Triticeae Genomics and Genetics, 2024, Vol.15, No.3, 152-161 http://cropscipublisher.com/index.php/tgg 155 Exotic germplasm often possesses complementary traits that are absent or rare in domestic varieties. For example, landraces from regions like Iraq, Iran, and India were found to harbor new allelic variations for vernalization and glutenin genes, which are valuable for breeding programs targeting specific environmental adaptations and quality traits (Upadhyay et al., 2020). Additionally, synthetic-derived wheat lines have been shown to contribute alleles that increase grain yield under various environmental conditions, outperforming elite parent cultivars. These complementary traits from exotic germplasm can be harnessed to improve the resilience and productivity of domestic wheat varieties. In summary, the assessment of genetic diversity in exotic germplasm through both morphological and molecular approaches reveals significant variability and novel traits that can be leveraged for wheat improvement. Comparing this diversity with domestic germplasm underscores the potential of exotic sources to enhance genetic variation and introduce complementary traits, thereby contributing to the development of superior wheat cultivars. 4 Utilization of Exotic Germplasm in Wheat Breeding 4.1 Successful case studies The introgression of exotic germplasm has been pivotal in enhancing disease resistance in wheat. For instance, the introgression of chromosomal segments from wild relatives such as Aegilops tauschii has been shown to introduce novel haplotypes that confer resistance to various diseases (Zhou et al., 2021). Additionally, the use of synthetic hexaploid wheats (SHWs) has been effective in incorporating disease resistance traits into bread wheat, as demonstrated by the successful development of varieties with improved resistance profiles (Hao et al., 2019). Exotic germplasm has also been utilized to improve wheat's tolerance to abiotic stresses. For example, recombinant lines of durum wheat with Thinopyrum ponticum segments have shown remarkable stability and improved performance under heat and water-deficit conditions (Giovenali et al., 2019). Similarly, synthetic-derived wheats have been identified with genomic regions associated with drought adaptability, enhancing their productivity under water-limited conditions (Afzal etal., 2019). The introgression of exotic germplasm has led to significant yield improvements and enhanced quality traits in wheat. The use of synthetic hexaploid wheat in breeding programs has resulted in varieties with higher yield potential compared to those developed through conventional breeding methods (Hao et al., 2019). Moreover, the introgression of wild-relative genes has contributed to the adaptive diversity of modern bread wheat, enhancing both yield and quality traits (He et al., 2019). 4.2 Breeding strategies Introgression breeding involves the transfer of specific traits from exotic germplasm into elite cultivars. This strategy has been successfully employed to introduce beneficial traits such as disease resistance, abiotic stress tolerance, and yield improvement. For instance, the introgression of Aegilops tauschii genetic variations into wheat has enriched the germplasm pool and facilitated the development of high-yielding varieties (Zhou et al., 2021). Additionally, targeted introgression of chromosome segments from exotic germplasm has been shown to improve yield and other agronomic traits in soybean, suggesting its potential applicability in wheat breeding (Ru and Bernardo, 2019). Pre-breeding and advanced backcrossing are essential strategies for incorporating exotic germplasm into wheat breeding programs. These methods involve the initial crossing of exotic germplasm with elite cultivars, followed by multiple backcrosses to recover the desirable traits while minimizing linkage drag. The use of double top-cross (DTC) and two-phase selection procedures has been demonstrated to be effective in developing high-yielding wheat varieties with introgressed traits from synthetic hexaploid wheat (Hao et al., 2019). Moreover, advanced backcrossing has been employed to introduce and pyramid specific chromosome segments from exotic germplasm into elite cultivars, achieving significant genetic gains (Ru and Bernardo, 2019).
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