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Seed Testing and Storage Recommendations for Tree and Shrub Seed
United States Department of Agriculture
Forest Service October 2018
American Chestnut Foundation - 35th Annual Meeting Huntsville, AL - October 27, 2018
by Victor VankusUSFS National Seed Laboratory
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Seed Testing and Storage of Tree and Shrub Seed
Factors Influencing Seed Quality Genetics
Environmental and Other Conditions from Flowering through Harvest
Insects and other Pests
Post Harvest ConditionsSeed Collection, Processing, Storage conditions
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Seed Testing and Storage of Tree and Shrub Seed
Seed TestingConducted to assess the condition of a seed lot at that
point in time.
Test results guide our actions for handling and managing seed collections.
– Do we collect these seeds?– Do we keep these seeds?– What are the physical components and number of seed?– What is the viability and moisture status?
Is the seed lot in the desired condition for storage?
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Seed Testing and Storage of Tree and Shrub Seed
Types of Seed Tests
PuritySeed CountViability
x-ray, germination, tetrazolium, excised embryoMoisture
moisture content, equilibrium relative humidity (ERH)
Association of Official Seed Analysts (AOSA)International Seed Testing Association (ISTA)
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Seed Testing and Storage of Tree and Shrub Seed
Purity TestPhysical purity – determination of the percent by
weight of pure seed in the lot.
Components identifiedPure seeds (specific definitions of pure seed units according to the “Rules for Testing Seeds” by the Association of Official Seed Analysts)
Inert mater (dirt, sticks, broken seed, ….)
Other seeds Crops, Weeds
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www.nps.gov/plants/sos/bendcollections
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Seed Testing and Storage of Tree and Shrub Seed
Purity TestStorage collection should contain pure seed and as little inert material as practical to obtain through cleaning.
Other seeds and inert material may contain water and can significantly increase the volume of the collection to be stored.
Purity test results can be used to manage seed harvest practices, initial seed processing, and to determine whether additional cleaning is required.
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Seed Testing and Storage of Tree and Shrub Seed
Seed Count
Determined on pure seed.
Number of seeds per pound.
Required to determine pure live seed (PLS) per pound.
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The Role of Seed Analysis in Genetic Conservation
Viability Testing – X-ray
Examine the condition of a seed lot quickly and accurately.
Non destructive.
May not be a good estimate of germination.
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Seed Testing and Storage of Tree and Shrub Seed
Viability Testing - TetrazoliumChemical test - tetrazolium salt reacts with enzymes inside the
seed to stain living tissue red.
Relatively quick vs. germination.
Dormant seedDetermine viable dormant seed at the end of a germination test - Independent of dormancy (usually).
Only alternative to quickly estimate viability for many species.
Requires training and experience to accurately estimate viability.
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Preparation for Staining
Expose the Tissue
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EvaluationStaining patternsTurgidityEssential structures
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Seed Testing and Storage of Tree and Shrub Seed
Viability Testing – Excised Embryo Test
Embryo removed from the seed and is free from the seed coat and nutritive tissue.
Relatively quick vs. germination
Analyze embryo characteristics and growth.
Closer to germination test - less subjective than tz.
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Seed Testing and Storage of Tree and Shrub Seed
Viability Testing – Germination
Precise conditions for temperature, light, media, pretreatments, reporting. Standardized rules for many species.
Determine the maximum number of seeds that will produce a normal seedling.
Repeatable results
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Seed Testing and Storage of Tree and Shrub Seed
Moisture Testing
Regulating seed moisture is the most important factor in preserving seed viability.
How much water is in the seed?
Are the seeds metabolically active? Respiring?
Is it safe to freeze the seed for storage?
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Moisture content thresholds and potential effects on stored seeds of most species
Percent Effects
>30 Germination begins
18 to 20 Overheating from respiration in storage
10 to 18 Seed fungi become active
>9 Insect activity
4 to 8 Best range for sealed storage
<4 Desiccation damage possible in some species
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Seed Testing and Storage of Tree and Shrub Seed
Equilibrium Relative Humidity (ERH)
Monitors Seed Moisture
How much water is in the seed?
Are the seeds metabolically active? Respiring?
Is it safe to freeze the seed for storage?
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Water Activity Meter
Probe
Meter
Sample holder
A water activity (Aw)meter used to measure ERH.
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Hygrometer measuring ERH of seeds in a covered box
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Equilibrium Relative Humidityvs. Moisture Content
05
101520253035404550
10 20 30 40 50 60 70 80 90 100erh
mc
variousspeciesFraser fir
longleafpine
green ash
jack pine
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Seed Testing and Storage of Tree and Shrub Seed
Key points of ERH
• Water Activity is another term that is used for ERH• Can be used on any seed lot regardless of
– Viability– Purity– Stage of extraction– Species
• No conversion charts needed• Traceable standards available for calibration• Non destructive• Fast – Results obtained in a few minutes• Very easy to use• Low cost equipment ($200 to $2500)
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Seed Testing and Storage of Tree and Shrub Seed
Seed TestingConducted to assess the condition of a seed lot at that
point in time.
Test results guide our actions for handling and managing seed collections.
– Do we collect these seeds?– Do we keep these seeds?– What are the physical components and number of seed?– What is the viability and moisture status?
Is the seed lot in the desired condition for storage?
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Seed Testing and Storage of Tree and Shrub Seed
Factors Influencing Seed Quality Genetics
Environmental and Other Conditions from Flowering through Harvest
Insects and other Pests
Post Harvest ConditionsSeed Collection, Processing, Storage conditions
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Seed Testing and Storage of Tree and Shrub Seed
Seed StorageFactors Affecting Viability and Longevity of Seed in Storage
– Seed maturity– Genetics– Year – annual effects– Physical damage – processing– Physiological deterioration – handling, transport, mc– Fungi and insects– Initial viability
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Seed Testing and Storage of Tree and Shrub Seed
Seed StorageIs the seed lot in the desired condition for storage?
– Moisture content
Are the storage conditions appropriate?
– Temperature– Humidity– Air exchange– Packaging/Container
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Moist seed
Dry air (Relative humidity is below 30%)
Water leaves the seed and goes into the dry air.
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Dry seed
Humid air (relative humidity is above 30%)
Water moves from the air into the dry seed.
To keep seeds dry they must be sealed in a moisture proof container.
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Moist Seed
Humid air (70%)
Water moves both ways or not at all.
The condition of a high equilibrium relative humidity. At equilibrium this seed will measure an ERH of 70%.
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Dry Seed
Dry air (25% relative humidity)
Water moves both ways or not at all.
The condition of a low equilibrium relative humidity. At equilibrium this seed will measure an ERH of 25%.
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Seed Testing and Storage of Tree and Shrub Seed
Scheduling Seed Tests
Throughout collection and processing as needed.
After processing and prior to storage.
During storage - Monitor moisture and viability over time
Prior to sowing or grow out – check viability
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USDA Forest ServiceNational Seed Laboratorywww.fsnsl.fs.fed.us
United States Department of Agriculture
Forest Service