Maize Genomics and Genetics 2024, Vol.15 http://cropscipublisher.com/index.php/mgg © 2024 CropSci Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved.
Maize Genomics and Genetics 2024, Vol.15 http://cropscipublisher.com/index.php/mgg © 2024 CropSci Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. CropSci Publisher is an international Open Access publishing specializing in maize genome, trait-controlling, maize gene expression and regulation at the publishing platform that is operated by Sophia Publishing Group (SPG), founded in British Columbia of Canada Publisher Cropsci Publisher Editedby Editorial Team of Maize Genomics and Genetics Email: edit@mgg.cropscipublisher.com Website: http://cropscipublisher.com/index.php/mgg Address: 11388 Stevenston Hwy, PO Box 96016, Richmond, V7A 5J5, British Columbia Canada Maize Genomics and Genetics (ISSN 1925-1971) is an open access, peer reviewed journal published online by CropSci Publisher. The journal is committed to publishing basic theories, novel techniques, and new advances within all aspects of maize research, especially focusing on genetics and genomics. Papers regarding classical genetics analysis, structural and functional analysis of maize genome, trait-controlling, maize gene expression and regulation, transgenic maize, as well as maize varietal improvement, are especially welcomed. All the articles published in Maize Genomics and Genetics are Open Access, and are distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. CropSci Publisher uses CrossCheck service to identify academic plagiarism through the world’s leading plagiarism prevention tool, iParadigms, and to protect the original authors’ copyrights.
Maize Genomics and Genetics (online), 2024, Vol. 15, No.3 ISSN 1925-1971 http://cropscipublisher.com/index.php/mgg © 2024 CropSci Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. Latest Content The Columbian Exchange: Maize's Global Journey and Ecological Impact Jiansheng Li Maize Genomics and Genetics, 2024, Vol. 15, No. 3, 102-110 Genomics-Assisted Breeding in Maize: Techniques and Outcomes Lan Zhou, Long Jiang Maize Genomics and Genetics, 2024, Vol. 15, No. 3, 111-122 Transposable Elements in Zea: Their Role in Genetic Diversity and Evolution Shaomin Yang Maize Genomics and Genetics, 2024, Vol. 15, No. 3, 123-135 Utilizing Genetic Diversity for Maize Improvement: Strategies and Success Stories Bin Chen, Junfeng Hou, Yunfei Cai, Guiyue Wang, Renxiang Cai, Fucheng Zhao Maize Genomics and Genetics, 2024, Vol. 15, No. 3, 136-146 Transposons in Zea Genomics: Their Impact on Genetic Architecture ZhenLi Maize Genomics and Genetics, 2024, Vol. 15, No. 3, 147-159
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 102 Feature Review Open Access The Columbian Exchange: Maize’s Global Journey and Ecological Impact Jiansheng Li Sanya Institute of China Agricultural University, Sanya, 572025, Hainan, China Corresponding email: lijiansheng@cau.edu.cn Maize Genomics and Genetics, 2024, Vol.15, No.3 doi: 10.5376/mgg.2024.15.0011 Received: 18 Mar., 2024 Accepted: 22 Apr., 2024 Published: 05 May, 2024 Copyright © 2024 Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li J.S., 2024, The Columbian exchange: maize’s Global journey and ecological impact, Maize Genomics and Genetics, 15(3): 102-110 (doi: 10.5376/mgg.2024.15.0011) Abstract This study examines the global journey of maize (Zea mays) and its profound ecological impact through the lens of the Columbian Exchange. Maize, originally domesticated in Mesoamerica, was introduced to Europe, Africa, and Asia, where it adapted to various climatic and ecological conditions. The introduction of maize marked a significant event in agricultural history, leading to a profound impact on local ecosystems and cultures. The ecological impact of maize introduction includes changes in soil fertility, agricultural land use, and biodiversity. Meanwhile, the introduction of maize influenced demographic shifts and socio-economic dynamics, underscoring its importance as a global crop. This study highlights maize’s journey through the Columbian Exchange and its ecological and cultural significance, offering a comprehensive understanding of how a single crop can influence global history and ecosystems. Keywords Maize (Zeamays); Columbian exchange; Introduction; Global journey; Ecological impact 1 Introduction The Columbian Exchange, initiated by Christopher Columbus’s voyages to the New World, represents a pivotal moment in global history, characterized by the extensive transfer of plants, animals, culture, human populations, technology, and ideas between the Americas, West Africa, and the Old World. This exchange had profound and lasting impacts on the global ecosystem and human societies. One of the most significant aspects of this exchange was the introduction of New World crops, such