Lab 3

• 3 major root functions:

  • anchor plant in soil
  • absorb water & dissolved salts from soil
  • conduct water & salts to hypocotyl, cotyledons, and epicotyl
• hypocotyl (dicots and gymnosperms): portion of seedling axis between the root and the cotyledons; transition structure to epicotyl
• cotyledons (dicots and gymnosperms): storage structures of the embryo
• epicotyl: includes all seedling structures above the cotyledons
• terminal bud: at tip of epicotyl, the apical meristem
• hypocotyl (monocots): usually not discernable
• mesocotyl (monocots): between scutellum and base of coleoptile
• cotyledon (monocots): absorbs nutrients from the endosperm and transfers them to growing seedline
• coleoptile: present only in Poaceae; protective sheath enclosing terminal bud and developing leaves
• plumule: first leaf
• normal seedlings: seedlings with no defects or only slight defects will not impair the continued development of seedling/plant when grown in soil under favorable conditions
• abnormal seedlings: have defects which will prevent development into mature plants when grown in soil under favorable conditions
• environmental factors:

  • water
  • temperature
  • oxygen
  • light
  • pest/pathogen
  • salts
• light must be included/excluded
• generally, exclude light from large, heavy seed and allow light to shine upon small, lighter seed
• functions of a medium:

  • provide anchorage and support
  • provide an appropriate air-moisture balance for metabolic processes
  • should be stable and resistant to shrinkage or decomposition during production
  • adequate amount of air
  • high water holding capacity, allow excess water to drain freely
• Why not soil?

  heavy in weight, difficult to handle and transport, pathogens, efficiency
• important characteristics of medium:

  • must be sufficiently firm and dense
  • decomposed and stable
  • easy to wet and retain enough moisture to reduce frequent watering
  • sufficiently porous
  • free from pests
  • low salinity levels
  • high cation exchange capacity
  • consistent quality
  • should be readily available and economical
• root medium properties:

  • porosity
  • water holding capacity
  • nutrient holding capacity
  • bulk density
• sand:

  • use has declined, replaced by perlite
  • trucking costs
  • medium grade
  • little to no nutrients
  • mostly used with peat or perlite
• perlite:

  • lighter in weight, white in color, irregularly shaped particle
  • cannot hold water or nutrients
  • primary use: increase pore space
  • sterile, does not decay, drains freely
  • mined from crushed aluminum silicate volcanic rock
• vermiculite:

  • mined from mica-like ore
  • sterile and light
  • behaves like organic material - high nutrient and water holding capacity
  • contains high amounts of Ca, Mg, and K
  • good seed starter
• polysterene:

  • flakes and beads
  • light weight
  • difficult to mix
  • not very common
• rock wool:

  • inert, sterile
  • very high pore space volume of 98%
  • does not hold water or nutrients; drains freely
  • high durability
• synthetic foams:

  • plastic materials
  • high water holding capacity
  • friable, easily broken down
• sphagnum peat moss:

  • found in swampy areas
  • partially decomposed residue or mosses
  • preferred for propagation
  • high water holding capacity, decompose slowly, and have fungistatic properties
• wood by-products:

  • by-product of lumber industry
  • relatively light weight, low in salts, disease suppressing properties
  • pH varies
  • good substitute for peat
• coir:

  • waste remaining after coconut husks are processed for coir fiber
  • very open structure
  • slow to decompose
  • high water holding capacity
• compost and organic waste:

  • inconsistent quality
  • potential phytotoxicity, inconsistent pH
  • heavy
  • better porosity
• traditional "mix your own" media: 1:2:2 of sand, perlite, and peat
• Viability tests measures the number of seeds that are alive
• Germination test determines number of seeds that could germinate under favorable conditions
• Federal Seed Act regulates interstate shipment of seeds and requires proper labeling
• Blue blotter test is a type of germination test
• Tetrazolium can diffuse from one cell to another
• In TTC test, tetrazolium reacts with H to produce formazan
• Since watermelon is native to North Africa, it germinates at 90 degrees
• Small, light seeds need more light
• organic components of growing media:

  • compost
  • bark
  • peat moss
  • coir