanical: prevents embryo expanding (stone fruits) Chemical: accumulation of chemicals (flax) 2. Physiological: most common, in embryo Metabolic inhibitor 1-6 month overwintering – break down chemicals Stratification - chilling in sand Under-developed embryo (carrot), age of plant, moisture content (drought) Non-dormant  dormant (high temperature on winter barley)

  24. Obtaining Good Stands in Corn Most complaint calls occur in the spring. Seed: Genetics, quality, maturity, seed size Soil Moisture: Don’t pack in mud & don’t store in dry soil. Soil Temperature: 50oF at 3” depth Planting Date: Done by May 10 Soil Type: Determines depth, rate, genetics Planting Depth: Soil moisture & temperature – 1.5” Seeding Rate: Shoot for finished stand over 28,000 ppa for 200+ bu/A Row Width: 15” vs 30”, no wider, uniform within row Spread your risk = genetics, maturity, disease and insect resistance, fertility