How can genomic selection contribute to improving breeding of forest trees? In the research project of Pilar Herrera Egoavil, genetic approaches are used to shorten the breeding cycle for silver birch.
Pilar Herrera Egoavil, PhD student at Uppsala University and affiliated with Trees For Me, explains that the primary goal of genomic selection is to make it progressively easier to select trees with desirable characteristics based only on their genetic information, thus improving breeding efficiency. This technique allows for choosing the best trees at the genetic level and an early age, speeding up the breeding cycle. Thus, breeders can identify promising trees much earlier instead of waiting for the grown up trees to show the desirable characteristics.
“This is especially important for tree breeding, where many genes and environmental factors often influence long breeding cycles and the complexity of tree traits, thus presenting unique challenges. Genomic selection enables us to use a dense panel of genetic information to predict physical characteristics of interest (e.g. wood density), with the help of advanced genetics and statistical tools, making it a powerful solution to implement for modern tree breeding programmes”, says Pilar Herrera Egoavil, who below describes the work in the research project in more detail.
The intersection of natural history and tree breeding
Pilar Herrera Egoavil explains that during the Last Glacial Maximum (around 18,000 years ago), species in Europe retreated to “refugia,” areas where populations of organisms survived periods of unfavourable conditions. As reported in many studies, most of these refugia were located south or east of the ice sheet in Europe. Once the environment improved and the ice sheet disappeared, organisms from different refugia expanded to northern Europe, meeting in large “contact zones”, like the one in central Scandinavia, which runs from east to west across the peninsula.
In her current research, Pilar Herrera Egoavil is conducting a comparative study of the contact zone in central Scandinavia for three key forest tree species: Betula pendula (Silver birch), Picea abies (Norway spruce) and Pinus sylvestris (Scots pine).
“The study of contact zones of the different tree species provides valuable insights into the unique genetic composition and structure of the tree populations (population structure), the mechanisms maintaining their genetic diversity, and the barriers to the movement of genetic material between different tree populations, also known as gene flow. Understanding the population structure of these species is vital to avoid false positives in genome-wide association studies and improve the efficiency of genomic selection”, says Pilar Herrera Egoavil.
The research findings so far show that each species studied has two main genetic groups in Sweden, located in the northern and southern regions. These two main genetic groups of each species meet at the transition between the two major climatic zones in Sweden and this is assumed to be the “contact zone”. Ongoing analyses will determine whether these populations are locally adapted to their environments, as is usually observed in tree species.
“These results are crucial for silver birch breeding because they confirm previous observations and will guide the establishment of genomic selection breeding populations in Sweden. They will ensure the selection of genotypes best suited to specific environments,” says Pilar Herrera Egoavil.
Knowing the genetic diversity of silver birch
In the early stages of Pilar’s project, she also obtained over 600 whole genome sequences from silver birch trees. This dataset covers a wide latitudinal range of the silver birch natural populations across Sweden. Additionally, it has been complemented by silver birch populations in Eurasia and the closely related species Betula pubescens (downy birch) and Betula nana (dwarf birch). This dataset is crucial for studying the genetic diversity of silver birch in Sweden and across Eurasia, as well as for understanding the evolutionary and demographic processes that have shaped its genetic makeup.
“To begin with, I identified genetic variations that segregate within the natural range of B. pendula. In close collaboration with colleagues from Finland, we have developed a common list of genetic variations from our combined datasets. This dataset on genetic variations is being used to develop a genomic tool, which will be important for linking the genetic information with desirable tree traits in future studies”, Pilar Herrera Egoavil explains.
“We recently received the first results from our genomic tool. The next step is to sort the identified genetic variations into different groups (e.g. functional, neutral, etc). This sorting will be used in future genomic selection and evolutionary studies, allowing us to create a more efficient genotyping tool for breeding. This will enhance the accuracy and predictability of genomic selection, help group populations, and build pedigrees”, Pilar Herrera Egoavil concludes.
Glossary
- Genomics
The study of an organism's genome, its genetic material, and how that information is applied.
- Genomic selection
Genomic selection in tree breeding is a method that uses a large amount of genetic data to predict and select the best trees with desired traits, such as growth rate and wood quality. This selection can be done early in the tree’s lifecycle, speeding up the breeding process.
- Contact zone
A contact zone refers to geographic regions where distinct populations, species, or communities meet. These zones often reflect secondary contact between previously isolated flora and fauna, providing insights into unique population interactions.
- Genotype
An organism’s complete set of genes.
- Genome-wide association study (GWAS)
An observational study of a genome-wide set of genetic variants in different individuals to see if any variant is associated with a trait.