Triticeae Genomics and Genetics, 2024, Vol.15, No.3, 162-171 http://cropscipublisher.com/index.php/tgg 167 The principal component analysis shows the polymorphism across approximately 1,200 varieties, highlighting the significant reduction in genetic diversity among modern wheat varieties compared to wild relatives and landraces (Figure 2). Furthermore, the dendrogram in Figure 2b, depicting gene presence/absence variation (PAV) among different varieties, reveals the genetic similarities and differences, indicating how the narrowing of the genetic base may be attributed to selective pressures that fix specific advantageous genes while potentially losing others (Walkowiak et al., 2020). These visual analyses confirm how wheat genomes undergo genetic erosion under the influence of intensified selection and breeding practices, which is critical for developing future breeding strategies aimed at enhancing crop resilience and adaptability. Figure 2 Patterns of variation in the wheat genome (Adopted from Walkowiak et al., 2020) Image caption: a, Principal component analysis of polymorphisms from exome-capture sequencing of about 1,200 lines (grey markers), 16 lines from whole-genome shotgun resequencing (orange markers) and our new assemblies (black markers). Text colours reflect different geographical locations and winter or spring growth. b, Dendrogram of pairwise Jaccard similarities for gene PAV between all RQA assemblies. c, Number of unique NLRs at different per cent identity cut-offs as the number of genomes increases. Dashed vertical lines represent 90% of the NLR complement. Markers indicate the mean values of all permutations of the order of adding genomes. Whiskers show maximum and minimum values based on one million random permutations. d, Chromosomal location versus insertion age distribution of unique to (reading downward) increasingly shared syntenic full-length LTR retrotransposons (Adopted from Walkowiak et al., 2020) 6.1.2 Strategies to enhance genetic diversity To counteract genetic erosion, several strategies can be employed to enhance genetic diversity in wheat breeding. One effective approach is the utilization of synthetic hexaploid wheat (SHW), which is created by crossing tetraploid wheat with diploid wild relatives such as Aegilops tauschii. This method introduces new alleles and increases genetic recombination, thereby broadening the genetic base of wheat (Wan et al., 2020; Wan et al., 2023). Additionally, the incorporation of diverse germplasm from genebanks and the use of advanced genomic tools to identify and introgress beneficial alleles from wild relatives and landraces can further enhance genetic diversity (Aberkane et al., 2020; Sansaloni et al., 2020).
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