as maize (Zeamays), to various parts of the world, which played a crucial role in shaping agricultural practices and societal structures (McCook et al., 2011; Cherniwchan et al., 2017; Galesi, 2021). Before the arrival of Europeans, maize was a staple crop in many Pre-Columbian societies across the Americas. It was not only a primary food source but also held cultural and economic significance. The genetic diversity and population structure of native maize populations in Latin America and the Caribbean reflect the extensive cultivation and selective breeding practices that occurred over millennia (Bedoya et al., 2017). The introduction of maize to other continents, such as Europe and Africa, during the Columbian Exchange, further underscores its importance and adaptability as a crop (Cherniwchan et al., 2017; Galesi, 2021). By examining historical records, genetic studies, and ecological data, this study aims to trace the diffusion of maize from the Americas to Europe, Africa, and other regions, analyze the genetic diversity and adaptation of maize in different ecological contexts, assess the socio-economic and ecological impacts of maize introduction in various regions, and highlight the role of maize in shaping agricultural practices and societal changes during and after the Columbian Exchange. By achieving these objectives, this study will contribute to a deeper understanding of the complex interactions between human societies and their environments, facilitated by the movement of a single, yet highly influential, crop. 2 Historical Overview of Maize's Domestication and Early Spread 2.1 Origins of maize domestication in Mesoamerica Maize, or Zea mays, is believed to have been domesticated in the region of Mesoamerica, specifically in the area that is now southern Mexico (Figure 1). Genetic studies have shown that maize was derived from a wild grass known as teosinte. The domestication process, which began around 9 000 years ago, involved selective breeding
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 103 by indigenous peoples to enhance desirable traits such as kernel size and ease of harvest. This early genetic manipulation laid the foundation for maize to become a staple crop in various cultures across the Americas (Bedoya et al., 2017). Figure 1 Suggested maize migration routes from its center of origin in Mesoamerica based on archeological evidence, historic and anthropological studies, and genetic relationships (Adopted from Bedoya et al., 2017) Image caption: Red arrows indicate early maize dispersal from its origin center in Mesoamerica towards northern Mexico and Central America; dashed orange arrows represents the likely Pacific Ocean routes via maritime technologies in Pre-Columbian times; green arrows show maize migrations from the mainland to the Caribbean; light green arrows show routes followed by the Caribbean communities along the eastern coast and rivers; blue arrows correspond to movements in the Andean region in different directions. Ovals correspond to important zones of maize germplasm interchange (Adopted from Bedoya et al., 2017) 2.2 Early cultivation and uses in indigenous cultures Following its domestication, maize quickly became a central component of the diet and culture of many indigenous groups in Mesoamerica. It was not only a primary food source but also held significant cultural and religious importance. The cultivation techniques and uses of maize varied among different indigenous cultures, reflecting the adaptability and versatility of the crop. For instance, maize was used in various forms such as tortillas, tamales, and beverages, and it played a crucial role in agricultural systems that included companion planting with beans and squash (Bedoya et al., 2017). 2.3 Initial spread of maize within the Americas The spread of maize from its point of origin in Mesoamerica to other parts of the Americas was facilitated by both human migration and trade networks. Genetic evidence suggests that maize reached the Andean region relatively early, where it was integrated into local agricultural practices with minimal genetic mixing from other regions (Bedoya et al., 2017). Additionally, the movement of maize into the Caribbean is thought to have been influenced by two separate human migration events, which contributed to the genetic diversity observed in Caribbean maize populations. The pre-Columbian exchange of maize germplasm between North and South America underscores the crop's importance and the interconnectedness of indigenous cultures long before European contact. By the time Europeans arrived in the Americas, maize had already become a well-established and vital crop across a vast geographical area, setting the stage for its subsequent introduction to Europe and other parts of the world during the Columbian Exchange (Galesi, 2021).
