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.2 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 Conventional Breeding vs. Genetic Engineering in Maize: A Comparative Study Jin Zhou, Limin Xu Maize Genomics and Genetics, 2024, Vol. 15, No. 2, 49-59 The Impact of Genetic Engineering on Maize Herbicide Tolerance Jiayi Wu, Qian Li Maize Genomics and Genetics, 2024, Vol. 15, No. 2, 60-69 Genetic Structure and Diversity in Zea Genus: Implications for Conservation and Breeding Yunfei Cai, Bin Chen, Junfeng Hou, Fucheng Zhao, Guiyue Wang, Renxiang Cai Maize Genomics and Genetics, 2024, Vol. 15, No. 2, 70-79 The Spread of Maize from Southern Mexico: Genetic and Archaeological Perspectives Jiansheng Li Maize Genomics and Genetics, 2024, Vol. 15, No. 2, 80-92 Genetic and Environmental Factors Influencing Grain Quality in Maize Xingzhu Feng Maize Genomics and Genetics, 2024, Vol. 15, No. 2, 93-101
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 49 Research Report Open Access Conventional Breeding vs. Genetic Engineering in Maize: A Comparative Study Jin Zhou, Limin Xu Hainan Provincial Key Laboratory of Crop Molecular Breeding, Sanya, 572025, Hainan, China Corresponding author: limin.xu@hitar.org Maize Genomics and Genetics, 2024, Vol.15, No.2 doi: 10.5376/mgg.2024.15.0006 Received: 17 Jan., 2024 Accepted: 23 Feb., 2024 Published: 05 Mar., 2024 Copyright © 2024 Zhou and Xu, 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 J., and Xu L.M., 2024, Conventional breeding vs. genetic engineering in maize: a comparative study, Maize Genomics and Genetics, 15(2): 49-59 (doi: 10.5376/mgg.2024.15.0006) 1 Introduction Maize (Zea mays L.), also known as corn, is one of the most important cereal crops globally, serving as a staple food for millions of people and a critical feedstock for livestock. Originating in Central America, maize has been domesticated and cultivated for thousands of years, leading to the development of numerous varieties adapted to diverse climatic and soil conditions. Its significance extends beyond nutrition; maize is also a key industrial crop used in the production of biofuels, bioplastics, and other value-added products. The crop's versatility and economic value underscore its importance in global agriculture and food security (Wilkes, 2007) Abstract This study explores the comparative aspects of conventional breeding and genetic engineering in maize, highlighting their respective achievements, limitations, and future prospects. Conventional breeding has a long history of success, utilizing methods such as mass selection, hybridization, and mutation breeding to develop high-yielding and nutritionally enhanced maize varieties like hybrid maize and Quality Protein Maize (QPM). However, these methods are often time-consuming and resource-intensive. Genetic engineering, including technologies like CRISPR-Cas9 and recombinant DNA, offers precise and rapid genome modification, enabling the development of traits such as pest resistance, herbicide tolerance, and enhanced nutritional content. Significant achievements, such as Bt maize and glyphosate-resistant varieties, demonstrate the potential of genetic engineering to improve yield and reduce chemical inputs. The integration of conventional breeding and genetic engineering approaches can maximize their benefits, combining genetic diversity and adaptability with precision and efficiency. Future research should focus on integrated breeding programs, leveraging genomic and phenomic data, sustainable agricultural practices, and addressing ethical and regulatory issues to ensure equitable access to advanced breeding technologies. Keywords Conventional breeding; Genetic engineering; Maize improvement; CRISPR-Cas9; Hybrid maize . The breeding of maize has evolved considerably over the centuries, employing both conventional and modern techniques to enhance desirable traits such as yield, disease resistance, and stress tolerance. Conventional breeding methods, including mass selection, backcrossing, and hybridization, have been the cornerstone of maize improvement. These methods rely on the natural genetic variation within maize populations and involve selecting individuals with favorable traits to propagate the next generation. Hybrid breeding, which involves crossing two genetically diverse inbred lines to produce a hybrid with superior traits, has been particularly successful in increasing maize yields and improving agronomic performance (Dreher et al., 2003). In recent decades, advances in genetic engineering have introduced new possibilities for maize improvement. Techniques such as transgenic modification and CRISPR/Cas9 genome editing allow for the precise manipulation of maize DNA to introduce or enhance specific traits. Genetic engineering enables the transfer of genes between unrelated species, significantly broadening the genetic base available for crop improvement. This technology has been used to develop maize varieties with traits such as herbicide resistance, insect resistance, and enhanced nutritional content (Shou, 2003). This study aims to provide a comprehensive comparison between conventional breeding and genetic engineering in maize. It will explore the historical context and methodologies of each approach, evaluate their respective impacts on yield, stress tolerance, and disease resistance, and assess their roles in enhancing the nutritional quality
