Triticeae Genomics and Genetics, 2024, Vol.15, No.4, 173-184 http://cropscipublisher.com/index.php/tgg 175 number, along with a reduction in non-reproductive biomass, were crucial adaptations that improved the productivity of these crops (Preece et al., 2016). Genetic studies have revealed that domesticated wheat populations have undergone substantial introgression from wild populations, contributing to their genetic diversity and adaptive success. Whole-genome sequencing of bread wheat has shown that introgression from wild populations accounts for a significant portion of the bread wheat genome, enhancing its ability to adapt to diverse environments. This genetic diversity, combined with convergent adaptation to human selection, has played a critical role in the global spread and success of wheat as a major crop (Zhou et al., 2020). 3 Mechanisms of Spread and Expansion 3.1 Early agricultural practices The domestication of Triticeae crops, including wheat and barley, began in Southwest Asia around 10 000 to 11 000 years ago. This marked the transition from hunter-gatherer societies to agrarian communities, fundamentally altering human lifestyles. Early agricultural practices involved the cultivation of wild ancestors of these crops, which led to the development of Neolithic cultures characterized by food production, permanent settlements, and specialized tools. The spread of these agricultural practices from the Near East into Europe and other regions was facilitated by the adaptability of these crops to different environmental conditions. For instance, barley's genetic diversity allowed it to thrive in various climates, contributing to its widespread cultivation (Zhou et al., 2020). The processing of wild cereal grains also played a crucial role in early agricultural practices. Evidence from the Upper Palaeolithic site of Ohalo II in Israel indicates that humans were processing barley and possibly wheat as early as 12 000 years ago. This involved grinding the hard, fibrous seeds into flour and baking it into dough, which made the grains more digestible and nutritious (Piperno et al., 2004). Such practices not only improved the utility of these crops but also likely encouraged their cultivation and spread as staple foods in early agrarian societies. 3.2 Trade and migration routes The expansion of Triticeae crops was significantly influenced by ancient trade and migration routes. For example, the spread of wheat into China is believed to have occurred through three primary routes: across the Eurasian Steppe, by sea from India to the east coast of Eurasia, and along the Hexi Corridor, part of the Silk Road in western China (Jones et al., 2016). These routes facilitated the exchange of agricultural knowledge and practices, as well as the movement of seeds and crops, thereby promoting the spread of Triticeae crops across vast regions. In Europe, the spread of Neolithic agriculture, including the cultivation of barley, was influenced by adaptive genetic traits that allowed these crops to thrive in diverse climates. The photoperiod response gene PPD-H1 in barley, for instance, enabled the crop to flower in response to increasing day lengths in spring, which was crucial for its successful cultivation in northern and higher altitude regions (Jones et al., 2012). This genetic adaptation, along with the movement of early farming communities, contributed to the widespread distribution of Triticeae crops across Europe. 3.3 Role of ancient civilizations Ancient civilizations played a pivotal role in the spread and adaptation of Triticeae crops. The Fertile Crescent, often referred to as the cradle of agriculture, was the initial center of domestication for wheat and barley. From this region, these crops spread to other parts of the world, facilitated by the agricultural practices and trade networks established by ancient civilizations (Levy and Feldman, 2022). The genetic diversity of these crops, enhanced by introgression from wild populations, allowed them to adapt to various environmental conditions, further aiding their global distribution (Zhou et al., 2020). The role of ancient civilizations is also evident in the genetic adaptations observed in Triticeae crops. For instance, the selection of specific genetic variants, such as the barley homolog of Antirrhinum CENTRORADIALIS (HvCEN), contributed to the successful adaptation of barley to new environments encountered as early farming
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