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 104 3 Maize’s Journey through the Columbian Exchange 3.1 Introduction of maize to Europe The introduction of maize (Zea mays) to Europe is a pivotal chapter in the story of the Columbian Exchange. When Christopher Columbus returned from his first voyage to the New World in 1493, he brought with him a variety of unfamiliar crops, including maize. This crop, native to the Americas, quickly caught the attention of European farmers and botanists due to its high yield potential and versatility. Initially considered a curiosity, maize soon proved to be a valuable addition to the European agricultural repertoire (Revilla et al., 2022). In Southern Europe, particularly Spain and Portugal, maize was rapidly adopted due to favorable climatic conditions similar to those in its native regions. By the early 16th century, maize cultivation spread throughout the Mediterranean basin. The crop's ability to thrive in diverse environments and its relatively short growing season made it an attractive option for farmers. Additionally, maize's role as a staple food provided a buffer against famines caused by the failure of traditional European crops, such as wheat and barley. Over time, maize became a staple in the diets of various European populations, particularly in rural areas where it was often ground into flour for bread and porridge (Ranum et al., 2014). 3.2 Spread to Africa and Asia The dissemination of maize to Africa and Asia marked another significant phase in its global journey. Portuguese traders played a crucial role in introducing maize to Africa, where it quickly became a vital crop due to its adaptability to various climatic conditions and its high nutritional value. Maize found fertile ground in the African continent, particularly in regions with poor soils and erratic rainfall, where traditional crops often failed (Galani et al., 2022). In sub-Saharan Africa, maize became a staple food, integrated into local agricultural systems and dietary practices. Its versatility allowed it to be used in various forms, from fresh cobs to dried kernels and flour. The crop's introduction also had socio-economic impacts, providing a reliable food source and contributing to food security. However, maize's dominance also led to changes in traditional farming practices and dietary habits, sometimes at the expense of indigenous crops. The spread of maize to Asia followed a similar trajectory. Portuguese and Spanish traders introduced the crop to the Indian subcontinent, China, and Southeast Asia in the 16th and 17th centuries. In China, maize was initially grown as a supplementary crop but soon became integral to the agricultural landscape, especially in mountainous and arid regions where rice and wheat cultivation was challenging. The crop's high yield and resilience to diverse environmental conditions made it an essential food source for the growing population. In India, maize complemented traditional crops like millet and sorghum, contributing to the diversification of agricultural production and food security (Murdia et al., 2016). 3.3 Factors influencing maize's global dissemination Several factors facilitated the global dissemination of maize during and after the Columbian Exchange. One of the primary drivers was the adaptability of maize to a wide range of climatic and soil conditions. This adaptability allowed maize to thrive in diverse environments, from the temperate climates of Europe to the tropical and subtropical regions of Africa and Asia (Gong et al., 2015). Trade and exploration were also critical in spreading maize. European explorers and traders, particularly the Portuguese and Spanish, were instrumental in introducing maize to new regions. Their extensive trade networks facilitated the exchange of agricultural products, including maize, between the Old and New Worlds. The role of colonial powers in establishing agricultural practices in their colonies further accelerated the spread of maize (Ranum et al., 2014). Cultural exchange played a significant role in the acceptance and integration of maize into local diets and agricultural systems. In many regions, maize was incorporated into existing food traditions, often replacing or supplementing traditional staples. Its versatility in culinary uses—from fresh cobs to various processed forms-enhanced its appeal and adoption (Palacios-Rojas et al., 2020).
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 105 Additionally, the nutritional benefits of maize contributed to its widespread adoption. As a high-calorie crop with essential vitamins and minerals, maize became a crucial food source in many parts of the world, particularly in regions prone to food insecurity. Its role in preventing famine and supporting population growth underscored its importance in global agricultural systems (Nuss and Tanumihardjo, 2010). 4 Agronomic and Economic Impacts 4.1 Changes in agricultural practices The introduction of maize to various regions during the Columbian Exchange significantly altered agricultural practices. In precolonial Africa, maize became a staple crop, leading to changes in land use and farming techniques. The crop's adaptability to different climates and soils allowed it to be cultivated in areas where traditional African crops were less successful, thereby increasing agricultural productivity (Cherniwchan et al., 2017). Additionally, the introduction of maize necessitated new farming tools and methods, which were adopted to optimize maize cultivation and harvest. 4.2 Economic significance in various regions Maize's economic impact varied across different regions. In Africa, the introduction of maize had profound demographic and economic consequences. The crop's high yield and nutritional value contributed to population growth, which in turn increased the supply of labor and slaves during the Trans-Atlantic slave trade (Cherniwchan et al., 2017). However, the economic benefits were not uniformly positive; while maize supported population growth, it did not significantly stimulate broader economic development or reduce conflict (Cherniwchan et al., 2017). In the Old World, the introduction of maize provided a new food source that complemented existing agricultural systems, thereby enhancing food security and supporting economic stability (Nunn and Qian, 2010). 4.3 Development of maize-based industries The global journey of maize also spurred the development of maize-based industries. In regions where maize became a staple, various industries emerged to process and utilize the crop. For instance, the production of maize flour and other maize-derived products became significant economic activities. These industries not only provided employment but also contributed to the economic diversification of the regions involved. The widespread cultivation and processing of maize led to the establishment of trade networks that facilitated the exchange of maize products, further integrating maize into the global economy (Nunn and Qian, 2010; Cherniwchan et al., 2017). It can be seen that the introduction of maize during the Columbian Exchange had far-reaching agronomic and economic impacts. It transformed agricultural practices, influenced demographic and economic dynamics, and led to the development of maize-based industries, thereby playing a crucial role in shaping the agricultural and economic landscapes of the regions it reached. 5 Ecological and Environmental Impacts 5.1 Impact on soil fertility and agricultural land The introduction of maize during the Columbian Exchange had significant implications for soil fertility and agricultural land use across various regions. Maize, a staple crop from the New World, was integrated into the agricultural systems of the Old World, leading to both positive and negative environmental outcomes. One of the primary impacts of maize cultivation was on soil fertility. Maize is known to be a nutrient-demanding crop, requiring substantial amounts of nitrogen, phosphorus, and potassium for optimal growth. This high nutrient demand often led to soil depletion in areas where maize was grown intensively without adequate crop rotation or soil management practices. The continuous cultivation of maize without replenishing soil nutrients resulted in the degradation of soil quality over time, making the land less productive for future agricultural use (Nunn et al., 2010; Cherniwchan et al., 2017). In precolonial Africa, the introduction of maize had a profound effect on agricultural land use. The suitability of African land for growing maize and and its relatively high yield compared to traditional African staples like millet