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 50 of maize. Furthermore, the study will discuss the economic and ecological implications of these breeding techniques, considering factors such as cost-effectiveness, speed of development, and sustainability. By synthesizing current research and case studies, this study seeks to highlight the strengths and limitations of conventional breeding and genetic engineering, offering insights into future directions for maize improvement. Ultimately, the goal is to inform breeding strategies that can ensure food security and agricultural sustainability in the face of global challenges. 2 Conventional Breeding in Maize 2.1 Historical development of conventional breeding The history of maize breeding is deeply rooted in traditional agricultural practices that date back thousands of years. Native Americans initially domesticated maize from its wild ancestor teosinte, through careful selection for desirable traits such as larger kernels and more robust plant architecture (Wilkes, 2007). Early farmers relied on mass selection, which involves selecting the best plants based on observable traits and using their seeds for the next planting season. The advent of scientific breeding methods in the early 20th century revolutionized maize improvement. Researchers such as George Shull and Edward East developed the concepts of hybrid vigor (heterosis) and inbred lines, leading to the creation of hybrid maize. Hybrid maize exhibited superior yields and uniformity compared to open-pollinated varieties, making it a cornerstone of modern agriculture. The widespread adoption of hybrid maize in the United States during the mid-20th century significantly boosted maize productivity and cemented its role as a staple crop (Dreher et al., 2003). 2.2 Techniques and methods 2.2.1 Selection Selection is the oldest form of plant breeding and involves choosing plants with desirable traits to propagate the next generation. There are two primary types of selection: mass selection and pure line selection. In mass selection, seeds from the best-performing plants are mixed and sown together, which can lead to gradual improvements in traits such as yield, disease resistance, and drought tolerance. Pure line selection, on the other hand, involves selecting the best plants and self-pollinating them to produce homozygous lines, which are then evaluated for performance (Dreher et al., 2003). 2.2.2 Hybridization Hybridization is the process of crossing two genetically distinct inbred lines to produce hybrid offspring with superior traits. This technique exploits hybrid vigor, where the resulting hybrids exhibit greater vigor, higher yields, and improved stress resistance compared to their parents. Hybrid maize breeding involves several steps: developing inbred lines through repeated self-pollination, evaluating their performance, and finally, crossing the best inbreds to produce hybrids (Dreher et al., 2003). 2.2.3 Mutation breeding Mutation breeding involves exposing seeds to physical or chemical mutagens to create genetic variations. These mutations can lead to new traits that may not exist in the natural population. Selected mutants with desirable characteristics are then propagated and integrated into breeding programs. Although mutation breeding is less common in maize compared to other techniques, it has been used to develop traits such as disease resistance and improved nutritional content (Goldstein et al., 2019). 2.3 Achievements and success stories Conventional breeding has achieved numerous successes in maize improvement. One of the most notable achievements is the development of high-yielding hybrid maize varieties, which have significantly increased maize production worldwide. For example, the introduction of single-cross hybrids in the mid-20th century resulted in maize yields doubling in the United States within a few decades (Wang et al., 2020).
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 51 Another success story is the development of Quality Protein Maize (QPM), which contains higher levels of essential amino acids lysine and tryptophan. This improvement addresses the nutritional deficiencies in populations relying on maize as a staple food. QPM varieties were developed using conventional breeding techniques and have been widely adopted in developing countries to combat malnutrition (Tandzi et al., 2017). Conventional breeding has also played a crucial role in developing maize varieties resistant to diseases and pests. For instance, resistance to maize streak virus, a major disease in sub-Saharan Africa, has been successfully incorporated into maize varieties through traditional breeding methods (Figure 1) (Masuka et al., 2017) . Figure 1 Maize streak virus (MSV) score plotted against year of entry into regional trials of (a) early open-pollinated varieties (OPVs) and (b) intermediate-late OPVs from regional trials between 1999 and 2011 (Adopted from Masuka et al., 2017) Image caption: These two graphs illustrate the relationship between MSV scores and the year of entry into regional trials. Graph a shows a slight increase in MSV scores from 1998 to 2012, but the change is not significant (y = 2.3139 + 0.0074x, ns), with data points widely dispersed. Graph b shows a significant decrease in MSV scores (y = 3.3998 - 0.0552x, p<0.001), indicating that MSV scores significantly decrease over the years, with data points more concentrated along the downward trend. This suggests that over time, MSV scores have a statistically significant decreasing trend (Adopted from Masuka et al., 2017) 2.4 Limitations and challenges Despite its successes, conventional breeding faces several limitations and challenges. One significant challenge is the time required to develop new varieties. The process of creating inbred lines and evaluating hybrids can take several years, delaying the introduction of improved varieties. Additionally, conventional breeding relies heavily on the natural genetic variation present in maize populations, which may limit the range of achievable improvements (Morris et al., 2003).
