Response to Selfing in Seed Set, Seedling Establishment and Nursery Growth Based on Controlled Crosses of Abies nordmanniana Clones

Nordmann fir (Abies nordmanniana) is used for production of high value Christmas trees in short rotation. Potentially all trees are intended to be sold - no thinnings are normally applied. A high proportion of saleable trees per ha is the main key to secure economic return to the growers. Consumers demand a symmetric and rather uniform tree and, dependent on local traditions, it should be more or less dense and narrow. In Denmark, breeding of Nordmann fir and establishment of seed orchards focus on seed supply and improved Christmas tree quality - aiming at adaption and a rather uniform ideotype Christmas tree. Benefits from employing rather few clones, to maximise gain and uniformity, may potentially be counteracted by increased selfing. The objective of this study was to quantify the effect of selfing on percentage of filled seed and nursery establishment of seedlings. Inbreeding depression was seen for filled seeds (40%), growth traits (5-17%), plus mortality and axial damage (5-12 percent units). Many selfed seedlings survive and develop into marketable seedlings, although with a depression in numbers of 23-37%, or 9-12 percent units. Nursery sorting procedures can only partially reduce the number of inbred seedlings in Nordmann fir. The large variation among clones in the response to selfing indicates that knowledge of the behaviour of selfed progeny from specific clones in ‘small number seed orchards’ is of practical interest. Trade-offs between increased gain by selection of few clones and a penalty paid for increased inbreeding need further studies during a full Christmas tree rotation.