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 106 and sorghum made it an attractive option for farmers. This shift in crop preference led to changes in land use patterns, with more land being allocated to maize cultivation (Figure 2). However, the increased focus on maize also meant that traditional practices of crop rotation and fallowing were often neglected, further exacerbating soil fertility issues (Cherniwchan et al., 2017). Moreover, in some regions, the increased productivity associated with maize cultivation supported higher population densities. This demographic shift placed additional pressure on agricultural land, as more food was needed to sustain the growing population. Consequently, the intensification of maize farming often led to the overexploitation of land resources, contributing to soil erosion and loss of arable land (Cherniwchan et al., 2017). Figure 2 The suitability of land for cultivating maize in Africa (Adopted from Cherniwchan et al., 2017) 5.2 Effects on biodiversity and local ecosystems One significant impact of maize introduction was the alteration of local ecosystems in Europe. The genetic uniformity of the maize initially brought to Europe meant that it had specific environmental requirements and traits that influenced how it integrated into existing agricultural systems. This genetic bottleneck could have led to reduced biodiversity as local farmers might have focused on cultivating this new, high-yield crop at the expense of traditional varieties (Galesi, 2021). In Africa, the introduction of maize had a different set of ecological consequences. The crop's adaptability to various climates allowed it to spread rapidly, often replacing indigenous crops. This shift not only altered the agricultural landscape but also had broader ecological implications. The increased cultivation of maize could have led to changes in soil composition and local flora, potentially reducing the diversity of plant species in the region (Cherniwchan et al., 2017). The broader environmental impacts of maize introduction also included changes in land use patterns. In many regions, the high productivity of maize encouraged the expansion of agricultural land, often at the expense of natural habitats. This expansion could have led to deforestation and habitat loss, further impacting local biodiversity. The shift in land use patterns was particularly evident in Europe, where maize cultivation became a significant part of the agricultural economy (Nunn and Qian, 2010; Galesi, 2021).
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 107 Moreover, the introduction of maize influenced local ecosystems by altering the food web. In regions where maize became a staple crop, it affected the diet of both humans and livestock. This dietary shift could have had cascading effects on local wildlife, as changes in livestock feeding practices might have influenced the availability of certain plant species and the overall structure of the ecosystem (Nunn and Qian, 2010). The ecological impact of maize was also evident in its role in the Columbian Exchange's broader environmental changes. The movement of maize across continents was part of a larger pattern of biotic exchange that included the transfer of other crops, animals, and even diseases. This complex web of interactions had far-reaching consequences for ecosystems around the world, contributing to both the homogenization and diversification of global biodiversity (Nunn and Qian, 2010). 6 Cultural and Societal Impacts 6.1 Maize in culinary traditions The introduction of maize to various parts of the world significantly transformed culinary traditions. In Europe, maize became a staple ingredient, integrating into the daily diets and cultural spaces of early modern Europeans. This transformation is evident in the way maize was naturalized into European cuisine, alongside other New World ingredients such as tomatoes, chiles, and chocolate. The adoption of maize in European culinary practices highlights the broader impact of the Columbian Exchange on global eating habits, showcasing how new foods were incorporated into existing culinary traditions and became familiar staples over time (Galesi, 2021). 6.2 Societal changes and population growth The introduction of maize had profound societal impacts, particularly in terms of population growth and demographic changes. In precolonial Africa, the arrival of maize contributed to increased population density and had significant implications for the Trans-Atlantic slave trade. The robust empirical evidence suggests that maize's introduction did not stimulate economic development but rather increased the supply of slaves from Africa during the Trans-Atlantic slave trade (Cherniwchan et al., 2017). Additionally, the genetic diversity and population structure of native maize populations in Latin America and the Caribbean reflect the historical migration and exchange of maize, which played a crucial role in the development and expansion of pre-Columbian cultures and the demographic shifts following European colonization (Bedoya et al., 2017). 6.3 Symbolism and cultural significance in different societies Maize holds deep symbolic and cultural significance in various societies. In Europe, the unique characteristics of maize seeds influenced how the crop fit into European ecosystems and cultures, reflecting its broader cultural impact (Galesi, 2021). The Columbian Exchange facilitated the transfer of not only crops but also cultural symbols and practices, leading to a rich interplay between biological and social forces. The cultural significance of maize is also evident in its role in the adaptive introgression in human populations, where the exchange of genetic material between populations led to novel human genomes shaped by rapid adaptive evolution (Jordan, 2016). This underscores the importance of maize not only as a food source but also as a cultural and symbolic element that influenced human societies in diverse ways. 7 Challenges and Controversies 7.1 Genetic modification and biotechnology The genetic diversity and population structure of native maize populations in Latin America and the Caribbean have been extensively studied, revealing significant genetic variation among different landraces. This diversity is crucial for the development of genetically modified (GM) maize, as it provides a broad genetic base for biotechnological advancements. However, the introduction of GM maize has sparked controversy due to potential risks to native maize varieties and the environment. The genetic characterization of 194 native maize populations using SSR markers highlights the importance of preserving genetic diversity to ensure the sustainability of maize cultivation in the face of biotechnological interventions (Bedoya et al., 2017).