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 52 Another limitation is the environmental dependency of trait expression. Genotype by environment interactions can affect the performance of bred varieties, making it challenging to predict how new hybrids will perform under different growing conditions. This variability necessitates extensive field trials across multiple environments, further extending the breeding timeline (Burger et al., 2008). Moreover, conventional breeding is often resource-intensive, requiring significant investments in labor, land, and facilities for field trials and seed production. These costs can be prohibitive, especially for public breeding programs and smaller seed companies with limited budgets (Jumbo et al., 2011). In conclusion, while conventional breeding has been instrumental in the development and improvement of maize, it faces challenges that limit its efficiency and scope. Addressing these challenges through technological advancements and complementary breeding techniques will be essential to meet the future demands of global agriculture. 3 Genetic Engineering in Maize 3.1 Historical development of genetic engineering The history of genetic engineering in maize dates back to the late 20th century when scientists began to explore the potential of recombinant DNA technology. The first genetically modified (GM) maize plants were developed in the early 1980s using methods such as Agrobacterium-mediated transformation and particle bombardment. These techniques allowed for the introduction of foreign genes into the maize genome, enabling the development of transgenic maize with improved traits (Dunder et al., 1995). One of the earliest successes in genetic engineering was the development of Bt maize, which expresses a gene from the bacterium Bacillus thuringiensis. This gene produces a protein toxic to certain insect pests, significantly reducing the need for chemical pesticides and leading to widespread adoption of Bt maize in the mid-1990s (Wisniewski et al., 2002). Since then, genetic engineering has expanded to include traits such as herbicide resistance, drought tolerance, and enhanced nutritional content. 3.2 Techniques and methods 3.2.1 Recombinant DNA technology Recombinant DNA technology involves the manipulation of DNA to create new genetic combinations that are not found in nature. In maize, this technology typically involves the insertion of genes that confer desirable traits, such as resistance to pests or tolerance to herbicides. The process begins with the identification and isolation of the gene of interest, which is then inserted into a plasmid vector. This vector is introduced into maize cells using methods like Agrobacterium-mediated transformation or particle bombardment (Yadava et al., 2017). Agrobacterium-mediated transformation utilizes the natural ability of Agrobacterium tumefaciens to transfer DNA into plant cells. The bacterium carries a plasmid with the gene of interest, which integrates into the plant genome, allowing for stable genetic modification. Particle bombardment, or biolistics, involves shooting microscopic particles coated with DNA into plant cells. This method is particularly useful for maize, which can be challenging to transform using Agrobacterium due to its recalcitrant nature (Hong et al., 2019). 3.2.2 CRISPR-Cas9 and other genome editing tools CRISPR-Cas9 has revolutionized genetic engineering by enabling precise, targeted modifications to the genome. This system uses a guide RNA to direct the Cas9 enzyme to a specific DNA sequence, where it creates a double-strand break. The cell's natural repair mechanisms then fix the break, allowing for the introduction or deletion of specific genes. This technology offers several advantages over traditional recombinant DNA methods, including higher precision, fewer off-target effects, and the ability to make multiple simultaneous edits (Hue et al., 2018). Other genome editing tools, such as zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), also allow for precise genetic modifications. These technologies have been used to develop maize varieties with enhanced traits, such as improved drought tolerance and resistance to various pests and diseases (Yang and Yan, 2021).
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 53 3.3 Achievements and success stories Genetic engineering has led to several significant achievements in maize improvement. One of the most notable successes is the development of Bt maize, which has dramatically reduced the need for chemical insecticides and increased yields by protecting crops from pest damage. This has had profound economic and environmental benefits, especially for smallholder farmers in developing countries (Wisniewski et al., 2002). Another success story is the development of herbicide-resistant maize varieties. These varieties allow farmers to control weeds more effectively with fewer herbicide applications, reducing labor costs and promoting more sustainable farming practices. Glyphosate-resistant maize, for example, has been widely adopted and has significantly improved weed management in maize cultivation (Hong et al., 2019). Genetic engineering has also been instrumental in developing drought-tolerant maize varieties. By introducing genes that help plants manage water stress, researchers have created maize that can maintain yields under adverse conditions. This is particularly important in regions prone to drought, where crop failure can have devastating consequences for food security (Hue et al., 2018). 3.4 Limitations and challenges Despite its successes, genetic engineering in maize faces several limitations and challenges. One of the main challenges is public perception and regulatory hurdles. Genetically modified organisms (GMOs) are often viewed with suspicion by the public, and stringent regulatory requirements can delay the approval and commercialization of new GM maize varieties (Lemaux, 2008). Another limitation is the potential for unintended effects. While genome editing technologies like CRISPR-Cas9 offer high precision, off-target mutations can still occur, leading to unintended consequences. This necessitates thorough screening and validation of edited plants to ensure their safety and efficacy (Fu et al., 2021). Additionally, the high cost and technical expertise required for genetic engineering limit its accessibility, particularly for resource-poor farmers and developing countries. While the technology holds great promise, ensuring its benefits are widely distributed remains a significant challenge (Khan et al., 2012). Genetic engineering has significantly advanced maize breeding, providing solutions to some of the most pressing challenges in agriculture. However, addressing the limitations and overcoming the challenges associated with this technology will be crucial to fully realize its potential for improving maize production and sustainability. 4 Comparative Analysis 4.1 Efficiency and precision Conventional breeding and genetic engineering differ significantly in their efficiency and precision. Conventional breeding methods, such as selection and hybridization, rely on the natural genetic variation present within maize populations. These methods are relatively imprecise because they involve crossing plants and selecting offspring with desirable traits over multiple generations, which can introduce unwanted traits along with the desired ones (Burger et al., 2008). In contrast, genetic engineering, particularly with tools like CRISPR-Cas9, allows for precise modifications at specific locations within the genome. This precision minimizes the introduction of unwanted traits and speeds up the development of new varieties (Hue et al., 2018). 4.2 Time and resource investment The time and resources required for developing new maize varieties are considerably different between conventional breeding and genetic engineering. Conventional breeding is time-consuming, often taking 7-10 years to develop a new variety due to the multiple generations needed for selection and stabilization (Figure 2) (Morris et al., 2003) . Genetic engineering, however, can significantly shorten this timeline by directly introducing desired traits into the plant's genome, potentially reducing the development time to 3-5 years. The initial setup and technological investments for genetic engineering are higher, but the long-term benefits in speed and precision often justify these costs (Yadava et al., 2017).
