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USDA Forest Service National Tree Seed Laboratory. Seed Dormancy of Trees and Shrubs. by Jill Barbour Germination Specialist. Organic Seed Dormancy. Endogenous embryo characteristic prevents germination-epicotyl, hypocotyl, radical Exogenous

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seed dormancy of trees and shrubs

USDA Forest Service

National Tree Seed Laboratory

Seed Dormancy of Trees and Shrubs

by Jill Barbour

Germination Specialist

organic seed dormancy
Organic Seed Dormancy
  • Endogenous
    • embryo characteristic prevents germination-epicotyl, hypocotyl, radical
  • Exogenous
    • characteristic of structures - seed coats, fruit walls, including endosperm or perisperm prevents germination
types of seed dormancy
Types of Seed Dormancy
  • Physiological
  • Morphological
  • Morphophysiological
  • Physical
  • Physical & physiological
  • Chemical
  • Mechanical
physiological dormancy
Physiological Dormancy
  • Nondeep
  • Intermediate
  • Deep
causes of physiological dormancy
Causes of Physiological Dormancy
  • Covering restricts oxygen
  • Inhibitors in coverings
  • Embryo cannot break through physical barriers
  • Endosperm restrict embryo growth
  • Interaction between embryo and covering
  • Abies alba, Castanea sativa, Corylus avellana, Euonymus europaeus, Juglans nigra, Juglans regia, Juniperus, Prunus avium,Rhamnus frangula, Vaccinium myrtillus
  • Carpinus requires warm followed by cold stratification
  • Elaeagnus umbellata- chemicals shortened prechilling & increase germination
nondeep physiological dormancy
Nondeep Physiological Dormancy
  • Germinate over a narrow range of temperatures
  • Excised embryos usually grow
  • Broken by short periods of prechilling
  • Require germination temperature above 15°C
  • Broken by chemicals- potassium nitrate, thiourea, kinetin, ethylene, gibberellins
  • Light required for germination
  • Arbutus unedo –can germinate in dark
  • Ulmus glabra- no prechill
  • Vaccinium- long period of light required, GA reduces length of light
intermediate physiological dormancy
Intermediate Physiological Dormancy
  • Excised embryos will grow
  • As much as 6 months prechilling needed
  • Gibberellins, kinetin, thiourea can shorten prechilling requirement
  • Acer negundo, Acer pseudoplatanus, Acer saccharum, Corylus avellana, Fraxinus americana, Fraxinus pennsylvanica
  • Fagus sylvatica – ethylene accelerated and increased germination at 15°C, at 5°C chemicals no better than water soak on germination, GA3 increased germination of unchilled seeds at 15°C, 10 weeks prechill negate chemical effect (Seed Sci 2004, p21-33)
deep physiological dormancy
Deep Physiological Dormancy
  • Excised embryos do not grow or produce abnormal seedlings (Prunus will)
  • Long prechill requirement
  • Chemicals do not affect germination of intact seeds
  • Sorbus aucuparis – secondary dormancy induced above 20°C, germinates best at 1-3°C
  • Acer platanoides, Acer tartaricum, Malus domestica,
  • Prunus persica – 90 days prechill
  • Prunus mahaleb – 100 days prechill
  • 3 to 5°C best germination temperature for Prunus mahaleb, Prunus padus
morphological dormancy
Morphological Dormancy
  • Morphology of embryo not developed
  • Temperate families- Apiaceae,Ranunculaceae
  • Tropical families – Annonacease, Arecaceae, Degeneriaceae, Lactoridaceae, Monimiaceae, Myrsticaceae, Winteraceae
morphophysiological dormancy
Morphophysiological Dormancy
  • Underdeveloped embryos
  • Embryo growth and dormancy break required
  • Embryo grows first then dormancy broken or both at same time
  • Vary warm, moist and cold stratification periods
  • Viburnum- epicotyl dormancy, warm for radical then cold for epicotyl
  • Fraxinus excelsior, Magnolia acuminata
physical dormancy
Physical Dormancy
  • Present in 15 angiosperm families
  • Large embryos with food reserve in embryo not endosperm
  • Hilum impermeable in Cercis siliquastrum
  • Impermeable in seed coats- micropyle, hilum, chalazal area, impermeable palisade cells
  • Embryo is not dormant
  • Air drying during development intensifies hardness
  • Cytisus scoparius – dry heat(65°C) for 2 minutes, or acid for 30 minutes
  • Crataegus in warm climates only endocarp dormant
  • Robinia pseudoacacia, Laburnum anagroides
physical physiological dormancy
Physical & Physiological Dormancy
  • Embryo dormancy usually broken first
  • Germinate at low temperatures (5, 10, 15°C)
  • Prechilling breaks physiological dormancy
  • Hot water, acid, or mechanical scarification effective before prechilling
  • Cercis siliquastrum – 16 weeks prechilling = 77% germination(Jordan source)(2004 Seed Sci p 255-260)
  • Cersis canadensis, Cotinus coggygria, Cotinus obovatus, Sambuscus
  • Tilia- endosperm is inhibitor, excised embryos grow
  • Crataegus – 3 month periods of cold-warm-cold-warm-cold=55% germination, apomixis common
chemical dormancy
Chemical Dormancy
  • Inhibitors in embryo, endosperm, seed coat
  • Leaching or seed coat removal
  • Seed may have physiological dormancy too so need prechilling
  • Abscisic acid inhibits germination when applied exogenously
  • Nickel (20 mg/liter) increased germination of Picea abies
mechanical dormancy
Mechanical Dormancy
  • Stony endocarps
  • Embryos with deep physiological dormancy -require long prechilling
  • Anacardiaceae, Cornaceae, Juglandaceae, Nyssaceae, Oleaceae
  • Cornus sanguinea – 94% germination at 12 weeks prechilling, 81% germination at 12 weeks warm + 12 weeks cold stratification(2004 Seed Sci p 1-4)
  • Cornus mas- 18 week warm + 15-18 weeks cold stratification (Tylkowski 1991)
  • Cornaceae not morphologically dormant
  • Elaeagnus angustifolia – snip both ends
  • Rosaceae - warm maturation temperature prior to collection reduced dormancy
mattoral germination conditions
Mattoral Germination Conditions
  • Mean optimum germination temperature for trees about 21°C – during cool season when soil is moist
  • Mean optimum germination temperature for shrubs about 19°C
  • Shrub seed germinate in light and dark
  • No shrub seed has morphological dormancy (underdeveloped embyros)
boreal north temperate subalpine
Boreal & North TemperateSubalpine
  • Pinus cembra- 90-270 days of prechilling
  • No morphological, morphophysiological, physical dormancy in species
  • Pinus mugo, Picea abies – nondormant
jill s observations
Jill’s Observations
  • Small seeds usually from mesic areas, sometimes no endosperm(Ulmus), Sequoia,Sequoiadendron,Picea, Populus
  • Large seeds from xeric areas – Pinus edulis
  • Embryo size indicator of evolutionary development of Angiosperms, Magnolia precursor for Angiosperms with primitive embryo
  • Alpine seeds not very dormant, but may have undeveloped embryos, poor pollination = many empty seeds, short time for development of reproductivestructures
  • Dry summers, cold winters – many dormancy mechanisms to prevent germination, Juniperus
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