Page 41 - University of Pretoria RESEARCH REVIEW 2018

A major advance in the past year has been the establishment of a Genome Diversity Atlas for Eucalyptus and pine tree species grown in South Africa. Another outcome is an international effort in collaboration with North Carolina State University and the University of Connecticut to generate a DNA chip with 50 000 genome-wide markers for tropical pine species grown in southern Africa and South America. This resource will be useful for gene conservation and molecular breeding of pine trees, which has previously been difficult due to the large size of the pine genome (>20 billion bp, seven times larger than the human genome).
Climate change is expected to have major impacts on forestry operations in South Africa, in some cases requiring a complete shift in planted tree species. Genomic technologies can now be combined with spatial technologies such as remote sensing and climate modelling to understand the adaptation of forest trees to changing environments. The FMG team has embarked on this emerging field called landscape genomics
to predict tree genotypes that are best adapted to current and future environments. The team initiated
a landscape genomics study for Eucalyptus grandis trees and mapped novel genomic variation available
for this species in its natural range
in Australia that can be deployed for sustainable forestry in South Africa.
Most commercially important traits are quantitative in nature and affected by hundreds of genes throughout the genome. Genome-wide DNA marker analysis has proven to be a powerful tool for tracking this genetic variation and developing predictive models of the breeding values of individual trees. Professor Myburg’s team has used a single nucleotide polymorphism (SNP) marker chip with 60 000 DNA markers to produce genome profiles for over
4 000 Eucalyptus trees in order rapidly to dissect complex traits in these trees. They are collaborating with researchers in Sappi and Mondi to
develop and apply Genomic Selection as a novel tree breeding approach.
Adding molecular traits such as
gene expression variation in tree populations allow systems genetics modelling to provide further biological insight into the molecular basis of complex trait variation. In collaboration with Eshchar Mizrachi, the FMG
team has applied systems genetics approaches to dissect secondary
cell wall (wood property) traits in Eucalyptus. MSc student Martin Wierzbicki has used this approach
to perform the most comprehensive systems analysis of the genetic control of hemi-cellulose (xylan) biosynthesis in a forest tree to date.
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