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 108 7.2 Sustainability and environmental concerns The diffusion of maize across Europe following the Columbian Exchange has raised several sustainability and environmental concerns. The introduction of maize into European ecosystems, which were previously unfamiliar with the crop, led to significant ecological changes. The unique characteristics of the maize seeds transported to Europe, originating from a narrow gene pool, influenced how maize integrated into European agricultural systems and ecosystems. This integration posed challenges related to soil health, water usage, and biodiversity. Understanding the ecological impact of maize's introduction into new environments is essential for developing sustainable agricultural practices that minimize negative environmental consequences (Galesi, 2021). 7.3 Food security and ethical considerations The role of maize in global food security is a critical issue, particularly in regions heavily reliant on this staple crop. The ethical considerations surrounding maize cultivation and distribution are multifaceted. On one hand, maize's adaptability and high yield potential make it a valuable crop for addressing food security challenges. On the other hand, the historical and ongoing displacement of native maize varieties by commercial hybrids and GM maize raises ethical concerns about the preservation of cultural heritage and traditional agricultural practices. The genetic diversity of native maize populations, as documented in Latin America and the Caribbean, underscores the need to balance modern agricultural practices with the preservation of traditional knowledge and biodiversity (Bedoya et al., 2017; Galesi, 2021). The global journey of maize, initiated by the Columbian Exchange, has led to significant challenges and controversies in the realms of genetic modification, sustainability, and food security. Addressing these issues requires a nuanced understanding of maize's genetic diversity, ecological impact, and ethical implications to ensure a sustainable and equitable future for maize cultivation worldwide. 8 Future Prospects and Research Directions 8.1 Innovations in maize cultivation and breeding Advancements in maize cultivation and breeding are poised to revolutionize agricultural practices. Modern techniques such as precision agriculture, which employs data analytics, GPS, and IoT technologies, allow for optimized planting, irrigation, and fertilization. This results in enhanced crop yields and reduced environmental impact (Thudi et al., 2020). Genomic selection and CRISPR-Cas9 gene editing hold promise for accelerating maize breeding programs. These technologies enable the development of maize varieties with desirable traits such as drought tolerance, pest resistance, and improved nutritional content. The integration of these advanced breeding techniques can significantly contribute to food security and sustainable agriculture (Agarwal et al., 2018; Nerkar et al., 2022). Moreover, the exploration of wild maize relatives and landraces can uncover genetic diversity essential for breeding resilient maize varieties. Collaborative international research initiatives and biobanks are crucial in preserving and utilizing this genetic diversity. 8.2 Maize in bioenergy and industrial applications Maize is increasingly recognized for its potential in bioenergy production and various industrial applications. The development of maize-based biofuels, such as ethanol and biodiesel, offers a renewable energy source that can reduce dependency on fossil fuels and mitigate greenhouse gas emissions (Wang et al., 2022). In addition to biofuels, maize is a valuable feedstock for bioplastics, biochemicals, and other bioproducts. The starch and cellulose components of maize can be converted into biodegradable plastics, reducing plastic pollution and promoting a circular economy. Research into optimizing the conversion processes and enhancing the efficiency of maize-based bioproducts is essential for their widespread adoption (Khulbe et al., 2020). Furthermore, the use of maize in industrial applications extends to pharmaceuticals, textiles, and construction materials. Continued research and innovation in these areas can expand the versatility of maize, making it a cornerstone of sustainable industrial development.
