Transcript Germination - University Of Georgia

Producing Plants From Seed
Paul A. Thomas
The University of Georgia
2012 Seed Germination Workshop
Teacher Training Conference
About Seeds
No Two Seeds Are Alike
Three Types Of Seed Sources
Fleshy Fruits:
Berries, Figs
Dry Fruits:
Grains, Grasses
Dry Seeds / Dehiscent Pods:
Cones/Pods
Heritage Heirloom
Varieties
Vegetables and flowers
that were grown and
passed on through many
generations by families.
Seedlings match parent
plants closely.
Terms To Know
Landraces – Populations of plants
maintained over hundreds of years by
farmers by holding over some of the
seed crop. This
allowed for local
specialization and
great differences
in genetic makeup
Terms To Know
Cross Pollination – Pollen from one plant
fertilizes the embryo sac of another plant
within the species.
Self Pollination – The pollen from a plant is
able to fertilize the embryo sac on the same
plant and produce a viable embryo.
Seed Collecting
Provenance : A seed’s origin, in
terms of climate and geographical
location. This can
Have profound effects on seed
germination and the plant’s
survival. Example: Hemlocks
grown from southern North
Carolina seed sources are more
heat tolerant than Hemlocks grown
from Pennsylvania seed sources.
Seed Collecting
Seeds collected from hybrid vegetables
and flowers s rarely look anything
like the parent plant due to the random
reassortment of genetic material, and
the random sources of pollen. Native
species tend to be more stable, but also
have variation between generations.
To get a clone, try vegetative propagation!
Seed Cleaning / Separation
Cleaning seed reduces
disease and weed seed
from growing along with
your selection
For many dry seed, simply
crush dried material and
blow gently, transferring
the seed from hand to hand.
Seed Deterioration
Seeds lose half their storage life for
every 1% increase in seed moisture
between 5 and 14%.
Seeds lose half their storage life for
every 5 degrees C increase in storage
o
o
temperature between 0 and 50 C.
Life Expectancy Of Selected Seeds
Sugar Maple
English Elm
Cocklebur
White Clover
Sensitive Plant
Indian Lotus
Artic Lupine
2 weeks
26 weeks
16 years
90 years
200 years
1,040 years
10,000 years
Terms To Know
Recalcitrant Seed – These seeds are able
to germinate without dessicating. These
seeds lose viability after drying and must
be planted quickly. Oak, Maple, Coffee
Orthodox Seed – The seeds dessicate
after reaching full development to allow
the seed to be quiescent or dormant until
conditions are right to germinate. Beans
Orthodox Seed
Short-Lived – Store dry and cold (Under 1 yr)
Vinca, Pansy, Begonia
Medium - Lived - Store dry and cold ( 2-5 years)
Marigold, Petunia, Coleus
Long - Lived – Store dry and cold ( 5-200 years)
Morning Glory, Zinnia, Hollyhock
SEED STORAGE
Recalcitrant Seed – Short-term Viability
Tropical – Store warm and moist (ASAP)
Coffee, Cocoa, Mango, Macadamia, Avocado, Tea
Subtropical – Store cool and moist (ASAP)
Maple, Oak, Elm, Poplar, Salix,
Seed Storage
o
Moist Storage @35 to 50 F
o
Dry Storage @ 35 to 50 F*
o
o
Cold Storage @ 0 F, –18 C *
o
Cryopreservation @ -196 C *
*** at 3 – 8% Moisture
Important Information
Directions
Planting Depth
Expiration Date
Source
More Information
Lot Number
Germination
Percentage
Scientific Name
Seed Coatings
•Fungicides/Rhyzobia
•Polycoating
•Pre-germinated
Enhanced
Seed
Park’s
Seed
Testing Viability - Simplified
The Cycle of Life
THE GERMINATION
PROCESS
How Germination Works
Water is usually the key
factor in starting the
germination process.
1. Imbibed water
stimulates
Gibberellin
synthesis.
2-3. Gibberellins
diffuse to the
aleurone layer and
stimulate the
synthesis of
enzymes.
4-5. Enzymes break
down the starch
and the sugars are
transported to the
developing embryo.
About Dormancy
Seed and Plant Dormancy
Dormancy is the condition
In which seeds will not
Germinate… even when
most of the environmental
conditions are permissive
for germination. There are
many types of dormancy!
