Genetics in and opportunities for improvement of Nordmann fir (Abies nordmanniana (Steven) Spach) Christmas tree production

Abstract

Christmas tree is an important specialty crop. In Europe, the main Christmas tree species is Nordmann fir (Abies nordmanniana (Steven) Spach) and nearly 42 million trees are sold each year. This paper focuses on three key traits for Christmas tree production: growth (including branching), commercial tree quality, and post-harvest needle retention. The objectives of the study are to estimate genetic variation and heritability, genotype-by-site interaction, and genetic correlations among traits, and to illustrate and discuss potential gains from selection. The field trial series comprises 10 sites, 7 provenances, and 128 single-tree open-pollinated offspring from five Danish seed sources (in total 45,531 trees). At year 7 from planting, growth and quality were assessed on all sites. A subset of three sites were sampled twice (in October and November) for evaluation of post-harvest needle retention. Heritabilities across sites were 0.23, 0.21, and 0.13 for tree height, number of branches, and Christmas tree score, respectively. Heritability for post-harvest needle retention increased from 0.28 in October to 0.55 in November. Average additive genetic site-by-site correlation for tree height was 0.72, for number of branches 0.86, and for Christmas tree score 0.72, indicating that the genotype-by-site interaction is small and not important. Post-harvest needle retention did not correlate to any other traits. Potential gains from backward selection and grafting superior plus-trees in clonal seed orchards, e.g. the 15–20 best ones, were estimated to be 20% in Christmas tree score, number of branches, and height, and 65% in November post-harvest needle retention.