475
trees combining phenotypic, pedigree and marker information and for the evaluation of the accuracy of the predicted breeding values (Cappa et al. unpublished data).
The use of SSR markers in Nothofagus also allowed to determine (1) restricted
gene flow distance (<45 m) and significant seed and pollen immigration for continuous forests of N. obliqua and N. alpina, (2) the influence of tree size (DBH and
height) on female and/or male fertility and (3) the occurrence of significant finescale spatial genetic structure (FSGS), which is consistent with the restricted seed
and pollen dispersal (Sola et al. 2020). All this knowledge has several implications
both for understanding the evolution of the species and for breeding actions. For
example, significant FSGS suggests that, for future ex situ conservation, restoration
and breeding strategies, seeds need to be collected from selected mothers belonging
to different genetic clusters at a distance >45 m to avoid collecting seeds from
genetically related individuals.
Collections of annotated genes have been used to select 25 candidate genes (CG)
related to water stress responses in order to characterize their genetic variation
along a precipitation gradient and to identify putative adaptive molecular markers
for Nothofagus species (Soliani et al. 2020). The study revealed (1) moderate SNP
diversity within and between N. alpina and N. obliqua; (2) higher nucleotide and
haplotype diversity in N. obliqua than in N. alpina, consistently with the results
obtained by El Mujtar et al. (2014) using SSRs; (3) different patterns of variation
along a precipitation gradient, with higher diversity at the east (lower precipitation)
for N. alpina and at the west (higher precipitation) for N. obliqua; (4) signal of balancing selection in two populations of N. obliqua at one CG; and (5) a similar pattern for N. pumilio with moderate nucleotide and haplotype diversity and higher
diversity in western population. The screening of functional SSR markers for the
same species (and gradients) revealed (1) genetic diversity trends differing between
species and showing an opposite pattern of variation with respect to the CGs, being
correlated with mean annual precipitation only in N. alpina and (2) signal of balancing or positive selection for some SSRs. These results provide preliminary evidence
of gene regions functionally related to key responses of trees inhabiting environmental gradients.
On the other hand, although the capacity to apply massive genotyping to native
forest tree species exists in Argentina, its application is yet scarce mostly due to the
high costs involved. Nothofagus species are perhaps the exception, as massive genotyping has been used or is being included on research projects on species of the
genus. Hasbún et al. (2016) using GBS investigated more than 10K SNP loci in
Chilean N. dombeyi populations, revealing that genome-wide patterns of genetic
diversity and differentiation varied widely across the genome. The study allowed
the identification of numerous genomic regions exhibiting signatures of divergent
selection and provided strong evidence of substantial genetic differentiation associated with both temperature and precipitation gradients, suggesting local adaptation.
This strategy is also being used in N. dombeyi populations of Argentina to detect
genomic markers associated to drought response (Fasanella et al. 2019). Three other
projects focused on phenotype-genotype association studies will perform massive
genotyping (RADSeq, GBS and exome capture) for common garden, populations of
17 Application of High-Throughput Sequencing Technologies in Native Forest Tree…
trees combining phenotypic, pedigree and marker information and for the evaluation of the accuracy of the predicted breeding values (Cappa et al. unpublished data).
The use of SSR markers in Nothofagus also allowed to determine (1) restricted
gene flow distance (<45 m) and significant seed and pollen immigration for continuous forests of N. obliqua and N. alpina, (2) the influence of tree size (DBH and
height) on female and/or male fertility and (3) the occurrence of significant finescale spatial genetic structure (FSGS), which is consistent with the restricted seed
and pollen dispersal (Sola et al. 2020). All this knowledge has several implications
both for understanding the evolution of the species and for breeding actions. For
example, significant FSGS suggests that, for future ex situ conservation, restoration
and breeding strategies, seeds need to be collected from selected mothers belonging
to different genetic clusters at a distance >45 m to avoid collecting seeds from
genetically related individuals.
Collections of annotated genes have been used to select 25 candidate genes (CG)
related to water stress responses in order to characterize their genetic variation
along a precipitation gradient and to identify putative adaptive molecular markers
for Nothofagus species (Soliani et al. 2020). The study revealed (1) moderate SNP
diversity within and between N. alpina and N. obliqua; (2) higher nucleotide and
haplotype diversity in N. obliqua than in N. alpina, consistently with the results
obtained by El Mujtar et al. (2014) using SSRs; (3) different patterns of variation
along a precipitation gradient, with higher diversity at the east (lower precipitation)
for N. alpina and at the west (higher precipitation) for N. obliqua; (4) signal of balancing selection in two populations of N. obliqua at one CG; and (5) a similar pattern for N. pumilio with moderate nucleotide and haplotype diversity and higher
diversity in western population. The screening of functional SSR markers for the
same species (and gradients) revealed (1) genetic diversity trends differing between
species and showing an opposite pattern of variation with respect to the CGs, being
correlated with mean annual precipitation only in N. alpina and (2) signal of balancing or positive selection for some SSRs. These results provide preliminary evidence
of gene regions functionally related to key responses of trees inhabiting environmental gradients.
On the other hand, although the capacity to apply massive genotyping to native
forest tree species exists in Argentina, its application is yet scarce mostly due to the
high costs involved. Nothofagus species are perhaps the exception, as massive genotyping has been used or is being included on research projects on species of the
genus. Hasbún et al. (2016) using GBS investigated more than 10K SNP loci in
Chilean N. dombeyi populations, revealing that genome-wide patterns of genetic
diversity and differentiation varied widely across the genome. The study allowed
the identification of numerous genomic regions exhibiting signatures of divergent
selection and provided strong evidence of substantial genetic differentiation associated with both temperature and precipitation gradients, suggesting local adaptation.
This strategy is also being used in N. dombeyi populations of Argentina to detect
genomic markers associated to drought response (Fasanella et al. 2019). Three other
projects focused on phenotype-genotype association studies will perform massive
genotyping (RADSeq, GBS and exome capture) for common garden, populations of
17 Application of High-Throughput Sequencing Technologies in Native Forest Tree…