1. Seed Dormancy of Trees and Shrubs by Jill Barbour Germination Specialist USDA Forest Service USDA Forest Service National Tree Seed Laboratory National Tree Seed Laboratory

2. Organic Seed Dormancy EndogenousEndogenous embryo characteristic prevents germination-epicotyl, hypocotyl, radicalembryo characteristic prevents germination-epicotyl, hypocotyl, radical Exogenous Exogenous characteristic of structures - seed coats, fruit walls, including endosperm or perisperm prevents germinationcharacteristic of structures - seed coats, fruit walls, including endosperm or perisperm prevents germination

3. Types of Seed Dormancy PhysiologicalPhysiological MorphologicalMorphological MorphophysiologicalMorphophysiological PhysicalPhysical Physical & physiologicalPhysical & physiological ChemicalChemical MechanicalMechanical

4. Physiological Dormancy NondeepNondeep IntermediateIntermediate DeepDeep

5. Causes of Physiological Dormancy Covering restricts oxygenCovering restricts oxygen Inhibitors in coveringsInhibitors in coverings Embryo cannot break through physical barriersEmbryo cannot break through physical barriers Endosperm restrict embryo growthEndosperm restrict embryo growth Interaction between embryo and coveringInteraction between embryo and covering Abies alba, Castanea sativa, Corylus avellana, Euonymus europaeus, Juglans nigra, Juglans regia, Juniperus, Prunus avium,Rhamnus frangula, Vaccinium myrtillusAbies alba, Castanea sativa, Corylus avellana, Euonymus europaeus, Juglans nigra, Juglans regia, Juniperus, Prunus avium,Rhamnus frangula, Vaccinium myrtillus Carpinus requires warm followed by cold stratificationCarpinus requires warm followed by cold stratification Elaeagnus umbellata- chemicals shortened prechilling & increase germinationElaeagnus umbellata- chemicals shortened prechilling & increase germination

6. Nondeep Physiological Dormancy Germinate over a narrow range of temperaturesGerminate over a narrow range of temperatures Excised embryos usually growExcised embryos usually grow Broken by short periods of prechillingBroken by short periods of prechilling Require germination temperature above 15°CRequire germination temperature above 15°C Broken by chemicals- potassium nitrate, thiourea, kinetin, ethylene, gibberellinsBroken by chemicals- potassium nitrate, thiourea, kinetin, ethylene, gibberellins Light required for germinationLight required for germination Arbutus unedo –can germinate in darkArbutus unedo –can germinate in dark Ulmus glabra- no prechillUlmus glabra- no prechill Vaccinium- long period of light required, GA reduces length of lightVaccinium- long period of light required, GA reduces length of light

7. Intermediate Physiological Dormancy Excised embryos will growExcised embryos will grow As much as 6 months prechilling neededAs much as 6 months prechilling needed Gibberellins, kinetin, thiourea can shorten prechilling requirementGibberellins, kinetin, thiourea can shorten prechilling requirement Acer negundo, Acer pseudoplatanus, Acer saccharum, Corylus avellana, Fraxinus americana, Fraxinus pennsylvanicaAcer 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, GA 3 increased germination of unchilled seeds at 15°C, 10 weeks prechill negate chemical effect (Seed Sci 2004, p21-33)Fagus sylvatica – ethylene accelerated and increased germination at 15°C, at 5°C chemicals no better than water soak on germination, GA 3 increased germination of unchilled seeds at 15°C, 10 weeks prechill negate chemical effect (Seed Sci 2004, p21-33)

8. Deep Physiological Dormancy Excised embryos do not grow or produce abnormal seedlings (Prunus will)Excised embryos do not grow or produce abnormal seedlings (Prunus will) Long prechill requirementLong prechill requirement Chemicals do not affect germination of intact seedsChemicals do not affect germination of intact seeds Sorbus aucuparis – secondary dormancy induced above 20°C, germinates best at 1-3°CSorbus aucuparis – secondary dormancy induced above 20°C, germinates best at 1-3°C Acer platanoides, Acer tartaricum, Malus domestica,Acer platanoides, Acer tartaricum, Malus domestica, Prunus persica – 90 days prechillPrunus persica – 90 days prechill Prunus mahaleb – 100 days prechillPrunus mahaleb – 100 days prechill 3 to 5°C best germination temperature for Prunus mahaleb, Prunus padus3 to 5°C best germination temperature for Prunus mahaleb, Prunus padus

9. Morphological Dormancy Morphology of embryo not developedMorphology of embryo not developed Temperate families- Apiaceae, RanunculaceaeTemperate families- Apiaceae, Ranunculaceae Tropical families – Annonacease, Arecaceae, Degeneriaceae, Lactoridaceae, Monimiaceae, Myrsticaceae, WinteraceaeTropical families – Annonacease, Arecaceae, Degeneriaceae, Lactoridaceae, Monimiaceae, Myrsticaceae, Winteraceae

10. Morphophysiological Dormancy Underdeveloped embryosUnderdeveloped embryos Embryo growth and dormancy break requiredEmbryo growth and dormancy break required Embryo grows first then dormancy broken or both at same timeEmbryo grows first then dormancy broken or both at same time Vary warm, moist and cold stratification periodsVary warm, moist and cold stratification periods Viburnum- epicotyl dormancy, warm for radical then cold for epicotylViburnum- epicotyl dormancy, warm for radical then cold for epicotyl Fraxinus excelsior, Magnolia acuminata Fraxinus excelsior, Magnolia acuminata

