Stratified sublining

1. 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)

3. Rank tested founders for breeding value; • Mate adjacent founders (Single Pair Mating, Positive Assortative Mating); • Testindividual offspring for breeding value; • Select two best tested offspring in each family; • Rank these pairs; • Mate the adjacent offspring pairs (best with best and second best with second best).

4. Rank tested founders for breeding value; • Mate adjacent founders (Single Pair Mating, Positive Assortative Mating); • Testindividual offspring for breeding value; • Select two best tested offspring in each family; • Rank these pairs; • 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.

5. 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

6. 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 >15%. • Guarantee that good unrelated selections can be made from the recruitment population.

8. 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!

9. 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.

10. 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.

11. 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.

12. 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

13. 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.

14. Later generations? Non inbred F2, but inbreeding can only be delyed, not prevented. Inbreeding above > 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!

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

16. References • Ruotsalainen S & Lindgren D 2001 Number of founders for a breeding population using variable parental contribution. Forest Genetics 8:59-68. • Ruotsalainen S & Lindgren D 2000 Stratified sublining: a new option for structuring breeding populations Canadian Journal of Forest Research. 30: (4) 596-604