seed collection, processing and handling
TRANSCRIPT
Seed Collection, Processing and Handling
Objectives:
• Know the properties of ‘high quality’ seed.
• Understand basic seed biology and the reproductive
cycles for different BC conifers.
• Be familiar with biotic factors which affect the size and
periodicity of seed crops.
• Know the different methods of cone collection.
• Be able to describe the steps in conifer seed processing
and storage.
High quality seeds are: sound, store well, and have a
high capability to produce healthy seedlings that are
well adapted to the reforestation site and meet product
objectives.
Use of seed orchard seed is increasing yearly, but wild seed
collections still account for the majority of seed used in BC.
60%
90%
80%
80%
10%
Natural seed production varies from year to year - why?
11 crops
5 crops
35 years
Conifers are monoecious, having male and female flowers on same tree.
There are 4 key phases in the reproductive cycle:
Initiation
Differentiation
PollinationMaturation
There is an extended period between flower initiation and seed maturity.
The length of the reproductive cycle varies between species, from 16
months (‘2 year cycle’) to 30 months (‘3 year cycle’).
Year 1 Year 3Year 2
Large seed crops require different conditions during each developmental
phase. Heavy crops result from a series of optimal weather conditions at
each stage.
Initiation Differentiation Pollination Maturation
Date: spring, year 1 summer, year 1 spring, year 2
Factors: lots of
photosynthate
reserves and
shoot apices
warmth, high light,
good nutrition,
moisture stress
abundant,
well
distributed
pollen
good nutrition,
adequate
moisture,
warmth
Weather: cool, cloudy,
moist
warm, dry, sunny dry warm and
windy, no late
frosts
warm sunny,
periodic
rainfall
Cone crops vary from tree to tree within stands.
What factors does this depend on?
Quantities of cone and seed vary by species
and with position in crown:
Species Period-
icity
(years)
Location
of cones
in crown
Cones
/hl
Viable
seeds
/hl
Seeds
/
Cone
Clean
Seeds/
gram
Container
seedlings
/hl
Seed/
Seedling
Ratio
amabilis fir 2-3 Top 1/4 700 30000 43 33 18000 1.67
subalpine
fir
2-4 Top 1/4 850 40000 47 106 32000 1.25
interior
spruce
6 Top 1/3 10000 350000 35 512 73000 4.79
lodgepole
pine
2-4 All 8300 70000
interior
8 372 21000
interior
3.33
Douglas-fir
coast
interior
2-10
2-10
Top ½
Top ½
2800
2800
40000
70000
14
25
110
108
9000
14000
4.44
5.00
redcedar 2-4 All 110000 900000 8 882 260000 3.46
western
hemlock
3-4 All 83000 367000 4 528 98000 3.75
For wild seed collections, the objective is to collect during
medium or heavy seed years – why?
Sx Sx
Knowing the biology of seed production and the factors which
contribute to heavy, high quality seed crops informs seed
orchard management.
With these factors in mind, where should seed orchards be
located in terms of climate and proximity to natural stands?
• Sites should promote the growth of trees, but allow for drought stress
when desirable.
• Trees should be well spaced.
• Flowering can be induced through girdling, application of hormones
(gibberelic acids) and nitrogen fertilization; or delayed using sprinklers to
lower temperatures.
• All genotypes should produce pollen and seed cones at the same time –
so pick good producers as parents.
• Pollen contamination from surrounding stands introduces maladaptation
to source climate and reduces genetic gain.
• Insect and diseases can be reduced by maintaining tree vigour,
removing old cones (sanitation) and by orchard siting.
Conduct a ‘seed need analysis’ for all species and
populations (provenances) within your operating area.
Maintain a 5-10 year seed supply in a secure location.
Seed production from orchards is more consistent year to
year than from wild stands, so less storage is needed.
Consider all propagule sources including: improved (‘Class
A’) seed, vegetative cuttings, emblings, wild (‘Class B’ and
‘B+ seed’).
Use the best source first during inventory withdrawals.
Principles of seed inventory
Example seed need
calculation:
(a hectolitre is 100 litres)
Evaluate wild stands of the appropriate provenances for a
potential seed collection when seed inventories drop below
a 5-10 year supply.
This evaluation begins with ‘cone crop forecasting’ and is
followed by ‘crop monitoring’.
For 2 year cycle species, forecast next fall’s crop during the
previous winter by bud sampling:
• Collect a branch from the cone producing region of the crown for
several mature dominants/codominants in the stand.
• Count the female and vegetative buds for 3 internodes in from the
branch tip.
• A higher ratio of female:vegetative buds means a greater potential
crop (e.g. for Fd >0.2 indicates medium+ crop).
What is an easier way to forecast next fall’s crop for Yc and
pines (3 year cycle)?
Fd
Crop monitoring occurs in three phases: cone crop rating,
seed crop evaluation, seed maturity/pest monitoring.
