Genetic diversity and seed orchards

1
Genetic diversity and seed orchards

• Dag Lindgren
• 2006-03-20

2
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.

3
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

4
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.

5
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.

6

• 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.

7
How are seed orchard crops different from
natural seeds?

• Physiologically better seeds
• Parents are selected
• Little mating among relatives
• Other ramets of the same clone cause selfing
• Better defined and more reproducible.

8
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.

9
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!

10
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.

11
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!
12
Variance among few catches most of all variance
A small sample is as variable as the full
population!
13
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!

14
Scots pine seed orchard Suokanta, Finland
Locations of the plus trees
Utilization area
Location of the seed orchard
15
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.

16
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.

17
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 Ancestor trees
20 10
20 20
20 100
40 millions
18
Number of clones in a seed orchard

• The most common agenda when talking about genetic
  diversity or discussing legal constraints

19
Number of clones in current seed orchards
(source Kang et al 2001)
Country Species Average Number of Clones
Finland P sylvestris 137
P abies 75
Sweden P sylvestris 80
P abies 71
Korea P koraiensis 70
P densiflora 94
20
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.

21
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.

22
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!

23
Fewer clones ? higher gain!
24
Gain and gene diversity are in conflict!
25
Positive diversity

• Diversity is assigned a positive value.

26
How to put a value on diversity?

• Observations
• Mixes of agricultural lines are on average a few
  percent superior to pure lines!
• 59 of all loblolly in the US is deployed as
  half sib family blocks and no problems are
  reported (McKeand et al. 2003)!
• Full sibs in many experiments and some forestry,
  few problems reported!
• 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.

27
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.

28
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.

29
More?
More about the subject can be found by browsing
http//www.genfys.slu.se/staff/dagl/ Dag
Lindgrens email is Dag.Lindgren_at_genfys.slu.se
30
End..,