Maize Genomics and Genetics 2024, Vol.15, No.3, 102-110 http://cropscipublisher.com/index.php/mgg 109 8.3 Potential role in addressing global food challenges As the global population continues to grow, maize's role in addressing food security challenges becomes increasingly significant. Maize is a staple crop for many regions, providing essential nutrients and calories. Efforts to enhance maize productivity and nutritional quality can have a profound impact on global food systems. Biofortification, the process of increasing the nutritional value of crops through conventional breeding and biotechnology, is a promising approach to combat malnutrition. Biofortified maize varieties with higher levels of vitamins, minerals, and essential amino acids can improve the dietary quality of populations dependent on maize as a primary food source (Prasanna et al., 2020; Sethi et al., 2023). Additionally, climate change poses a threat to agricultural productivity, and maize's adaptability to diverse environmental conditions makes it a critical crop for future food resilience. Research focused on developing climate-smart maize varieties that can withstand extreme weather events and changing climatic conditions is crucial (Zenda et al., 2021). 9 Concluding Remarks The Columbian Exchange significantly impacted global agriculture, with maize playing a pivotal role in this transformation. The introduction of maize to Europe, as detailed in “Maize on the Move: The Diffusion of a Tropical Cultivar across Europe”, highlights how maize adapted to European ecosystems and cultures, despite originating from a narrow gene pool. In Africa, the introduction of maize during the Columbian Exchange increased population density and the supply of slaves for the Trans-Atlantic slave trade, although it did not significantly affect economic growth or conflict. The genetic diversity and population structure of native maize populations in Latin America and the Caribbean reveal the extensive pre- and post-Columbian exchanges of maize germplasm, underscoring the crop's historical migration and adaptation. Additionally, the neo-Columbian exchanges of the long nineteenth century further expanded the geographical scope of maize's influence, driven by imperial and transnational scientific institutions. Maize’s journey from the New World to various parts of the globe is a testament to its adaptability and significance. In Europe, maize's integration into local ecosystems and cultures was facilitated by its unique genetic traits, which allowed it to thrive in diverse environments. In Africa, maize's introduction had profound demographic and social implications, particularly in relation to the Trans-Atlantic slave trade. The genetic studies of maize populations in Latin America and the Caribbean highlight the crop's complex history of migration and adaptation, influenced by both pre-Columbian and post-Columbian exchanges. The neo-Columbian exchanges further illustrate maize’s role in the ecological globalization of the Greater Caribbean, driven by economic and scientific developments. The historical journey of maize underscores its importance as a global crop and its profound impact on various societies and ecosystems. Future research should continue to explore the genetic diversity and adaptation mechanisms of maize to better understand its resilience and potential in the face of climate change. Additionally, examining the socio-economic impacts of maize in different historical contexts can provide valuable insights into the crop's role in shaping human societies. The neo-Columbian exchanges offer a rich area for further study, particularly in understanding the long-term ecological and agricultural consequences of these historical processes. By building on the findings of these studies, researchers can contribute to the sustainable development and utilization of maize in the future. Acknowledgment The author extends sincere thanks to two anonymous peer reviewers for their feedback on the manuscript. Conflict of Interest Disclosure The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.
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Maize Genomics and Genetics 2024, Vol.15, No.3, 111-122 http://cropscipublisher.com/index.php/mgg 111 Feature Review Open Access Genomics-Assisted Breeding in Maize: Techniques and Outcomes Lan Zhou, Long Jiang College of Agriculture, Jilin Agricultural Science and Technology University, Jilin, 132101, Jilin, China Corresponding author: jlnykjxyjl@163.com Maize Genomics and Genetics, 2024, Vol.15, No.3 doi: 10.5376/mgg.2024.15.0012 Received: 31 Mar., 2024 Accepted: 06 May, 2024 Published: 22 May, 2024 Copyright © 2024 Zhou and Jiang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Zhou L., and Jiang L., 2024, Genomics-assisted breeding in maize: techniques and outcomes, Maize Genomics and Genetics, 15(3): 111-122 (doi: 10.5376/mgg.2024.15.0012) Abstract Genomics-assisted breeding (GAB) has revolutionized maize breeding by integrating advanced genomic techniques to enhance crop improvement. This study reviews the various techniques and outcomes of GAB in maize, focusing on the integration of genomic selection, genome optimization, and marker-assisted selection. Genomic selection leverages genome-wide marker data to predict breeding values, thereby increasing genetic gains with fewer breeding cycles. Genome optimization, incorporating doubled haploid production and computational simulations, aims to design optimized genomes for maximum genetic gain. Marker-assisted selection, facilitated by high-throughput genotyping platforms, provides cost-effective and efficient genotyping solutions. The outcomes of these techniques include the development of disease-resistant, climate-smart, and high-yielding maize cultivars. The integration of these genomic tools has transformed maize breeding from an empirical art to a data-driven science, promising significant advancements in crop productivity and sustainability Keywords Maize; Genomics-assisted breeding; Genomic selection; Genome optimization; Marker-assisted selection 1 Introduction Maize (Zea mays L.) is one of the most significant crops globally, serving as a crucial source of food, feed, and fuel. Its global production has seen a remarkable increase, with current annual production reaching approximately one billion tons (Yan and Tan, 2019). Maize's adaptability to diverse