Tree Genetics and Molecular Breeding 2024, Vol.14, No.2, 95-105 http://genbreedpublisher.com/index.php/tgmb 102 5.2 Disease resistance studies in trees In GWAS studies on disease resistance in certain tree species, genetic markers associated with the ability to resist specific pathogens have also been discovered. Younessi-Hamzekhanlu and Gailing (2022) used genome-wide association studies (GWAS) and quantitative trait locus (QTL) mapping to dissect disease resistance traits in forest trees (Figure 3). The study highlighted the potential of GWAS in identifying genetic markers associated with disease resistance, which is of great significance for forest tree breeding. By genotyping a large number of individuals, GWAS can precisely localize QTLs to individual genes based on linkage disequilibrium (LD) in unstructured populations. These genes are closely related to the disease resistance of trees, such as the NB-LRR, WRKY, bZIP, and MYB gene families and transcription factors. Furthermore, by integrating GWAS, QTL mapping, and genomic selection (GS) methods, the study proposed a strategy to accelerate the forest tree disease resistance breeding process. The GS method utilizes information from all genome-wide markers, regardless of their importance for a specific trait, to develop predictive models for individual performance. This finding not only provides a foundation for deepening the understanding of the genetic structure of disease resistance in forest trees but also demonstrates how to leverage genomic data to accelerate breeding programs and improve disease resistance in trees. Figure 3 Schematic representation of GWAS (a) and resulting Manhattan plot in forest trees for finding marker-trait associations in disease resistance studies (b) (Adopted from Younessi-Hamzekhanlu and Gailing, 2022) Image caption: On the x-axis of this plot, the markers are displayed on different chromosomes and on the y-axis, the –log10 p-values related to each marker are displayed. A threshold line is considered for p-values, and the SNP markers located above this line can be considered as potential QTL (Adopted from Younessi-Hamzekhanlu and Gailing, 2022) 5.3 Significance of GWAS research for ornamental tree variety improvement and breeding The research findings from GWAS provide strong genetic information to support the improvement of ornamental tree varieties. By identifying key genetic markers and genes, breeders can more effectively select or breed ornamental tree varieties with desirable aesthetic and adaptive traits. Utilizing the flower color-related genes discovered through GWAS, new varieties with specific flower colors can be bred through marker-assisted selection (MAS). Similarly, for adaptive traits such as drought tolerance or cold hardiness, GWAS results can guide targeted gene editing or selective breeding to cultivate tree varieties better adapted to local environmental conditions.
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