Advantages of Seed Dormancy
• Favors seedling survival
• Creates a seed bank
• Seed dispersal (birds)
• Synchronizes germination with seasons
Relative Hormone Level
Triphasic Changes In Seed Hormone Balance
Overwintering of Seeds in the ground
100
75
ABA (Inhibits)
Cytokinin
Gibberellin
50
25
14oC
0
43
50
57
65
72
79
86
93 100
Days of Cold Stratification
Types of Dormancy in Seed
Quiescent – The seeds are able to Germinate upon
imbibition of water at permissive temperatures.
Primary Dormancy – Seeds cannot germinate
even if immediate conditions are right. This form of
dormancy delays germination until season, or other
macro-environmental issues are right for survival.
Secondary Dormancy – An additional level of
Protection to prevent germination. Can be induced under
very unfavorable conditions such as drought or cold, etc.
Types of Dormancy in Seed
Exogenous Dormancy - Imposed by
factors outside the embryo. Seed coat.
Endogenous Dormancy – Imposed by
factors within the embryo.
Underdeveloped embryo.
Exogenous Dormancy
• Physical – Impermeable seed coat : Scarification
• Mechanical – Seed covering restricts radical : Removal
• Chemical – Inhibitors in seed coat : Removal / Leaching
Endogenous Dormancy
Morphological - Underdeveloped embryo : Warm Stratification
Physiological
• Non-Deep – After Ripening : Dry storage
Photo-dormant : Exposure to red light.
• Intermediate – Embryo/coat separation : Cold Stratification
• Epicotyl – Epicotyl dormant : Warm - Cold Stratification
Types of Dormancy in Seed
Double Dormancy - Any combination
of endogenous and exogenous factors
Secondary Dormancy - Factors outside
the seed induce dormancy after the
seed was previously non-dormant. High
Soil Temperatures (Thermo-dormancy)
Double Dormancy
Morpho-physiological – Some combination of
underdeveloped embryo and physiological dormancy:
Cycles of warm and cold stratification.
Exo-Endodormancy – Combination of exogenous and
endogenous dormancy conditions
Sequential combinations of dormancy releasing treatments,
Eg. Scarification followed by cold stratification
Secondary Dormancy
• Thermo-dormancy - High temperatures induce dormancy
Growth regulators or Cold stratification
• Conditional – Change in ability to germinate is related to
time of year.
Chilling or Warm stratification
Photodormancy
Photodormancy : A type of dormancy
where the ability of the seed to germinate
is controlled by the wavelengths and
durations of light received by the embryo.
Lettuce, Butterflyweed, Tobacco
Types Of Photoperiodic Response
Whereas many plants are photoperiodic,
they do not all respond the same way.
Short Day Plants – Single Cycle……….Rice
Requires only one short day cycle to initiate the
photoperiodic response.
Long Day Plants – Single Cycle………….Dill
Requires only one long day cycle to initiate the
photoperiodic response.
Day Neutral Plants………………………………Cucumber
Flower the same time under all day-lengths, least
photoperiodic response.
Bright Sun
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Pfr
Dark
Reversion
Quiescence
(Slow)
Germination
Long hours of bright spring sun stimulates
formation of Pfr and germination begins!
Far Red Light
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Pfr
Dark
Reversion
Quiescence
(Slow)
Germination
Far-red light, such as is found under lots of vegetation,
prevents germination. Seeds wait for sun!
660 nm
Pr
Red Light
(Fast)
Far Red Light
Dark
Reversion
Quiescence
(Slow)
740 nm
Pfr
Darkness
Germination
Darkness maintains Pr and quiescence. Buried seed
won’t germinate until brought to the surface!
Techniques
Germination Environment
Moisture / Humidity
Temperature Range
Light Level and Quality
Aeration (Oxygen in Soil)
Soil pH and Nutrition
Air Movement
Technique
•
•
•
•
•
•
•
Berry Roll
Cracking
Scratching
Freezing
Moist Chilling
Hot Soaking
Irradiation
• You can use a
blender!
