Lab 4

• seed dormancy: a condition that exists in the seed as it is shed from the plant; seed will not germinate even under environmental conditions permissive for germination
• advantages of dormancy

  • allows storage, transport, and handling of seed
  • permits germination only when environmental conditions are favorable
  • create a "seed bank"
  • seed dispersal
• types of seed dormancy

  • primary dormancy
  • exogenous
  • endogenous
  • combinational
  • secondary dormancy
  • thermodormancy
  • conditional
• treatments to remove dormancy

  • scarification
  • for exogenous primary dormancy
  • species with hard seed coat
  • stratification
  • for endogenous primary dormancy
  • species that require periods of warm or chilling conditions
• scarification: process of physically or chemically altering seed coverings to improve germination in dormant seeds
• mechanical scarification

  • sandpaper
  • file or cutting with clippers
  • commercial scarifiers
• chemical scarification

  • concentrated sulfuric acid: 1 part seed 2 parts acid
• heat scarification

  • moist or dry sand above 35C
  • hot water at 77-100C
• stratification: a method of seed treatment in which seeds are subjected to periods of chilling or warm temperatures to alleviate dormancy conditions in the embryo; used to remove endogenous, physiological dormancy
• dry stratification

  • seed is subjected to cold temps of 32F or lower for a month or longer
  • keeping the seeds cold and dry helps increase germination rates by imitating a natural winter dormant period
• moist stratification

  • exposure to cold, damp conditions
  • seed is mixed with moistened material and stored cold for 10 days-3 months
• refrigerated stratification: small batches of seeds mixed with a moist substrate like vermiculite and placed in polyethylene bags
• Seed priming is a form of controlled seed hydration
• Seed priming can improve the germination properties of a seed lot, particularly germination rate and uniformity
• Radicle emergence is prevented by the water potential of the imbibitional medium
• After priming is complete, the seed is dried to nearly its original water content
• osmotic priming: imbibing seeds in osmotic solution with low water potential
• matrix priming: use of solid carriers with appropriate matric potential
• drum priming: hydrate seeds with water in a tumbling drum
• To achieve germination, 6 environmental conditions must be met:

  • Water must be available
  • Temperature must be in the acceptable range
  • Oxygen must be available
  • Light must be included/excluded
  • Pest/pathogen free seed
  • Salts must be kept low
• Dormancy is exhibited when seed will not germinate even under the proper conditions
• Exogenous primary dormancy can be physical (seed coat dormancy) or chemical (fruit or seed coat hormones are preventing seed from germinating)
• Exogenous primary dormancy can be overcome by cleaning seed properly and scarification
• Endogenous dormancy may be overcome by the exclusion/inclusion of light, gibberellic acid, or stratification