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 54 Figure 2 Comparison of the flow of annual research net benefits generated by conventional and marker-assisted inbred line conversion schemes (Adopted from Morris et al., 2003) Image caption: The marker-assisted scheme (MAS-A) features larger up-front investment costs (larger negative annual net benefits in years 1-6), but because marker-assisted selection accelerates the line conversion process, varieties based on the converted line are released earlier and adoption by farmers occurs sooner. Positive annual net benefits generated by the marker-assisted line conversion scheme are therefore moved forward in time (Adopted from Morris et al., 2003) 4.3 Trait improvement and yield Both conventional breeding and genetic engineering have achieved significant improvements in maize traits and yield. Conventional breeding has successfully increased yields through hybridization and selection, focusing on traits like disease resistance, drought tolerance, and nutrient efficiency. Quality Protein Maize (QPM), which addresses nutritional deficiencies, is a notable success of conventional breeding (Tandzi et al., 2017). Genetic engineering has introduced traits such as Bt toxin for pest resistance and glyphosate resistance for herbicide tolerance, which have significantly enhanced yield stability and reduced reliance on chemical inputs (Wisniewski et al., 2002). 4.4 Environmental impact The environmental impacts of conventional breeding and genetic engineering are complex and context-dependent. Conventional breeding generally maintains broader genetic diversity within crop populations, which can enhance ecosystem resilience. However, it often relies on extensive field trials and the use of chemical inputs to manage pests and diseases. Genetic engineering can reduce environmental impact by decreasing the need for chemical pesticides and herbicides through the introduction of resistant traits (Hong et al., 2019). Nevertheless, there are concerns about potential gene flow from genetically modified crops to wild relatives and non-target species, which could have unforeseen ecological consequences (Weber et al., 2007). 4.5 Socio-economic considerations The socio-economic implications of conventional breeding and genetic engineering in maize are significant. Conventional breeding is often more accessible to resource-poor farmers and public breeding programs due to lower initial costs. It supports local agricultural practices and biodiversity by utilizing locally adapted varieties (Jumbo et al., 2011). Genetic engineering, while potentially more cost-effective in the long term, requires substantial initial investment in technology and expertise, which can be prohibitive for small-scale farmers.
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 55 Moreover, the patenting of genetically modified seeds by private companies can lead to issues of accessibility and control over seed distribution, impacting farmer autonomy and seed sovereignty (Khan et al., 2012). 4.6 Regulatory and safety issues Regulatory frameworks for conventional breeding and genetic engineering are markedly different. Conventional breeding is generally well-accepted and subject to standard agricultural regulations. Genetic engineering, however, faces stringent regulatory scrutiny to ensure safety and environmental compatibility. Concerns about the long-term health impacts and ecological risks of genetically modified organisms (GMOs) have led to rigorous testing and approval processes that can delay the release of new GM varieties (Lemaux, 2008). Additionally, public perception and acceptance of GMOs play a critical role in the adoption and success of genetically engineered crops. 5 Case Studies 5.1 Successful conventional breeding programs Conventional breeding has achieved numerous successes in maize improvement through the careful selection of desirable traits over many generations. One notable example is the development of Quality Protein Maize (QPM), which was bred to address protein deficiencies in populations that rely heavily on maize as a staple food. QPM varieties contain higher levels of essential amino acids lysine and tryptophan, significantly improving the nutritional value of maize (Tandzi et al., 2017). Another successful program is the participatory plant breeding initiative in Gujarat, India, which produced improved maize varieties through collaboration between farmers and breeders. This program resulted in the development of the variety GDRM-187, which showed better yield and grain quality than local landraces and was well-received by farmers for its early maturity and adaptability to local conditions. Conventional breeding efforts have also focused on developing maize varieties that are adapted to organic farming systems. Studies have shown that specific lines selected for organic conditions can perform comparably to those bred for conventional systems, demonstrating the versatility and effectiveness of traditional breeding methods (Burger et al., 2008). 5.2 Successful genetic engineering programs Genetic engineering has revolutionized maize breeding by introducing traits that were difficult or impossible to achieve through conventional methods. One of the earliest and most impactful examples is the development of Bt maize, which incorporates a gene from the bacterium Bacillus thuringiensis. This gene produces a protein toxic to certain insect pests, significantly reducing the need for chemical pesticides and leading to increased yields and lower environmental impact (Wisniewski et al., 2002). Another significant achievement is the development of herbicide-resistant maize varieties, such as those resistant to glyphosate. These varieties allow farmers to manage weeds more effectively and with fewer herbicide applications, promoting more sustainable agricultural practices (Hong et al., 2019). Recent advancements in CRISPR-Cas9 genome editing have further enhanced the potential of genetic engineering in maize. For instance, the BREEDIT pipeline combined multiplex genome editing with traditional breeding techniques to improve complex traits like yield and drought tolerance. This program successfully increased leaf length and width, demonstrating the potential for CRISPR to accelerate breeding processes and achieve significant genetic gains (Lorenzo et al., 2022). 5.3 Comparative case studies A comparative analysis of conventional breeding and genetic engineering in maize reveals unique advantages and limitations for each approach. Conventional breeding, exemplified by the development of QPM and participatory breeding programs in India, relies on the natural genetic variation within maize populations. These programs have produced varieties that are highly adapted to specific local conditions and nutritional needs, demonstrating the effectiveness of traditional methods in addressing complex agricultural challenges (Tandzi et al., 2017).
