Transcript Frostavallen05F

Genetic diversity and seed
orchards
Dag Lindgren
2006-03-20
Uniform plantations
– a good thing?
Genetic diversity is a problem. A uniform crop:
• is easier to manage;
• is better paid;
• is preferred by customers;
• offers higher genetic gain.
Genetic diversity could be
favourable for biomass
production!
• A single genotype requests the same thing at the
same time. A mixture may use the ecological
space more efficient;
• A disease or pest may adapt and spread faster in
a uniform crop;
• If one genetic component fails, another may take
over the free ecological space in a diverse crop;
• A genetic diverse crop probably has a more
stable production over a range of environments,
is more repeatable and fails more seldom;
Genetic diversity is profitable
and politically correct
• Genetic diversity is politically correct and good
PR.
• Genetic diversity facilitates green certification
which has market value.
• Genetic diversity results in immediate
economical return as it improves sales.
• It is likely e.g. some spider species can be
identified which marginally benefits from
genetically diverse trees within species.
Perhaps too much diversity in
natural stands to constitute good
seed sources for planting?
• In nature only one seed among a million
develops into a mature tree. Room for
“natural selection” to improve the trees;
• Forestry plants in wide spacing and avoids
pre-commercial thinning. Most seeds
become planted seedlings and many planted
seedlings become valuable trees;
• Therefore the natural genetic diversity may
be unpractical large for modern forestry.
• People fear monoclonal GMO forests! This
fear is irrelevant for seed orchards.
• However, seed orchards are less efficient
than they could, as they are not a fancy
futuristic research priority.
How are seed orchard crops
different from “natural seeds”?
•
•
•
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Physiologically better seeds;
Parents are selected;
Little mating among relatives;
Other ramets of the same clone
cause selfing;
• Better defined and more
reproducible.
Suggested seed orchard impact
• A limited number of plus trees will get a
lot of descendents;
• The trees in the future forest will be
similar;
• The forest will grow faster.
The most important impact of seed
orchards on environment and
diversity is more productive forests!
• Intensive forestry causes environmental impact, not the
diversity of seed orchard crops!;
• Intensive forestry uses the site efficiently, thus less room
for others;
• If genetic diversity makes forests more fail-safe, that
strengthens the environmental impact of intensive
forestry;
• Much of the impact of the intensive forestry could be
positive. Productive profitable forests facilitates creating
reserves and financing environmental actions; forests
sequester carbon dioxide; forestry can be seen as
sustainable recycling of water and air;
• Improved material is an important component for
intensive forestry. Seed orchards stimulate more
intensive forestry!
Seed orchards have yet little
impact on Sweden
• 50 % of planted spruces and 80 % of planted pines are
from seed orchards;
• Some area never regenerated on purpose (15%?);
• Intentional ”Natural” regeneration 35%;
• Natural ”volunteers” in plantations (20%?);
• Many fathers unknown (40-50%);
• Only 1/3 of the genes in the forests established 2005 are
from selected trees
• The average age of a forest at final harvest is 110 years
and seed orchards have been important only for 30
years.
• As seed orchards has little impact on forest, they also
have low impact on genetic diversity.
Genetic diversity is the
backbone of evolution !
Source: Wei 1995
But this is irrelevant! Seed orchard crops are not central for evolution,
they are more or less planned as dead-ends. The long term breeding
is more important for the far future.
Rare gene variants can have a role in evolution, but not in production!
Variance in sample
Variance among few
catches most of all variance
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0.7
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0.1
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Sample Size
A small sample is as variable as the full population!
Seed orchard crops are diverse!
•Phenotypic selection of plus trees uncertain, preserves
diversity;
•Marker gene measurements indicate that seed orchard crops
can be more diverse than stand seeds;
•In a small piece of a natural forest, trees are as related as trees
from a seed orchard plantation;
•Seed orchard clones are recruited from a large area, which
favours diversity compared to stands;
•Pollen sources outside the seed orchard favours diversity;
•There are many clones in the current seed orchards;
•Thus a stand from a seed orchard is as diverse as a natural
stand!
Scots pine seed orchard; Suokanta,
Finland
Utilization
area
Locations
of the plus
trees
Location of
the seed
orchard
The new orchards
Modern seed orchards will be different from old:
• Selections will be tested and consider
performance of relatives (progeny), thus have
known breeding value;
• Fewer clones will be selected;
• I will discuss suitable clone number below;
• Relatives will be selected, but to a neglectable
extent.
