No abstract

The aim of this study was to analyze and compare the performance of Norway spruce seed sources from Swedish stands of East European origin (SweEast) with material from Swedish (SweSO) and East European (EastSO) seed orchards, and with material from Swedish (SweS) and East European (EastS) unimproved stands. The seed sources were field tested at six locations in southern Sweden and assessed for growth and phenology. The assessment of growth traits indicated that trees from SweSO and EastSO had 9-15% greater growth with respect to tree height and diameter in comparison to trees from Swedish local unimproved stands (SweS). Trees from SweEast and EastS showed around 5-7% greater growth. With respect to phenological traits, the expected later bud burst for EastS and EastSO in comparison to SweS, SweSO and SweEast was verified. However, SweEast exhibited earlier bud burst compared to EastS than what could be explained by pollination by Swedish pollen. This was explained by early land race formation for that trait. A strong positive correlation was observed between bud burst and frost damage, which indicates that earlier bud burst does indeed increase the risk of damage from late spring frost at frost-prone sites.

The summer drought of 2018 was one of the most climatically severe events in Europe that led to record-breaking temperatures and wildfires in many parts of Europe. The main objective of this study was to assess the impact of the 2018 drought on the phenotypic and genetic response of Norway spruce height growth using the Standardized Precipitation-Evapotranspiration Index (SPEI). To achieve this, the total cumulative height growth of about 6000 clones from 2016 to 2019 in four full-sib trials in Sweden, aged 6–7 years, and from 2017 to 2019 in two half-sib trials in Finland, aged 8–9 years, were measured. The results indicate that the 2018 drought caused reductions in the increment of trees. Although heritability estimates were similar to other reports for Norway spruce, the additive genetic variance was highly inflated in one of the visibly drought-damaged trials in Southern Sweden. Similarly, the genotype by environment (G × E) interaction was highly significant in the drought-damaged Southern Swedish trials. Both additive genetic and phenotypic correlations obtained between height increments in 2019 and final heights were the weakest in all studied trials, implying that the drought legacies might have influenced the recovery of trees in 2019. We may conclude that the severe drought can be an underlying factor for a strong G × E interaction and changes in the ranking of genotypes. Therefore, a selection of drought-resistant genotypes with a good growth capacity tested in variables sites should be considered as an important criterion for future breeding of Norway spruce.