A MODEL FOR INFUSION OF UNRELATED MATERIAL INTO A BREEDING POPULATION

A consequence of selection in a closed breeding population is an incre ased level of relatedness. One remedy to this may be infusion of unrel ated genetic material into the breeding population. A model is establi shed to study such infusion assuming that new plus-trees equivalent wi th the old are available. The model uses group merit as the criterion for balancing genetic gain and relatedness measured by group coancestr y. Infusion is optimized by finding the maximum group merit. The model involves variables such as average breeding value, structure (family number and size), heritability, relatedness (group coancestry) and its importance (penalty coefficient), and inbreeding. The most important determinant for infusion is the breeding value of the bred material fo llowed by the relatedness between the selected families. An example wi th considerable similarities to the Swedish breeding program of Norway spruce and Scots pine was given. For establishing the first generatio n breeding population, it seems optimal to add about 20% to 25% new pl us-tree selections rather than to make all selections in the progenies of the existing untested plus-trees. If the plus-trees were progeny t ested, about 5% to 10% new selection seems desirable. For more advance d generations, the desire of infusion depends on progress in breeding value and accumulation of relatedness and inbreeding in the breeding p opulation.