Assessing the potential for assisted gene flow using past introduction of Norway spruce in southern Sweden: Local adaptation and genetic basis of quantitative traits in trees

Abstract

Norway spruce (Picea abies) is a dominant conifer species of major economic importance in northern Europe. Extensive breeding programs were established to improve phenotypic traits of economic interest. In southern Sweden, seeds used to create progeny tests were collected on about 3,000 trees of outstanding phenotype (‘plus’ trees) across the region. In a companion paper, we showed that some were of local origin but many were recent introductions from the rest of the natural range. The mixed origin of the trees together with partial sequencing of the exome of >1,500 of these trees and phenotypic data retrieved from the Swedish breeding program offered a unique opportunity to dissect the genetic basis of local adaptation of three quantitative traits (height, diameter and bud‐burst) and assess the potential of assisted gene flow. Through a combination of multivariate analyses and genome‐wide association studies, we showed that there was a very strong effect of geographical origin on growth (height and diameter) and phenology (bud‐burst) with trees from southern origins outperforming local provenances. Association studies revealed that growth traits were highly polygenic and bud‐burst somewhat less. Hence, our results suggest that assisted gene flow and genomic selection approaches could help to alleviate the effect of climate change on P. abies breeding programs in Sweden.

Divergent patterns between phenotypic and genetic variation in Scots pine

“…If we account for the marker-estimated heritability of 0.56, which is somewhat higher than previously reported, the global phenotypic differentiation would be even higher, Q ST = 0.9 (95% HPDI 0.65–0.97, see Materials and methods ). High Q ST values for phenology-related traits have also been reported for other tree species, e.g., Norway spruce ( Milesi et al., 2019 ), downy birch ( Bennie et al., 2010 ), European beech ( Strømme et al., 2019 ), and European aspen ( Hall et al., 2007 ). Analysis of phenotype–environment associations with 68 climate variables identified mainly those that describe the temperature over the year, GDD5, GDD0, bio01, and latitude.…”

“…A global F ST of 0.0037 is much lower than that in Norway spruce ( Picea abies ), which also has a large distribution and a postglacial migration history similar to that of Scots pine. In Norway spruce, strong genetic differentiation is observed between the northern and the central parts of Europe ( F ST = 0.15–0.22; Chen et al., 2019 ; Milesi et al., 2019 ), as well as at a regional scale in northern Europe ( Tollefsrud et al., 2009 ; Tsuda et al., 2016 ; Li, 2020 ; Sullivan, 2020 ). Our observation of weaker population structure in Scots pine in northern Europe, with no distinct subgroups, is in accordance with previous studies of Scots pine population structure ( Dvornyk et al., 2002 ; Pyhäjärvi et al., 2007 ; Zimmer and Sønstebø, 2018 ; Tyrmi et al., 2020 ).…”

Clinal variation in growth cessation and FTL2 expression in Siberian spruce

“…On the other hand, as alluded to in the "Introduction," there are strong inherent limits to the dissection of quantitative adaptive traits such as growth cessation. In a genome-wide association study based on 1500 spruce trees from Southern Sweden, we found that 32 SNPs belonging to 15 transcripts were associated to variation in budburst, an important phenology trait, which is primarily controlled by temperature (Milesi et al 2019). While budburst was less polygenic than height or diameter (131 and 138 transcripts associated to trait variation, respectively), it still appears as a very polygenic trait.…”

“…Strikingly, studies in both conifers and angiosperms have pointed to the same group of genes, so far mostly genes from the photoperiodic pathway, in particular FT-Like genes, suggesting that the same mechanism may be at work in groups of plants that have diverged hundreds of million years ago. In Norway spruce, the availability of thousands of polymorphisms across the genome of thousands of individuals from the Swedish breeding program, together with similar data from latitudinal and longitudinal clines, offers a unique opportunity to obtain a better understanding of the genetic basis of local adaptation to latitude and assess the potential of assisted migration to counter the effect of climate change (Aitken and Whitlock 2013;Milesi et al 2019). On the other hand, as alluded to in the "Introduction," there are strong inherent limits to the dissection of quantitative adaptive traits such as growth cessation.…”

Climate Change Synchronizes Growth and iWUE Across Species in a Temperate-Submediterranean Mixed Oak Forest

“…Genotypic changes take place through gene frequency changes across generations and are slower than phenotypic changes (Alberto et al, 2013). Although local adaptation (Kawecki and Ebert, 2004) is more common in trees than in some other non-woody plant species, the long generation and residence times in the same environment challenges tree survival under rapid and abrupt changes in climate (Savolainen et al, 2007). However, the long life-span of trees provides a wealth of information on the evolutionary phenotypic adjustments to environmental changes using subrogates from which past adaptation of trees to climate changes can be inferred (e.g., Fritts, 1976).…”