Genetic Correlations Among Field Trials of Norway Spruce Clones Representing Different Propagation Cycles

Serial cutting propagation means that clones are produced in consecutive propagation cycles, where a new round of cuttings are taken from the previously rooted cuttings, etc. The objective of this study was to judge the importance of propagation cycle on height growth in field trials. In a field trial series with Norway spruce clones, comprising nine trials in four cutting propagation cycles, propagation cycle only had a minor effect on height growth compared to the site effect. For inter-site correlation models where all trials were included, the best fit was obtained by an unstructured model, while the most parsimonious model included constraints on the correlations depending on cycle structure. Model constraints based on grouping of the trials by site productivity did not improve the fit. Testing for generally good performers over a range of different site conditions appears to be a good approach, unless drivers of genotype by environment interaction can be identified.