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 56 On the other hand, genetic engineering has achieved rapid and precise trait enhancements, as seen with Bt maize and herbicide-resistant varieties. These engineered crops have provided significant economic and environmental benefits by reducing the need for chemical inputs and increasing yield stability (Wisniewski et al., 2002; Hong et al., 2019). In a head-to-head comparison, marker-assisted selection (MAS) has been highlighted as a bridge between conventional and genetic engineering approaches. MAS allows breeders to select plants with desirable traits more efficiently by using molecular markers, enhancing the precision and speed of traditional breeding methods. Case studies at CIMMYT have shown that MAS can be cost-effective and time-saving compared to conventional breeding, particularly when visual selection is challenging (Dreher et al., 2003). Ultimately, both conventional breeding and genetic engineering play crucial roles in maize improvement. The choice of method depends on the specific goals, available resources, and the context in which the breeding program operates. Integrating both approaches, along with advancements like MAS and CRISPR, can provide a comprehensive strategy for addressing the diverse challenges in maize cultivation. 6 Future Prospects 6.1 Integration of conventional and genetic approaches The future of maize improvement lies in the integration of conventional breeding and genetic engineering techniques. Combining these approaches can maximize the strengths of each method while compensating for their individual limitations. Conventional breeding excels in leveraging natural genetic diversity and producing stable, locally adapted varieties. In contrast, genetic engineering provides the precision and speed necessary to introduce specific traits rapidly. Integrating marker-assisted selection (MAS) with traditional breeding can enhance the efficiency of selecting desirable traits by using molecular markers to track genes of interest (Mwamahonje and Mrosso, 2016). Moreover, CRISPR-Cas9 and other genome editing tools can be employed alongside conventional methods to introduce or modify genes with high precision, thus accelerating the breeding process. This integration allows for the development of maize varieties that combine multiple beneficial traits, such as high yield, disease resistance, and stress tolerance (Hue et al., 2018). 6.2 Innovations in breeding technologies The rapid advancement of breeding technologies promises to revolutionize maize improvement. Innovations such as genomic selection, which uses genome-wide markers to predict the breeding value of individuals, can significantly accelerate the breeding cycle and increase the accuracy of selecting high-performing plants (Andorf et al., 2019). Doubled haploid (DH) technology, which produces completely homozygous lines from a single cross within two generations, has become a cornerstone in maize breeding. This technology reduces the time required to develop pure lines and enhances the efficiency of breeding programs. Combining DH technology with CRISPR and other genetic engineering tools could lead to rapid development of maize varieties with complex trait improvements (Fischer and Edmeades, 2010). Additionally, advancements in phenotyping technologies, such as high-throughput phenotyping platforms and remote sensing, enable breeders to assess plant traits more accurately and efficiently. These tools, coupled with big data analytics and artificial intelligence, can provide deeper insights into the genetic basis of complex traits and optimize breeding strategies (Rosa et al., 2021). 6.3 Policy and ethical considerations As breeding technologies evolve, policy and ethical considerations will play a crucial role in their implementation and acceptance. Regulatory frameworks must adapt to accommodate new technologies, ensuring that genetically engineered crops are safe for the environment and human health. This involves stringent testing and monitoring to prevent unintended consequences and ensure transparency in the approval process (Barrows et al., 2014).
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 57 Ethical considerations include the accessibility of advanced breeding technologies to smallholder farmers and developing countries. Ensuring equitable access to these innovations is essential for addressing global food security challenges and preventing technological disparities. Public and private sectors must collaborate to create policies that support the dissemination of new varieties and technologies to all farmers, regardless of their economic status (Khan et al., 2012). Intellectual property rights (IPR) also pose significant challenges. While protecting the investments of researchers and companies is important, it is equally vital to ensure that IPR does not hinder the free exchange of germplasm and the adoption of beneficial technologies. Developing balanced IPR policies that encourage innovation while promoting accessibility and sharing of genetic resources is crucial (Jauhar, 2001). In conclusion, the future of maize breeding lies in the synergistic integration of conventional and genetic engineering approaches, leveraging innovations in breeding technologies, and addressing policy and ethical challenges. By adopting a holistic and inclusive approach, the potential of these technologies can be harnessed to meet the global demands for food security and sustainable agriculture. 7 Concluding Remarks This research has explored the comparative aspects of conventional breeding and genetic engineering in maize. Conventional breeding has a long history of success, exemplified by the development of hybrid maize and Quality Protein Maize (QPM), which have significantly improved yields and nutritional quality. Conventional methods, such as mass selection, hybridization, and mutation breeding, continue to play a crucial role in maize improvement. However, these methods are often time-consuming and resource-intensive. Genetic engineering, on the other hand, offers precise and rapid modification of the maize genome. Technologies like CRISPR-Cas9 and recombinant DNA have enabled the development of traits such as pest resistance, herbicide tolerance, and enhanced nutritional content. Genetic engineering has demonstrated significant achievements, including the development of Bt maize and glyphosate-resistant varieties, which have contributed to higher yields and reduced chemical inputs. The integration of both approaches can maximize the benefits of each, combining the genetic diversity and adaptability of conventional breeding with the precision and efficiency of genetic engineering. Future research should focus on integrating conventional and genetic engineering approaches to leverage the strengths of both methods. Specific recommendations include: Development of Integrated Breeding Programs: Establish programs that combine conventional breeding with marker-assisted selection and genome editing to enhance efficiency and precision in developing new maize varieties. Exploration of Genomic and Phenomic Data: Utilize advanced genomics and phenomics tools to better understand the genetic basis of complex traits and optimize breeding strategies. Sustainable Agricultural Practices: Research should aim to develop maize varieties that are resilient to climate change and capable of thriving under sustainable agricultural practices, reducing the environmental impact of maize cultivation. Public and Private Sector Collaboration: Foster collaborations between public research institutions and private companies to share resources, knowledge, and technologies, ensuring that advancements in maize breeding are accessible to all farmers. Addressing Ethical and Regulatory Issues: Conduct comprehensive studies on the ethical, environmental, and health implications of genetically modified maize, ensuring robust regulatory frameworks are in place to address public concerns.