agro-climatic conditions and its high genetic yield potential have earned it the title "Queen of cereals" (Manoj et al., 2019). As a staple crop, maize plays a vital role in food security and the livelihoods of millions of people worldwide, particularly in regions like sub-Saharan Africa and Latin America (EIAR-Bako and Yadesa, 2021). The increasing global population, projected to reach 9 billion by 2050, underscores the need for continued advancements in maize production to meet the growing demand for food (Yan and Tan, 2019). Traditional maize breeding has faced several challenges, including the lengthy time required for developing new varieties and the limitations in achieving desired traits such as disease resistance, drought tolerance, and nutritional quality (EIAR-Bako and Yadesa, 2021). Conventional breeding methods often involve extensive field trials and selection processes, which can be time-consuming and resource-intensive. Additionally, the genetic diversity within maize populations can complicate the breeding process, making it difficult to achieve consistent improvements in yield and other agronomic traits (Lal et al., 2021). The need to address these challenges has driven the exploration of more efficient and precise breeding techniques. Genomics-assisted breeding has emerged as a promising approach to overcome the limitations of traditional breeding methods. This approach leverages advances in genomics technologies, such as genome sequencing, marker-assisted selection (MAS), and genomic prediction, to accelerate the breeding process and enhance the precision of trait selection (Thudi et al., 2020). By utilizing genomic information, researchers can identify and select for specific genes associated with desirable traits, thereby improving the efficiency and effectiveness of breeding programs (Yang and Yan, 2021). Genomics-assisted breeding also enables the exploration of novel genetic variations and the development of crops with enhanced stress tolerance, nutritional quality, and yield potential (Thudi et al., 2020).
Maize Genomics and Genetics 2024, Vol.15, No.3, 111-122 http://cropscipublisher.com/index.php/mgg 112 The purpose of this study is to provide a comprehensive overview of the techniques and outcomes associated with genomics-assisted breeding in maize. By examining the current state of genomics technologies and their applications in maize breeding, this study highlights the potential benefits and challenges of integrating genomics into breeding programs. The expectations of this study include identifying key advancements in genomics-assisted breeding, evaluating the impact of these advancements on maize production, and providing insights into future directions for research and development in this field. Ultimately, this study seeks to contribute to the ongoing efforts to enhance maize breeding and ensure global food security in the face of growing population and climate change challenges. 2 Genomic Technologies in Maize Breeding 2.1 Genotyping-by-sequencing (GBS) Genotyping-by-Sequencing (GBS) is a cost-effective, high-throughput genotyping method that utilizes restriction enzymes to reduce genome complexity, making it suitable for large-scale genetic studies in maize. GBS has been successfully applied to various maize populations, including association populations, backcross generations, double haploids, and recombinant inbred lines. This technique generates a substantial number of SNPs, although it often results in high rates of missing data, which can be mitigated through imputation methods. GBS is particularly beneficial for genetic diversity analysis, linkage mapping, and genomic prediction, making it a versatile tool in maize breeding programs (Elbasyoni et al., 2018; Wang et al., 2020; Munyengwa et al., 2021). 2.2 Single nucleotide polymorphism (SNP) arrays SNP arrays are another powerful tool for maize breeding, providing high-quality genotyping data. Although SNP arrays are more expensive per sample compared to GBS, they offer high accuracy and consistency. SNP arrays have been used to develop high-density genetic maps and perform genome-wide association studies (GWAS) in maize. These arrays facilitate the identification of genetic patterns and population structures, which are crucial for genomic selection and marker-assisted selection、 2.3 Whole-genome sequencing (WGS) Whole-Genome Sequencing (WGS) provides comprehensive genotyping data by sequencing the entire genome. This method is highly accurate and can identify millions of genetic markers, making it ideal for fine mapping and high-resolution GWAS. However, WGS is costly, especially when applied to large populations. Despite its expense, WGS is invaluable for constructing high-density genetic maps and understanding the genetic basis of complex traits in maize (Elbasyoni et al., 2018; Rice and Lipka, 2021; Chen et al., 2021). 2.4 Marker-assisted selection (MAS) Marker-Assisted Selection (MAS) involves using molecular markers linked to desirable traits to select individuals in breeding programs. MAS has been widely used in maize breeding to improve traits such as yield, disease resistance, and abiotic stress tolerance. The integration of MAS with other genomic technologies, such as QTL mapping and RNA-sequencing, has enhanced the efficiency of selecting superior genotypes. MAS is particularly effective for traits controlled by major QTLs, providing a targeted approach to breeding (Torkamaneh et al., 2021). 2.5 Genomic selection (GS) Genomic Selection (GS) is a cutting-edge approach that uses genome-wide marker data to predict the breeding values of individuals. GS has revolutionized maize breeding by increasing genetic gains and reducing the number of breeding cycles required to develop new varieties. This method captures both major and minor genetic effects, making it suitable for complex traits. GS models have been refined to account for non-additive genetic effects, genotype-by-environment interactions, and other factors, further improving prediction accuracy. The integration of high-throughput phenotypic and genotypic data has made GS a powerful tool for accelerating maize breeding programs. By leveraging these genomic technologies, maize breeders can achieve significant improvements in crop performance, ensuring food security and sustainability in agriculture (Guo et al., 2019; Rice and Lipka, 2021; Merrick et al., 2022).
