Stratified sublining

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Stratified sublining

• Dag Lindgren,
• Swedish University of Agricultural Sciences, 901
  83 UMEÅ, Sweden.
• Seppo Ruotsalainen,
• The Finnish Forest Research Institute, 58450
  Punkaharju, Finland.
• Matti Haapanen,
• The Finnish Forest Research Institute, 01301
  Vantaa, Finland.

Recipe for stratified sublining(Ruotsalainen and
Lindgren 2000)
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1. Rank tested founders for breeding value
2. Mate adjacent founders (Single Pair Mating,
   Positive Assortative Mating)
3. Test individual offspring for breeding value
4. Select two best tested offspring in each family
5. Rank these pairs
6. Mate the adjacent offspring pairs (best with best
   and second best with second best).

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1. Rank tested founders for breeding value
2. Mate adjacent founders (Single Pair Mating,
   Positive Assortative Mating)
3. Test individual offspring for breeding value
4. Select two best tested offspring in each family
5. Rank these pairs
6. Mate the adjacent offspring pairs (best with best
   and second best with second best).

Now stratified sublines have been formed.
F2-individuals in different sublines are not
related, individuals within sublines are either
full sibs or double first cousins. The sublines
are genetically stratified, the best genotype in
the subline is expected to be better the higher
rank the subline has.
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Now stratified F2-sublines have been formed.
F2-individuals in different sublines are not
related, individuals within sublines are either
full sibs or double first cousins. The sublines
are genetically stratified, the best genotype in
the subline is expected to be better the higher
rank the subline has. Stratified sublining
structures the breeding material according to its
quality, other similar concepts are

• Nucleus breeding
• Elite breeding
• Positive Assortative Mating
• Structuring in tiers

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Why stratified sublining?

• Better seed orchards!!!! The very best clones
  selected for seed orchards will be substantially
  better!!
• One generation ahead stratified lines are
  identical to PAM, the added gain to seed orchards
  (Rosvall 1999) is 15.
• Two generations ahead, compared with assortment
  to sublines by random, Ruotsalainen and Lindgren
  (2000) found superiority gt15.
• Guarantee that good unrelated selections can be
  made from the recruitment population.

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More advantages

• The superiority of the best families and family
  forestry will boosted!
• The advantage to allocate the families to the
  best sites will increase!
• The advantage of clonal forestry will be
  amplified!
• The advantage of the linear deployment technique
  (where the better clones are used in higher
  proportions) is considerable amplified!

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Advantage amplified if breeding effort dependent
on genetic value

• Such consideration could comprise size of
  breeding population per parent.
• Size of breeding population could be a matter of
  optimisation, not a central parameter for
  defining a breeding strategy!
• Thus, in the good sublines more selections for
  breeding could be done, resulting in more F2
  families.

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Carry on more genmass from the best founders and
less from medium (Ruotsalainen and Lindgren 2001)

• It seems possible to improve implementation of
  stratified lines.
• One remedy may be to let the best gene mass be
  present both in high and in low ranking lines,
  the latter anyway are less likely to be used for
  seed orchards in the near future.
• Another remedy is to use more founders to build
  the low ranking sublines.

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• Breeding population must be cycled by Single Pair
  Mating, that may sometimes be an advantage as the
  within family selection intensity is higher!
• E.g. Swedish program
• DPM from two families size 10,
• the best is selected, i 1.54.
• SPM from one family size 20,
• the top two are selected, i 1.64.

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Potential advantage of inbreeding in breeding can
be well managed in stratified lines

• Fuller use of the genomes of the best founders
• Widens the variance among lines amplifies
  stratification advantage
• Inbreeding depression will decrease over the
  generations
• Selection within the best genomes with reduced
  coancestry increase

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Gene mass in the low ranking lines will probably
have little impact on the seed orchards in the
near future

• That is right, it is an insurance to changing
  demands and goals beyond the near future. For the
  same reasons breeders carry on larger and more
  diverse breeding populations than immediatly
  needed.
• Thus the advantage of stratified sublining is
  more important in the upper strata. Maybe only
  the top 60 of the effort should go to the
  topranking gene mass organised in stratified
  lines, how the gene mass is distributed in the
  bottom is less of a stratified sublining problem.

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Later generations?

• Non inbred F2, but inbreeding can only be delyed,
  not prevented. Inbreeding above gt 0.125 causes
  problems even if the production population is
  non-inbred.
• Options (examples)
• Lassaiz faire
• Refresh
• Merge into fewer unrelated stratified lines
• Merge all lines
• Use inbreeding as a tool.
• There exists many variants of options and
  suboptions, the long-term loss will be marginal
  if any, but the benefits the first generations is
  large!

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OP offspring, low rank line suggestion

1. Select superior OP families (in office). Rank the
   mothers for BV!
2. Select 6 phenotypically best trees from selected
   families (in field)
3. Create 6 full sibs by crossing selected trees
   from two families with adjacent ranks for BV!
4. Select 4 trees with assumed high BV for
   progeny-test
5. Select best tree with the founder mother trees as
   grandparents. That tree will be PAM mated and
   join a stratified line.
6. Or select two cousins, and mate them to the most
   adjacent pair of cousins from another similar
   construct

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References

• Ruotsalainen S Lindgren D 2001 Number of
  founders for a breeding population using variable
  parental contribution. Forest Genetics 859-68.
• Ruotsalainen S Lindgren D 2000 Stratified
  sublining a new option for structuring breeding
  populations Canadian Journal of Forest Research.
  30 (4) 596-604