Irradiation
Germination Of Lettuce
Fleshy Berry Seed
Handling Tiny Seeds
Some seeds can be
smaller than the tip of
a pin. They can also
be very expensive. A
very careful approach
is often needed to be
efficient and successful
planting tiny seeds
Handling Tiny Seeds
Mix Seed with Sand
Preconditioning Seeds
(for more uniform germination)
Methods:
Mechanical scarification
Soaking In Water
Acid Scarification
Moist Chilling / Freezing
Double Dormancy
Mechanical Scarification
Acid Scarification
An alternative to
scraping the seed
coat is to use acid
to etch through
the coat. There
are many reference
books that advise
which acid and
how long to treat.
Hot Water Scarification
Water temperature should be over 110OF
Let soak for a few
hours. Stir often.
Do not re-heat
the water.
Plant ASAP.
Seed Soaking / Leaching
Seed soaking optimizes the amount of imbibed
seeds and evens out the stage of imbibition by
insuring 100% moisture availability
Soaking too long
can cause anoxia
and reduced
germination. 12-36
hours is a very
common soaking
period.
Thermo-hydro-Limitations
Time !
• Each species has a requirement for how many
hours the seed radical is exposed to a critical level
of moisture and/or soil temperature.
• Example: Cold, saturated soil inhibits corn
seedling radical growth after onset of germination.
• Local control: Use a heating pad and well drained
soils!
Moist Stratification
Cold or Warm
Sowing Success
•Proper seed bed
•Proper planting season
•Proper pre-treatment
•Proper seed handling
•Proper sowing depth
•Proper sowing rate
•Proper post-sowing care
Seedling Production Options
Community Pot
Seeding Box
Plug Tray
Fabric Matt
Hydroseeding
Direct Broadcast
Clean & Organized Environment
Fungicides
BanRot!
Follow The Label Directions!
Window-Box Propagation
Two clear halves of sweater/storage boxes taped
together with duct tape as a hinge make ideal
propagation boxes!
Place the box in a
sunny window, and
open it up for an hour
at night to replace air
and dry off leaves.
Works for almost all
tropical plants.
Germination Chambers
Preferred Night Temperature
Relative Growth Rate
100
75
15oC
30oC
Primula
Fern
Lantana
10oC
50
22oC
25
14oC
0
43
50
57
65
72
79
86
Degrees Fahrenheit
93 100
Root Zone Heating
Rooting medium temperature, given control, may be
applied to speed up growth. A good example is using
heating pads under planted seed flats to speed
up germination or rooting. The right temperature
can take a
week or month
off of rooting
schedule and
can take a few
days to a few weeks
off of germination.
Time is money.
Types Of Heating Technology
Hot Water Tubes
Electric Mats
Electric Heating Tapes
Mist Benches
We need to provide seedlings a film of water to
reduce evaporation, and the loss of water. Too
much water is as bad as too little water!
Light Levels Affect Seedlings!
As with mature plants, if cuttings are placed in too low
light conditions, they will get leggy and may abort leaves.
Even if they all live,
the final quality of
the adult plant is in
question. Which
plant will be thicker
and more branched?
Which would you buy?
Constantly Wet and/or Stagnant
Air Condition Affects Seedlings
The leaf surface of
seedlings benefits from
brief periods of surface
dryness, especially at
night. Air movement,
especially as new root
initials form, is essential
for root development.
Experiment One: The Seed Environment
A B C
Dark
Control
D E F
Vermiculite
Extract
Light
A=Asclepias, B=Catchfly, C=Black Eye, D=FoxGlove, E=Lettuce, F=Old Seed
Experiment Two: Germination Techniques
Freeze
PreSoak
Scratch
Scratch
A
B
C
D
sand
E
PreSoak
Crack
F
A=Blueberry, B=PoleBean, C=Lemon, D=Cherry, E=FoxGlove, F=Locust
Experiment Three: The Seed Environment
Lime
Fertilizer
D E F
Iron Sulfate
No Fertilizer
A B C
Control
A=Bean, B=Corn, C=Pumpkin, D=Cosmos, E=Burmuda, F=Marigold
Gardener
by Ann North
Some of the seeds of hope
Planted tentatively in the fall
Have not come up
They lie stillborn and unrealized
Somewhere in the spring soil
Decaying
The Strongest and best ones
Pushed up though the leaves
And layers of cold, hard resistance
Right into clear blue air
And stand there nakedly green
Breathing
It's always that way with growing things
Never knowing at the start
Which will make it and which will fail
But the thing to hold fast to
Never to lose faith in, is simply,
Sowing