Maize Genomics and Genetics 2024, Vol.15, No.3, 111-122 http://cropscipublisher.com/index.php/mgg 113 3 Techniques in Genomics-Assisted Breeding 3.1 Quantitative trait loci (QTL) mapping QTL mapping is a fundamental technique used to identify genomic regions associated with specific phenotypic traits. This method involves crossing two genetically distinct lines to produce a mapping population, which is then genotyped and phenotyped to detect QTLs. For instance, QTL mapping has been instrumental in identifying loci associated with yield-related traits in maize, such as kernel weight and ear length (Zhao and Su, 2019). Additionally, meta-analysis of QTLs has been used to identify stable QTLs for traits like popping quality and disease resistance, which are crucial for marker-assisted selection (Kaur et al., 2021; Akohoue and Miedaner, 2022). 3.2 Genome-wide association studies (GWAS) GWAS is a powerful approach that scans the entire genome to find genetic variants associated with traits of interest. This method utilizes high-density SNP arrays and large, diverse populations to detect associations between genetic markers and phenotypic traits. For example, GWAS has been used to identify SNPs linked to yield-related traits and kernel micronutrient concentrations in maize (Hindu et al., 2018; Zhang et al., 2020). Multi-trait GWAS approaches have also been effective in uncovering pleiotropic QTLs that influence multiple traits simultaneously, enhancing our understanding of complex trait architecture (Rice et al., 2020). 3.3 Transcriptomics and RNA-seq Transcriptomics, particularly RNA-Seq, provides insights into gene expression patterns and regulatory networks underlying phenotypic traits. This technique involves sequencing the RNA transcripts in a sample to quantify gene expression levels. RNA-Seq has been used to validate candidate genes within QTL regions and to understand the genetic basis of traits such as kernel width and disease resistance (Zhao et al., 2022). By integrating transcriptomic data with QTL mapping, researchers can identify differentially expressed genes that contribute to trait variation. 3.4 CRISPR/Cas9 and gene editing CRISPR/Cas9 is a revolutionary gene-editing technology that allows precise modifications of the genome. This technique has been applied to create targeted knockouts and insertions in maize, facilitating the study of gene function and the improvement of complex traits. For instance, the BREEDIT pipeline combines CRISPR/Cas9-mediated multiplex genome editing with traditional breeding to enhance traits like yield and drought tolerance (Lorenzo et al., 2022) (Figure 1). This approach accelerates the development of improved maize varieties by enabling the precise manipulation of multiple genes simultaneously. Lorenzo et al. (2022) presents an innovative CRISPR/Cas9 multiplex genome editing pipeline designed to enhance maize growth by targeting 48 growth-related genes (GRGs). It employs a sophisticated approach that combines multiple gRNAs into vectors (SCRIPTs) and transforms Cas9-expressing lines (EDITOR lines) to create supertransformed plants. These plants undergo various crossing schemes to maximize the diversity of gene edits. High-throughput sequencing and bioinformatics workflows monitor gene edits, classify them into loss-of-function (LOF) categories, and facilitate genotype-to-phenotype associations. This method enables the systematic evaluation of the effects of multiple gene edits on plant growth, ultimately identifying key genes that significantly influence growth traits. The study demonstrates the potential of this pipeline to generate a large collection of higher-order mutants, providing a valuable resource for future research and trait improvement in maize. 3.5 Epigenomics Epigenomics involves the study of heritable changes in gene expression that do not involve changes to the DNA sequence. These changes can be influenced by environmental factors and can affect traits such as stress tolerance and disease resistance. Epigenomic studies in maize have the potential to uncover novel regulatory mechanisms and epigenetic markers that can be used in breeding programs. Although specific studies on epigenomics in maize are less prevalent, integrating epigenomic data with other genomic techniques can provide a comprehensive understanding of trait regulation and inheritance. In summary, genomics-assisted breeding in maize employs a suite of advanced techniques to dissect the genetic basis of important traits and to accelerate the development of improved varieties. By integrating QTL mapping,
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