Triticeae Genomics and Genetics, 2024, Vol.15, No.1, 56-65 http://cropscipublisher.com/index.php/tgg 63 Despite the reduction in nucleotide diversity, domesticated barley has adapted to a wide range of agricultural environments. Exome sequencing of geographically diverse barley landraces and wild relatives revealed that patterns of genetic variation are strongly shaped by geography, with significant correlations between genetic traits and environmental variables such as temperature and dryness (Russell et al., 2016). This adaptation is facilitated by the extensive sequence variation in flowering-associated genes, which exhibit strong geographical structuring and contribute to regional success. 5 The Significance and Challenges of Domestication on Nucleotide Diversity in Barley Domestication has played a crucial role in shaping the genetic makeup of barley, one of the oldest cultivated crops. The process of domestication, which began around 10 500 years ago in the Fertile Crescent, involved selecting traits favorable for agriculture, such as increased seed size and non-shattering spikes (Kilian et al., 2006). This selection process, while beneficial for crop yield and ease of harvest, has led to a significant reduction in nucleotide diversity. For instance, domesticated barley shows a marked decrease in haplotype number and nucleotide diversity compared to its wild progenitors (Kilian et al., 2006). This reduction in genetic diversity poses challenges for crop resilience and adaptability, as it limits the genetic pool available for breeding programs aimed at improving disease resistance and environmental stress tolerance (Smýkal et al., 2018). 5.1 Inspiration for crop breeding and genetic improvement The study of domestication genes in barley provides valuable insights for crop breeding and genetic improvement. Key domestication traits, such as the six-rowed spike, have been linked to specific genetic changes, offering a framework for understanding and manipulating these traits in modern breeding programs (Ramsay et al., 2011). The identification of genes like SIX-ROWED SPIKE 1 (VRS1) and its modifiers, such as INTERMEDIUM-C (INT-C), which is an ortholog of the maize domestication gene TEOSINTE BRANCHED 1, highlights the potential for using genetic knowledge to enhance barley yields and adaptability (Ramsay et al., 2011). Moreover, the discovery of photoperiod-response genes shared between barley and rice suggests that similar genetic networks can be targeted across different crops to improve agricultural productivity. 5.2 Impact on diversity and sustainability of agricultural ecosystems The reduction in nucleotide diversity due to domestication has significant implications for the sustainability of agricultural ecosystems. Lower genetic diversity in domesticated barley can lead to increased vulnerability to pests, diseases, and changing environmental conditions (Smýkal et al., 2018). This genetic bottleneck effect, observed in both barley and other crops like wheat, underscores the importance of maintaining and utilizing wild relatives and landraces in breeding programs to reintroduce lost genetic variation (Russell et al., 2011). The ongoing adaptation of landrace barley through hybridization with wild types, as evidenced by secondary contact and chromosome-level differences in diversity, suggests that maintaining a diverse genetic pool is crucial for the long-term sustainability of barley cultivation (Russell et al., 2011). 5.3 Challenges and future research directions One of the primary challenges in barley domestication research is understanding the complex interplay between selection, genetic drift, and gene flow. The significant reduction in genetic diversity observed in domesticated barley necessitates a comprehensive approach to identify and preserve beneficial alleles from wild populations (Kilian et al., 2006, Smýkal et al., 2018). Future research should focus on leveraging advanced molecular technologies, such as genome sequencing and SNP analysis, to map the genetic architecture of domestication traits and identify regions of the genome under selection (Russell et al., 2011, Smýkal et al., 2018). Additionally, exploring the demographic histories of barley domestication through population-level molecular analyses can provide insights into the origins and spread of domesticated barley, informing strategies for genetic conservation and improvement (Smýkal et al., 2018). Addressing these challenges will be critical for enhancing the resilience and productivity of barley in the face of global agricultural demands. 6 Concluding Remarks This study discusses the impact of domestication on the nucleotide diversity and genetic structure of barley, revealing the loss of genetic diversity in barley during domestication, especially the loss of alleles and the
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