•   Major methods of enhancing seed:
  • Seed hydration
  • Biological seed treatments
  • Seed coating

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• Seed Hydration
  • A process whereby seeds are hydrated using various protocols and then redried to permit routine handling
  • Anticipated results:
    1. Increased germination rate
    2. More uniform emergence
    3. Germination under broader range of environments
    4. Improved seedling vigor and growth
  • Principle: Hydrate seed to initiate early germination events, but not sufficient enough to permit protrusion

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  • General Approaches
    1. Prehydration
    2. Priming
    3. Solid Matrix Priming

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  • Prehydration
    • Controlled soaking in water
    • Fluid drilling (presoaking in gel @ 20⁰C
    • Hydroxyethyl cellulose
    • Magnesium silicate
    • Polyacrylamide
    • May also include:
      1. Carbon
      2. Nutrients
      3. Pesticides

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  • Priming (osmoconditioning)
    • Soaking seed in aerated low water potential osmotica
    • Use salts to supply N & other nutrients
    • PEG (polyethylene glycol) most common
    • Disadvantage is occasional toxicity & O₂ soluability
    • Most successful on small-seeded crops

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  • Solid Matrix Priming (matriconditioning)
    • Involves solid carriers
    • Ideal characteristics
      1. Low matrix potential
      2. Negligible water soluability
      3. High water-holding capacity
      4. High surface area
      5. Non-toxic to seed
      6. Readily adheres to seed

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  • Natural Carriers
    • Vermiculite
    • Peat moss
    • Sand
    • Bituminous coal
    • Commercial products
      1. Celite
      2. Micro-Cel
      3. Zonolite
      4. Leonardite shale

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  • Physiological mechanisms involved:
    • Reduces imbibitional damage
    • Less secondary dormancy
    • May provide for repair of deteriorated seed parts

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  • Factors that affect performance:
    • Ambient conditions
    • Types of osmotica
    • Oxygen availability
    • Duration of treatment
    • Control of microbial contamination
    • Drying

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• Biological Seed Treatments
  • Use of fungi or bacteria to control soil and seed pathogens
  • Advantages:
    • Fewer safety concerns for humans and environment
    • May protect plant until maturity
    • Have narrow range of specificity
    • Markedly enhance plant performance
  • Disadvantages:
    • Often influenced by the micro-environment
    • Efficacy dependent upon the population involved
    • Handling & application may require sterile conditions

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• Seed Coatings
  • Is one of the most successful areas of seed enhancements
  • Uses:
    1. Enhance seed placement and performance by changing shape or size
    2. Place chemicals on the seed coat to improve germination
  • Seed Pelleting
    • Is applied to improve plantability and performance
      1. Non-round seeds
      2. Small and/or light seeds
    • Materials include:
      1. Amalgam of fillers (clay, limestone, calcium carbonate, vermiculite)
      2. Cementing additives (gum arabic, gelatin, methycelluose)
      3. Beneficial chemicals may be added:
         • Plant hormones
         • Micronutrients
         • Fungicides
  • Seed Coating
    • A substance is applied to the seed, but the shape is not obscured
    • Examples:
      1. Fungicides
      2. Insecticides
      3. Safeners
      4. Micronutrients
    • Desirable traits of a seed coating:
      1. Provide excellent plantability
      2. Contain no "dust-off" of additives
      3. Provide for excellent germination under all environments
    • Advantages:
      1. Can use wide range of application equipment
      2. Requires less chemical than broadcast methods
      3. Material is intact with the seed

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  • Synthetic Seeds
    • Advantages:
      1. Somatic embryos may be used to produce uniform plant population
      2. May circumvent self-incompatabiltiy and long breeding cycles
      3. Allow utilization of hybrid crosses in some crops
         • Cotton
         • Soybean
    • Principle of somatic embryos:
      • Are produced asexually from vegetative tissue
      • Are clones that possess identical characteristics
    • Challenges:
      • Multiple somatic embryos are common in different stages of development
        • May lead to precocious germination
        • Harvest timing is difficult
      • Quiescence phase is frequently missing
    • Encapsulation
      • Used as a means for inducing dormancy
      • Types:
        1. Hydrated
           • Calcium alginate is applied prior to planting
        2. Dry
           • Hardened coating allows for storing and handling

References:

Principles of Seed Science and Technology. 3rd Ed. L.O. Copeland and M.B. McDonald. Chapman and Hill, New York, 1995

Seeds Handbook, B.B. Desai, P.M. Kotecha and D.K. Salunkhe. Marcel Dekker, Inc., New York, 1997.