Seed orchards with selected tested
clones
The best clones will be similar in estimated breeding value for the
selection criteria, that does not mean they will be very similar;
• The selection index selected for is a combination of characters, the
individual characters will be more different than the selection index;
• Selection based on young performance, selections will be more
different both earlier and later;
• Different batches of selections tested under different conditions will be
combined;
• One quarter of the parents to the seeds not in orchard;
• Even if characters look similar, the “cause” is probably different genes
in different trees;
• Just a few economically important characters affected by selection;
• Most of the genome will be unaffected;
• The reduction is just for BV, not for e.g. dominance;
• Most of the initial variance is recovered at mating, thus loss by
selection of parents has limited importance for their progeny;
• My guess is that the variance in future seed orchard crops will be at
least as wide as in current stand seeds even for economically
important factors.
Impact on landscape
Current Swedish plans extrapolated a century ahead may
lead to landscapes, where gene mass origin from few
ancestor trees. An educated guess…..
Share of gene mass
20%
20%
20%
40%
Ancestor trees
10
+20
+100
millions
Number of clones in a seed orchard
The most common agenda when talking about
genetic diversity or discussing legal constraints
Number of clones in current seed
orchards (source: Kang et al 2001)
Country
Species
Finland
P sylvestris
P abies
P sylvestris
P abies
P koraiensis
P densiflora
Sweden
Korea
Average
Number of
Clones
137
75
80
71
70
94
Current seed orchards has many clones
There were reasons to use many clones in seed
orchards until now:
• The plus trees was selected based on their
appearance in the forest and differ little in expected
breeding value;
• Its easier to get support for selecting plus trees and
testing clones if they are in seed orchards. Many
clones in seed orchards helped to get tree breeding
financed;
• More plus trees means more material for production
of grafts;
• Seed orchards functioned as clonal archives;
• Many clones reduces selfing and appears safe;
• Sometimes genetic thinning was planned.
Pines orchards in south US
(McKeand et al. 2003)
• Rough average:
–24 clones in lob SO;
–42 clones in slash SO;
• 6 SO with only 5-10 clones.
Optimal number study
Lindgren and Prescher (2005)
Considered factors:
• Genetic gain
• Genetic diversity
• Reasonable variations in ramet number and
fertility
• Pollen inflow (pollen contamination)
• Selfing
Swedish pine and estimates used unless
something else stated!
Selection Gain
Fewer clones → higher gain!
0.0
0.2
0.4
0.6
Proportion selected
0.8
1.0
Gain and gene diversity are in conflict!
Gain
Diversity
0
20
40
60
Number of clones
80
Positive diversity
• Diversity is assigned a positive value.
How to put a value on diversity?
Observations:
1. Mixes of agricultural lines are on average a few
percent superior to pure lines!
2. 59% of all loblolly in the US is deployed as half sib
family blocks and no problems are reported (McKeand et
al. 2003)!
3. Full sibs in many experiments and some forestry, few
problems reported!
4. Monoclonal plots in many experiments and some
clonal forestry, few problems reported for non extreme
cases.
A disadvantage in the magnitude 10% would be noticed
and reported for cases 2-4. The absence of many and
substantial reports supports a bound for the impact of
diversity.
Selfing
• Selfing becomes an important consideration
if there are few clones;
• A reason for a high clone number!
• Selfing can be slightly reduced if ramets of
the same clone are not placed adjacent.
Number of clones - results
• Swedish scenario: optimal number 16;
• Rather robust, thus 12 or 25 is not critical;
• Too few is more risky than too many. Safety bids 20 (example of “risk”:
pollen contamination problem solved);
• The estimates may be slightly conservative, perhaps revised to 12 in
some decades;
• It is tolerable with 10, but a higher number is probably better.
• Too high for production may still be right for “economy”!
• Future seed orchards will use clones in intentional different
proportions (more of the better), in that situation a slightly higher clone
number (25) can be used.
• American P taeda scenario gave optimal clone number 8 (more reliable
field testing and much experience of half sib forestry.
More?
More about the subject can be found by browsing:
http://www.genfys.slu.se/staff/dagl/
Dag Lindgren’s email is [email protected]
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