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 58 The future of maize breeding and agriculture will depend on the successful integration of conventional breeding and genetic engineering. This hybrid approach can lead to the development of maize varieties that are higher yielding, more nutritious, and better adapted to environmental stresses. By combining the broad genetic base and adaptability provided by conventional breeding with the precision and speed of genetic engineering, breeders can address the challenges posed by climate change, population growth, and food security. Furthermore, sustainable maize breeding practices will contribute to environmental conservation by reducing the need for chemical inputs and enhancing the resilience of maize crops to biotic and abiotic stresses. Policymakers and stakeholders must support research initiatives, invest in new technologies, and create policies that promote the equitable distribution of advanced maize varieties. Acknowledgments The authors would like to express our gratitude to the two anonymous peer reviewers. Conflict of Interest Disclosure The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Andorf C.M., Beavis W.D., Hufford M., Smith S., Suza W.P., Wang K., Woodhouse M., Yu J.M., and Lübberstedt T., 2019, Technological advances in maize breeding: past, present and future, Theoretical and Applied Genetics, 132(3): 817-849. https://doi.org/10.1007/s00122-019-03306-3 PMid:30798332 Barrows G., Sexton S., and Zilberman D., 2014, Agricultural biotechnology: the promise and prospects of genetically modified crops, Journal of Economic Perspectives, 28(1): 99-120. https://doi.org/10.1257/jep.28.1.99 Burger H., Schloen M., Schmidt W., and Geiger H.H., 2008, Quantitative genetic studies on breeding maize for adaptation to organic farming, Euphytica, 163: 501-510. https://doi.org/10.1007/s10681-008-9723-4 Dreher K., Khairallah M., Ribaut J., and Morris M., 2003, Money matters (II): costs of maize inbred line conversion schemes at CIMMYT using conventional and marker-assisted selection, Molecular Breeding, 11: 235-247. https://doi.org/10.1023/A:1022820520673 Dreher K., Khairallah M., Ribaut J., and Morris M., 2003, Money matters (I): costs of field and laboratory procedures associated with conventional and marker-assisted maize breeding at CIMMYT, Molecular Breeding, 11: 221-234. https://doi.org/10.1023/A:1022820520673 Dunder E., Dawson J., Suttie J., and Pace G., 1995, Maize transformation by microprojectile bombardment of immature embryos, Bio/Technology, 4: 127-138. https://doi.org/10.1007/978-3-642-79247-2_15 Fischer R., and Edmeades G., 2010, Breeding and cereal yield progress, Crop Science, 50(s1): S85-S98. https://doi.org/10.2135/cropsci2009.10.0564 Fu W., Zhu P.Y., Qu M.N., Zhi W., Zhang Y.J., Li F.W., and Zhu S.F., 2021, Evaluation on reprogramed biological processes in transgenic maize varieties using transcriptomics and metabolomics, Scientific Reports, 11: 2050. https://doi.org/10.1038/s41598-021-81637-2 PMid:33479482 PMCid:PMC7820507 Goldstein W., Jaradat A., Hurburgh C.R., Pollak L.M., and Goodman M., 2019, Breeding maize under biodynamic-organic conditions for nutritional value and N efficiency/N2 fixation, Open Agriculture, 4(1): 322-345. https://doi.org/10.1515/opag-2019-0030 Hong J., Lee G. S., Park K., Kim J., Jang H.J., Suh E., Kim K.H., and Lee Y.H., 2019, Production of transgenic maize plants with herbicide resistance through agrobacterium-mediated transformation, Korean Journal of Breeding, 51(4): 290-297. https://doi.org/10.9787/KJBS.2019.51.4.290 Hue H., Linh N.T., and Ha N.H., 2018, Genetic engineering in developing drought tolerance maize and its new prospects, Vietnam Journal of Biotechnology, 16(1): 19-43. https://doi.org/10.15625/1811-4989/16/1/9317 Jauhar P.P., 2001, Genetic engineering and accelerated plant improvement: opportunities and challenges, Plant Cell, Tissue and Organ Culture, 64(2): 87-91. https://doi.org/10.1023/A:1010645813427 Jumbo M., Weldekidan T., Holland J., and Hawk J., 2011, Comparison of conventional, modified single seed descent, and doubled haploid breeding methods for maize inbred line development using germplasm enhancement of maize breeding crosses, Crop Science, 51: 1534-1543. https://doi.org/10.2135/cropsci2010.10.0594
Maize Genomics and Genetics 2024, Vol.15, No.2, 49-59 http://cropscipublisher.com/index.php/mgg 59 Khan M.H., Lone A., and Wani S.H., 2012, Genetic Engineering for Crop Improvement, INROADS-An International Journal of Jaipur National University, 1: 157-165. Lemaux P., 2008, Genetically engineered plants and foods: a scientist's analysis of the issues (part II), Annual Review of Plant Biology, 60: 511-559. https://doi.org/10.1146/annurev.arplant.043008.092013 PMid:19400729 Lorenzo C.D., Debray K., Herwegh D., Develtere W., Impens L., Schaumont D., Vandeputte W., Aesaert S., Coussens G., De Boe Y., Demuynck K., Van Hautegem T., Pauwels L., Jacobs T.B., Ruttink T., Nelissen H., and Inzé D., 2022, BREEDIT: a multiplex genome editing strategy to improve complex quantitative traits in maize, The Plant Cell, 35(1): 218-238. https://doi.org/10.1101/2022.05.02.490346 Masuka B., Magorokosho