11. Physical Dormancy Present in 15 angiosperm familiesPresent in 15 angiosperm families Large embryos with food reserve in embryo not endospermLarge embryos with food reserve in embryo not endosperm Hilum impermeable in Cercis siliquastrumHilum impermeable in Cercis siliquastrum Impermeable in seed coats- micropyle, hilum, chalazal area, impermeable palisade cellsImpermeable in seed coats- micropyle, hilum, chalazal area, impermeable palisade cells Embryo is not dormantEmbryo is not dormant Air drying during development intensifies hardnessAir drying during development intensifies hardness Cytisus scoparius – dry heat(65°C) for 2 minutes, or acid for 30 minutesCytisus scoparius – dry heat(65°C) for 2 minutes, or acid for 30 minutes Crataegus in warm climates only endocarp dormantCrataegus in warm climates only endocarp dormant Robinia pseudoacacia, Laburnum anagroidesRobinia pseudoacacia, Laburnum anagroides

12. Physical & Physiological Dormancy Embryo dormancy usually broken firstEmbryo dormancy usually broken first Germinate at low temperatures (5, 10, 15°C)Germinate at low temperatures (5, 10, 15°C) Prechilling breaks physiological dormancyPrechilling breaks physiological dormancy Hot water, acid, or mechanical scarification effective before prechillingHot water, acid, or mechanical scarification effective before prechilling Cercis siliquastrum – 16 weeks prechilling = 77% germination(Jordan source)(2004 Seed Sci p 255-260)Cercis siliquastrum – 16 weeks prechilling = 77% germination(Jordan source)(2004 Seed Sci p 255-260) Cersis canadensis, Cotinus coggygria, Cotinus obovatus, SambuscusCersis canadensis, Cotinus coggygria, Cotinus obovatus, Sambuscus Tilia- endosperm is inhibitor, excised embryos growTilia- endosperm is inhibitor, excised embryos grow Crataegus – 3 month periods of cold-warm-cold- warm-cold=55% germination, apomixis commonCrataegus – 3 month periods of cold-warm-cold- warm-cold=55% germination, apomixis common

13. Chemical Dormancy Inhibitors in embryo, endosperm, seed coatInhibitors in embryo, endosperm, seed coat Leaching or seed coat removalLeaching or seed coat removal Seed may have physiological dormancy too so need prechillingSeed may have physiological dormancy too so need prechilling Abscisic acid inhibits germination when applied exogenouslyAbscisic acid inhibits germination when applied exogenously Nickel (20 mg/liter) increased germination of Picea abiesNickel (20 mg/liter) increased germination of Picea abies

14. Mechanical Dormancy Stony endocarpsStony endocarps Embryos with deep physiological dormancy - require long prechillingEmbryos with deep physiological dormancy - require long prechilling Anacardiaceae, Cornaceae, Juglandaceae, Nyssaceae, OleaceaeAnacardiaceae, 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 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)Cornus mas- 18 week warm + 15-18 weeks cold stratification (Tylkowski 1991) Cornaceae not morphologically dormantCornaceae not morphologically dormant Elaeagnus angustifolia – snip both endsElaeagnus angustifolia – snip both ends Rosaceae - warm maturation temperature prior to collection reduced dormancyRosaceae - warm maturation temperature prior to collection reduced dormancy

15. Mattoral Germination Conditions Mean optimum germination temperature for trees about 21°C – during cool season when soil is moistMean optimum germination temperature for trees about 21°C – during cool season when soil is moist Mean optimum germination temperature for shrubs about 19°CMean optimum germination temperature for shrubs about 19°C Shrub seed germinate in light and darkShrub seed germinate in light and dark No shrub seed has morphological dormancy (underdeveloped embyros)No shrub seed has morphological dormancy (underdeveloped embyros)

16. Boreal & North Temperate Subalpine Pinus cembra- 90-270 days of prechillingPinus cembra- 90-270 days of prechilling No morphological, morphophysiological, physical dormancy in speciesNo morphological, morphophysiological, physical dormancy in species Pinus mugo, Picea abies – nondormantPinus mugo, Picea abies – nondormant

17. Jills Observations Small seeds usually from mesic areas, sometimes no endosperm(Ulmus), Sequoia, Sequoiadendron, Picea, PopulusSmall seeds usually from mesic areas, sometimes no endosperm(Ulmus), Sequoia, Sequoiadendron, Picea, Populus Large seeds from xeric areas – Pinus edulisLarge seeds from xeric areas – Pinus edulis Embryo size indicator of evolutionary development of Angiosperms, Magnolia precursor for Angiosperms with primitive embryoEmbryo 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 reproductive structuresAlpine seeds not very dormant, but may have undeveloped embryos, poor pollination = many empty seeds, short time for development of reproductive structures Dry summers, cold winters – many dormancy mechanisms to prevent germination, JuniperusDry summers, cold winters – many dormancy mechanisms to prevent germination, Juniperus