Legume Genomics and Genetics 2024, Vol.15, No.3, 93-104 http://cropscipublisher.com/index.php/lgg 95 2.2 Fossil records and molecular evidence of early legume evolution Fossil records and molecular evidence have been pivotal in tracing the early evolution of legumes. The earliest evidence of the legume family dates back to the Late Campanian period, with fossil legume fruits discovered in northern Mexico, suggesting that Mexico could be a center of Fabaceae radiation (Centeno-González et al., 2021). Additionally, the Cretaceous-Paleogene (K-Pg) boundary mass extinction event played a crucial role in the evolution of plant diversity, including legumes. Multiple whole genome duplication (WGD) events around this period are hypothesized to have contributed to the survival and diversification of legume lineages (Koenen et al., 2020). These WGDs, along with subsequent polyploidization events, have been confirmed through phylogenomic analyses, further elucidating the complex evolutionary history of legumes (Cannon et al., 2015; Zhao et al., 2021). 2.3 Geographic origins and diversification of wild legumes The geographic origins and diversification of wild legumes are deeply rooted in their evolutionary history. The tribe Fabeae, which includes ancient and important crops like lentil, pea, and broad bean, is believed to have originated in the East Mediterranean region during the Miocene epoch (23~16 million years ago) (Schaefer et al., 2012). From there, legumes spread across Eurasia, into tropical Africa, and the Americas through multiple long-distance dispersal events. This widespread distribution is supported by the high representation of legumes in ex situ germplasm collections, with over 1 000 000 accessions worldwide (Smýkal et al., 2015). The diversification of legumes is also marked by rapid evolutionary changes in their chloroplast genomes, which have undergone significant genomic diversification, contributing to the adaptability and success of legume species in various environments (Guo et al., 2007). In summary, the origins and early evolution of legumes are characterized by a complex interplay of phylogenetic relationships, fossil records, and molecular evidence. The simultaneous origin of subfamilies, the impact of the K-Pg mass extinction event, and the geographic diversification from the East Mediterranean region have all played crucial roles in shaping the evolutionary trajectory of the Fabaceae family. 3 Domestication of Legumes 3.1 Transition from wild ancestors to domesticated crops The domestication of legumes, like many other crops, involved a series of evolutionary and selective processes that transformed wild species into the cultivated varieties we rely on today. This transition was marked by significant genetic and phenotypic changes driven by human selection. For instance, the common bean (Phaseolus vulgaris) underwent a transformation that included the selection of traits such as reduced pod dehiscence, which was crucial for cultivation in arid regions (Parker et al., 2019). Similarly, the domestication of grain legumes like soybean (Glycine max) involved the selection of traits that facilitated adaptation to different latitudinal zones, such as changes in flowering time (Lu et al., 2020). The process of legume domestication has been extensively studied through genomic and archaeobotanical analyses, revealing the complex interplay between human selection and natural genetic variation (Fuller, 2007; Rendón-Anaya et al., 2017). 3.2 Key traits selected during domestication Several key traits were selected during the domestication of legumes to enhance their suitability for agriculture: Seed Size: Increased seed size was a common trait selected in many domesticated legumes. This trait was particularly important for improving yield and ease of harvest. For example, archaeobotanical evidence suggests that seed size in legumes like mung beans (Vigna radiata) and urd beans (Vigna mungo) increased significantly during the early stages of domestication (Fuller, 2007). Pod Dehiscence: The reduction of pod dehiscence, or the tendency of pods to shatter and disperse seeds, was a critical trait selected in many legumes. This trait was essential for reducing seed loss during harvest. Studies on common bean and pea (Pisum sativum) have shown that multiple genetic loci control pod dehiscence, and selection for reduced dehiscence was a key step in their domestication (Hradilová et al., 2017; Parker et al., 2019; Parker et al., 2021).
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