C., Olsen M., Atlin G., Bänziger, M., Pixley K., Vivek B., Labuschagne M., Matemba-Mutasa R., Burgueño J., Macrobert, J., Prasanna B., Das B., Makumbi D., Tarekegne A., Crossa J., Zaman-Allah M., Biljon A., and Cairns J., 2017, Gains in Maize genetic improvement in eastern and southern Africa: II. CIMMYT open-pollinated variety breeding pipeline, Crop Science, 57: 180-191. https://doi.org/10.2135/cropsci2016.05.0343 Morris M., Dreher K., Ribaut J., and Khairallah M., 2003, Money matters (II): costs of maize inbred line conversion schemes at CIMMYT using conventional and marker-assisted selection, Molecular Breeding, 11: 235-247. https://doi.org/10.1023/A:1022872604743 Mwamahonje A., and Mrosso L., 2016, Prospects of genetic modified maize crop in Africa, African Journal of Biotechnology, 15: 571-579. https://doi.org/10.5897/AJB2015.15098 Rosa T., Carvalho I., Hutra D.J., Bradebon L.C., Sarturi M.V.D.R., Gonzalez da Rosa J.A., and Szareski V.J., 2021, Maize breeding for abiotic stress tolerance: an alternative to face climate changes, Agronomy Science and Biotechnology, 6: 1-13. https://doi.org/10.33158/ASB.r119.v6.2020 Shou H., 2003, Crop improvement through genetic engineering: development of transformation technologies and production of stress tolerant transgenic crops. Dissertation, Iowa State University, Supervisor: Knapp A., pp.25-27. Tandzi L. N., Mutengwa C., Ngonkeu E., Woin N., and Gracen V., 2017, Breeding for quality protein maize (QPM) varieties: a review, Agronomy, 7: 80. https://doi.org/10.3390/agronomy7040080 Wang B.B., Lin Z.C., Li X., Zhao Y.P., Zhao B.B., Wu G.X., Ma X.J., Wang H., Xie Y.R., Li Q.Q., Song G.S., Kong D.X., Zheng Z.G., Wei H.B., Shen R.X., Wu H., Chen C.X., Meng Z.D., Wang T.Y., Li Y., Li X.H., Chen Y.H., Lai J.S., Hufford M.B., Ross-Ibarra J., He H., and Wang H.Y., 2020, Genome-wide selection and genetic improvement during modern maize breeding, Nat. Genet., 52: 565-571. https://doi.org/10.1038/s41588-020-0616-3 PMid:32341525 Wilkes G., 2007, Urgent notice to all maize researchers: disappearance and extinction of the last wild teosinte population is more than half completed, Maydica, 52: 49-58. Wisniewski J., Frangne N., Massonneau A., and Dumas C., 2002, Between myth and reality: genetically modified maize, an example of a sizeable scientific controversy, Biochimie, 84(11): 1095-1103. https://doi.org/10.1016/S0300-9084(02)00014-7 PMid:12595137 Yadava P., Abhishek A., Singh R., Singh, I., Kaul T., Pattanayak A., and Agrawal P., 2017, Advances in maize transformation technologies and development of transgenic maize, Frontiers in Plant Science, 7: 1949. https://doi.org/10.3389/fpls.2016.01949 PMid:28111576 PMCid:PMC5216042 Yang N., and Yan J., 2021, New genomic approaches for enhancing maize genetic improvement, Current Opinion in Plant Biology, 60: 101977. https://doi.org/10.1016/j.pbi.2020.11.002 PMid:33418269
Maize Genomics and Genetics 2024, Vol.15, No.2, 60-69 http://cropscipublisher.com/index.php/mgg 60 Research Report Open Access The Impact of Genetic Engineering on Maize Herbicide Tolerance Jiayi Wu, Qian Li Modern Agricultural Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China Corresponding author: qian.li@@cuixi.org Maize Genomics and Genetics, 2024, Vol.15, No.2 doi: 10.5376/mgg.2024.15.0007 Received: 24 Jan., 2024 Accepted: 01 Mar., 2024 Published: 10 Mar., 2024 Copyright © 2024 Wu and 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: Wu J.Y., and Li Q., 2024, The impact of genetic engineering on maize herbicide tolerance, Maize Genomics and Genetics, 15(2): 60-69 (doi: 10.5376/mgg.2024.15.0007) Abstract The adoption of genetically engineered maize for herbicide tolerance has significantly impacted agricultural practices, particularly in weed management. This study examines the development, implementation, and consequences of herbicide-tolerant maize varieties. The introduction of transgenic maize expressing genes such as dicamba monooxygenase (DMO) and CP4-EPSPShas enabled higher tolerance levels to herbicides like dicamba and glyphosate, respectively, leading to improved weed control and reduced crop injury. However, the widespread use of these genetically modified (GM) crops has also led to the emergence of herbicide-resistant weeds, necessitating the development of dual herbicide-tolerant varieties and new herbicide tolerance traits. Meta-analyses and field studies indicate that while GM crops have reduced overall pesticide use and increased crop yields and farmer profits, the long-term sustainability of these benefits is challenged by evolving weed resistance. This study synthesizes findings from multiple studies to provide a comprehensive understanding of the agronomic, economic, and environmental impacts of herbicide-tolerant maize, highlighting both the advantages and the ongoing challenges in this field. Keywords Genetic engineering; Herbicide tolerance; Maize (Zeamays); Weed resistance; Transgenic crops 1 Introduction Maize (Zea mays L.) is a staple crop with significant economic and nutritional importance worldwide. However, weed interference is a major biotic stress that can dramatically reduce maize yields. Effective weed