COMBINING GENETIC GAIN AND DIVERSITY BY CONSIDERING AVERAGE COANCESTRY IN CLONAL SELECTION OF NORWAY SPRUCE

Genetic relationship within a population can be measured by average co ancestry. This can also be expressed as an effective number which repr esents the relative genetic diversity of the population. The goal of b reeding can be formulated to maximise genetic value minus average coan cestry times a constant (the ''penalty constant''). An iterative searc h algorithm can then be used to find the best selections for meeting t his goal. Two such algorithms, one for a fixed number of selections an d the other for a variable optimum number, were applied to select a mi xture of field-tested Norway spruce clones with known parents. The res ults were compared with those from the conventional method of restrict ing parental contributions to the selected population as a means to co ntrol diversity. Coancestry-adjusted selection always yielded more gai n than restricted selection at a given effective population size (exce pt under circumstances where the methods were equivalent). Expressed a nother way, at any given level of gain, coancestry-adjusted selection maintained a larger effective population size than did restricted sele ction. The relative superiority of coancestry-adjusted selection decli ned when the effective population size approached the lowest value. th at at which no penalty or restriction was applied. The method was exte nded by the second search algorithm to optimise the selected number of clones. The optimal number of clones can be rather large when diversi ty is heavily valued, but the reduction in genetic gain becomes large.