Genotype x trial interaction and stability across sites in 11 combined provenance and clone experiments with Picea abies in Denmark and Sweden

In 1997, eleven combined Picea abies (L.) Karst. provenance and clone trial s were assessed in two series, with identical genetic constitution and desi gn, in locations ranging from western Denmark to central Sweden, after 14 a nd 11 years, respectively. The phenotypic variation was larger for mixtures of 24 clones than for seedlings in one series, although 10 times more geno types were represented amongst the seedlings. This was explained by random C-effects due to propagation. Provenances of seedlings and clone mixtures w ere fairly stable across sites. Statistically significant clone x trial int eraction of growth traits were of the same magnitude as the clonal effects. The median genotypic correlation across sites for total height growth was 0.54. Ecovalence values for growth indicated that most clones contributed a bout equally to the interaction, with a tendency for clones with early bud break to give a larger contribution. Damage caused by late spring frost was assumed to be a main cause of genotype x environment interaction. Since in teractions relatively were more pronounced for growth increment than for th e latest height, the interaction seems to increase with age. Cluster analys is based on genotypic correlations between pairs of trials gave a very scat tered geographic pattern of the test sites. The results did not justify any suggestions for changes in the P. abies breeding strategy.