Diallel crosses in Picea abies III. Variation and inheritance patterns in nursery trials

The complete diallel cross is the only mating design that provides estimates of variance components of general combining (GCA), specific combining ability (SCA), maternal and reciprocal effects, in addition to heritabilities and genetic correlations. To obtain such estimates, complete diallels were made among 10 trees in each of three natural Norway spruce populations from altitude 300 and 500 m in Norway. Nursery trials were performed with the families from these crosses and families from seeds collected from open pollination. Traits measured and analysed are seed weight, germination rate, germination percentage, terminal bud set, and seedling heights the first and second years. The seedlings from the population at origin 500 m had lower seed weight, lower heights and earlier bud set than those from the two populations from lower altitude. A considerable variation was present among families within each diallel, and the GCA variance components had the highest values and were significant for most traits. Variance components for SCA and maternal effects were also significant for some traits, but with inconsistent values in the three diallels. A strong relationship was present between the weight of the seed lots from the maternal parent and mean family height after one and two growing seasons. The highest estimate of heritability was observed for bud set, with similar values in all three diallels.