Seed germination and seedling establishment

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Seed germination and seedling establishment

• Objectives of todays lecture
• Learn about horticultural practices that are used
  to promote seed germination and seedling growth
• Prenatal and postpartum care of plants

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Seed germination and seedling establishment

• 2 major uses of seeds in agriculture
• Plant part that is harvested for food, either
  directly or after processing
• Used for propagating plants
• a 23 billion market for seeds worldwide

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Why are seeds used for plant propagation?

• Advantages
• relatively inexpensive
• many seeds produced from a single plant
• convenient for storage
• naturally dormant in many cases
• long shelf life
• disease free propagation
• few pathogens carried by seeds

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Why are seeds used for plant propagation?

• Disadvantages
• Genetic segregation of traits - plants grown from
  seed may not be genetically identical to the
  parent plant examples include
• Seed produced from plants that are
  self-incompatible, e.g. apples
• Seed produced from F1 hybrids, e.g. onions, sweet
  corn

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Why are seeds used for plant propagation?

• Disadvantages
• Time to maturity
• Apple trees grown from seed may grow for 10 years
  before bearing fruit
• Potatoes grown from seed take 2 years to produce
  tubers

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Important criteria for seeds used in propagation

• Viability and vigor
• percent seed germination
• rate of germination
• rate of seedling growth

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Important criteria for seeds used in propagation

• For most horticultural crops viability and vigor
  are maintained when seed are stored at
• low temperatures
• low humidity
• Note that these are the opposite of the
  conditions that promote germination

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Long term storage of seeds

• Seeds of many species are kept under
  refrigeration for long term storage
• National Seed Storage Lab in Colorado
• repository for many species
• important for preservation of germplasm, a gene
  bank
• stored in liquid nitrogen
• seed are regrown every few years

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Seed quality

• Seed quality is important in commercial sales
• Federal and state regulations
• Indiana requires all seed to be tested (by the
  State Chemists Office) and labeled
• percent pure seed
• percent weed seed
• percent germination
• date of testing

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Conditions for seed germination

• Successful seed germination requires
• Viable, vigorous seed
• Adequate moisture
• Supply of oxygen
• Appropriate temperature
• Protection from pathogens and pests

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Seed dormancy

• Some seed will NOT germinate under standard
  conditions seed are dormant
• require specific treatments (temperature,
  abrasion, light) to break seed dormancy and
  before seed will germinate

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Breaking seed dormancy

• Stratification
• Scarification

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Methods of seeding

• Direct seeding
• Seeds are planted where the plants will grow to
  maturity or harvest
• Convenient to use
• Adaptable to mechanization
• Not well suited for very small seed
• Obtaining a good stand of plants requires soil
  preparation

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Methods of seeding

• Indirect seeding
• Two stage process with seeds germinated in a
  nursery before being transplanted to field
• Ensures good stand establishment
• Crop matures earlier
• Increased costs
• More difficult to mechanize
• Higher level of crop management

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Conditions for seed germination

• Successful seed germination requires
• Viable, vigorous seed
• Adequate moisture
• Supply of oxygen
• Appropriate temperature
• Protection from pathogens and pests

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Moisture is required for seed germination

• Seed survive at very low moisture
• Germination starts with imbibition,uptake of
  water into the seed
• Once seed are imbibed and development is
  initiated, the seedling is very sensitive to
  dehydration

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Moisture for germination

• Maintaining an adequate supply of water is
  essential for good germination
• In greenhouse (indirect seeding)
• thorough watering after seeding
• monitoring of soil moisture and regular watering
  or misting
• using plastic wrap to retain water
• Beware! Many pathogens thrive under high humidity
  conditions

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Moisture for germination

• Direct seeding
• preparation of seed bed
• good contact between soil particles and seeds
  facilitates uptake of water into seed
• planting at appropriate depth
• deep enough so the soil doesnt dry out
• shallow enough that the seed will emerge before
  its reserves are exhausted

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Germination requires oxygen

• Oxygen is readily available if seed is planted in
  a well drained, porous medium - soil or
  greenhouse mix
• Oxygen deprivation results from waterlogging,
  flooding or other soil drainage problems

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Temperature

• Requirement varies between species
• Temperature can be adjusted in greenhouse
• use of bottom heat
• In the field, planting depends on environmental
  conditions and weather, not necessarily the
  calendar

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Protection from pathogens

• Developing seedlings are a rich source of food
  for microbes
• Seedlings are relatively unprotected
• cuticle and other defenses are not fully
  developed in young seedlings
• Many fungal pathogens cause damping off of
  seedlings
• Phytophthora, Pythium, Rhizoctonia

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Protection from pathogens

• Preventive measures include
• soil pasteurization (180F, 30 min)
• using purchased sterilized soil mix
• clean containers
• controlling moisture
• using clean seed
• use of fungicides, seed treatments

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Seed coatings

• Seeds can be coated with a variety of compounds
  to enhance germination and seedling growth
• Fertilizer - to stimulate growth
• Insecticide - to prevent insect damage
• Fungicide - to inhibit growth of fungal pathogens

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Specialized seeding methods

• Hydroseeding
• Spray application of primed seed in a mix
  containing mulch and fertilizer

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Other seeding methods

• Liquid drilling
• Seeds are germinated under controlled conditions,
  until the radicle emerges
• Germinated seeds are mixed into a gel that
  contains fertilizer
• Mixture is sown in prepared field
• Pre-germinated seed promotes rapid growth of
  seedling

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Conclusions

• Seeds are living organisms, handle with care
• Successful establishment of seedlings requires a
  rapid transition from dry seed to autotrophic
  plant
• A variety of horticultural practices are used to
  promote seedling establishment