Cone crop rating - cone crops are rated by examining the
cone producing region of the crowns of trees in suitable wild
stands during mid-summer of the collection year.
Suitable stands are healthy productive stands accessible for
monitoring and by the proposed means of collection.
Cone crops are rated as follows:
Once cone crop rating indicates a potentially collectible
crop, ‘seed crop evaluation’ is used to evaluate the quantity,
quality, maturity and overall condition of seeds within the
cones.
• A sample of cones is collected from the cone producing crown of good
quality parent trees via climbing, helicopter clipping or shooting.
• The cones are cut in half along the axis and the number of filled seeds
on the face of the cut is counted.
• Filled seeds contain healthy megagametophyte (storage tissue).
The crop is then monitored for maturity from mid-August
until the collection date, by sampling cones, observing their
colour and health, and cutting seeds to monitor embryo and
megagametophyte development.
Seeds are mature when:
• the embryo fills 90% of the embryo cavity
• the megagametophyte is firm and does not shrink
overnight at room temperature
• the cone begins to turn golden brown.
At maturity, the cone scales reflex (or shed in Abies).
Seeds of most species are shed within 2 weeks of maturity.
Sound seeds are the first to disperse.
It is critical to collect cones when they are just
approaching maturity and prior to commencement of
seedfall.
Too early: Too late:
When should serotinous lodgepole pine cones be collected?
There are numerous animal, bird and insect seed predators,
and fungal pathogens which damage cones and seeds.
Damage is greatest when light seed years follow heavy
seed years. In some cases, the majority of the crop is lost
because large predator populations have increased.
Cones should not be collected from the ground or from
squirrel caches as they are likely to be infected with fungal
pathogens such as the seed or cold fungus (Caloscypha
fulgens).
Why else is it a bad idea to collect from squirrel caches?
Cones infested by insects such as cone moths (Barbara
spp.) or seed chalcids (Megastigmus spp.), or by cone
rusts (Chrysomyxa spp.) should be separated from the
rest of the collection. In seed orchards, old cones are
removed and disposed of.
Cone collection, interim storage, transport and extraction
Cones and seeds are fragile and should be handled with care
during collection, interim storage and transport.
Reforestation decisions depend on information about the
seed source, collection and storage history. Each collection is
assigned a ‘seedlot number’ prior to the collection. Cone
sacks and seed packages must be properly labelled and
inventoried.
Cone collection methods include:
• aerial raking or clipping
• felling
• climbing
To choose method consider:
• species, size, location on tree and branch
• crop size and quantity to be collected
• access to site and trees
• safety and efficiency
Choose parent trees with good phenotypes.
Avoid cones from lower crown which may have been self-
pollinated.
As cones are collected:
Monitor cone and seed quality for filled seed content, maturity,
insects and disease using cutting test.
Remove old cones, mouldy cones, debris and foliage before
bagging; loosely fill sacks to allow room for cone expansion
and movement to avoid case-hardening.
Label sacks on the inside and outside with the seedlot number.
It may be necessary to re-sack cones which were wet when
collected, or cones of hemlock, Abies, cedar and cypress
which are naturally moist.
Air dry at interim storage for 4+ weeks before shipping to
extractory:
• ventilated shed with
racks - often open sided
• cool, dry and shaded
• protected from rodents
• turn sacks weekly
• periodically check
seeds with cutting test.
Hemlock and cedar of low elevation provenances have
low dormancy and may germinate in the cones under
moist warm conditions. Therefore ship such collections for
immediate extraction without interim storage.
After interim storage, ship sacks to extractory in refrigerated
trucks at 5-10 C.
The objective of cone and seed processing at the extractory
is to produce pure, dewinged (for all but Cw, Cy), sound, dry
seed, packaged for storage.
The basic processing steps are indicated in the figure
below. Because of differences in cone and seed
properties, the treatments at each step vary for different
species.
Cone and seed processing regimes are matched to the
cone and seed characteristics of each species and
provenance.
Seed may be stored for several decades prior to use.
Successful storage depends on:
• low moisture content (4-10% by weight)
• low storage temperature (-5 to -17 C)
• packaging and storage to minimize mechanical damage.
• periodic testing of moisture content, purity and
germination capacity.
In BC seed for use on Crown Land is stored at the
BCMOF Tree Seed Centre in Surrey.
Seedlots and seed requests are tracked by the BCMOF
through the Seed Planning and Registry Information
System (SPAR).
Summary
High quality seeds are: sound, store well, and have a high capability
to produce healthy seedlings that are well adapted to the reforestation
site and meet product objectives.
Seeds for major commercial species are increasingly produced in
seed orchards established with parents or progeny from breeding
programs - but wild stand collections are still important.
Quality is higher and collection is cheaper during heavy cone crop
years.
Cones must be collected just before they mature and release seed.
Cones must be handled properly to enable maturation and avoid
mould.
Monitoring, collection, handling and extraction procedures are
customized to reflect species differences.