Cotton Genomics and Genetics 2024, Vol.15, No.2, 93-102 http://cropscipublisher.com/index.php/cgg 94 potential applications of introgression in cotton breeding programs. By synthesizing findings from recent studies, this study will provide a comprehensive understanding of how interspecific introgression drives adaptation and enhances the genetic potential of Gossypiumspecies. 2GossypiumGenus: Diversity and Evolution 2.1 Taxonomy and classification The Gossypiumgenus, commonly known as cotton, comprises approximately 50 species, including both diploid and tetraploid species. The primary cultivated species are Gossypium hirsutumand Gossypium barbadense, both of which are tetraploid and originated in the Americas. These species are classified based on their genomic constitution, with G. hirsutum and G. barbadense sharing the AD genome, a result of an ancient hybridization event between an A-genome diploid and a D-genome diploid species (Nie et al, 2020; Fang et al., 2021; Wang et al., 2022). 2.2 Geographic distribution and habitat variability Gossypium species are distributed globally, with a significant presence in tropical and subtropical regions. G. hirsutumis widely cultivated due to its high yield, while G. barbadense is valued for its superior fiber quality. The geographic distribution of these species has been influenced by human cultivation practices, leading to their presence in diverse habitats ranging from arid to semi-arid regions. The adaptability of these species to various environmental conditions is partly due to interspecific introgression, which has introduced beneficial traits from one species to another, enhancing their ability to thrive in different habitats (Nie et al, 2020; Fang et al., 2021; Wang et al., 2022). 2.3 Evolutionary history and phylogeny The evolutionary history of the genus Gossypiumis characterized by hybridization and polyploidization events. Tetraploid species, including G. hirsutumand G. barbadense, originated from a hybridization event between an A-genome species from Africa or Asia and a D-genome species from the Americas. This event led to the formation of the AD genome, which has been crucial for the diversification and adaptability of these species. Introgression between species has played a key role in the evolutionary dynamics of Gossypium, promoting genetic diversity and the development of agriculturally important traits. Studies have shown that introgression fromG. hirsutumto G. barbadense significantly influenced the latter's genetic structure and phenotypic traits, enhancing its adaptation to various environments and improving fiber quality (Zhang et al., 2016; Nie et al., 2020; Fang et al., 2021; Wang et al., 2022). Interspecific introgression events between G. barbadense and G. hirsutum have primarily driven population differentiation and agronomic trait variation (Figure 1). These introgression events have significantly increased the genetic diversity and degree of differentiation in G. barbadense. Figure 1 shows the geographical distribution of 93 ex-situ samples collected in 1967 in Morelos, Mexico, and 13 in-situ samples re-collected in 2017. These samples represent maize landraces from different municipalities, providing detailed geographical references and sample race information. The different colors and shapes of the points indicate the status of the samples in 2017 and the races they represent, such as Ancho, Chalqueño, Cónico, Pepitilla, and Elotes Cónicos. Through these geographical distributions and sample descriptions, the study reveals the genetic diversity and selective pressures in different regions. This figure illustrates that landraces exhibit significant genetic variation across different geographical areas, highlighting the importance of in-situ and ex-situ conservation strategies in maintaining and utilizing maize genetic diversity. The Gossypium genus exhibits remarkable diversity and evolutionary complexity, driven by hybridization, polyploidization, and interspecific introgression. These processes have not only shaped the taxonomy and classification of the genus but also enabled its widespread geographic distribution and adaptation to diverse habitats. The evolutionary history and phylogeny of Gossypiumhighlight the importance of genetic exchange in the development of traits that are critical for the survival and cultivation of these economically important species.
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