management is crucial for maintaining favorable growing conditions and ensuring high crop productivity. Traditional weed control methods often rely on the application of herbicides, which can be labor-intensive and environmentally challenging. The development of herbicide-tolerant maize varieties through genetic engineering has emerged as a promising solution to enhance weed control efficiency and reduce the environmental impact of herbicide use (Perry et al., 2016; Larue et al., 2019). Herbicide-tolerant crops allow farmers to use specific herbicides that the crops can withstand, thereby effectively controlling weeds without damaging the crop itself. This technology has led to significant changes in agricultural practices, including reduced tillage, which helps in soil conservation and moisture retention. However, the widespread adoption of herbicide-tolerant crops has also raised concerns about the potential for increased herbicide use and the development of herbicide-resistant weed populations (Perry et al., 2016). Genetic engineering involves the manipulation of an organism's genome using biotechnology to introduce, enhance, or modify specific traits. In agriculture, genetic engineering has been used to develop crops with improved resistance to pests, diseases, and environmental stresses, as well as enhanced nutritional profiles. The introduction of herbicide tolerance traits in crops is one of the most successful applications of genetic engineering in agriculture (Fu et al., 2021). Several techniques are employed in the genetic engineering of crops, including the use of recombinant DNA technology to insert specific genes into the plant genome. For instance, the development of glyphosate-tolerant maize involves the insertion of the CP4-EPSPS gene, which confers resistance to the herbicide glyphosate. Similarly, the bar gene is used to develop glufosinate-tolerant maize. These genes are often introduced into the plant genome using Agrobacterium-mediated transformation or biolistic (gene gun) methods (Fu et al., 2021; Bonny, 2016; Bao et al., 2022).
Maize Genomics and Genetics 2024, Vol.15, No.2, 60-69 http://cropscipublisher.com/index.php/mgg 61 Recent advancements in genetic engineering have also focused on developing crops with multiple herbicide tolerance traits to address the issue of herbicide-resistant weeds. For example, maize varieties tolerant to both glyphosate and glufosinate have been developed to provide farmers with more flexible and effective weed management options (Fu et al., 2021; Bao et al., 2022). The primary objective of this study is to evaluate the impact of genetic engineering on herbicide tolerance in maize. Assess the effectiveness of genetically engineered herbicide-tolerant maize in improving weed control and crop yields. Examine the environmental and economic implications of adopting herbicide-tolerant maize varieties. Investigate the potential risks associated with the development of herbicide-resistant weeds and the increased use of herbicides. Explore the advancements in genetic engineering techniques that have contributed to the development of herbicide-tolerant maize. By synthesizing findings from multiple research studies, this study seeks to provide a comprehensive understanding of the benefits and challenges associated with genetically engineered herbicide-tolerant maize. The insights gained from this study will inform future research and policy decisions aimed at optimizing the use of genetic engineering in agriculture for sustainable crop production. 2 Genetic Engineering Techniques for Herbicide Tolerance 2.1 Genetic engineering techniques for herbicide tolerance Transgenic approaches involve the introduction of foreign genes into the maize genome to confer herbicide tolerance. One of the most common genes used in this context is the CP4-EPSPS gene, which provides resistance to glyphosate, a widely used broad-spectrum herbicide. For instance, the development of transgenic maize expressing both CP4-EPSPS and bar genes has shown significant tolerance to glyphosate and glufosinate, allowing for effective weed management and reducing the risk of herbicide resistance in weeds (Yu et al., 2023). Additionally, the use of codon-optimized synthetic CP4-EPSPS genes has been demonstrated to confer high levels of glyphosate tolerance in transgenic rice, suggesting similar potential applications in maize (Hummel et al., 2018). Genome editing techniques such as CRISPR/Cas9 and TALENs have revolutionized the field of genetic engineering by enabling precise modifications at specific genomic loci. CRISPR/Cas9, in particular, has been employed to introduce targeted mutations in the EPSPS gene, resulting in glyphosate-resistant crops. For example, CRISPR/Cas9-mediated homology-directed repair has been used to introduce amino acid substitutions in the EPSPS gene of rice, conferring glyphosate resistance and enhancing grain yield (Figure 1) (Sony et al., 2023). Similarly, the CRISPR/Cas9 system has been utilized to optimize glyphosate tolerance in rapeseed by precise gene replacement, demonstrating the potential for similar applications in maize (Wang et al., 2021). 2.2 Key genes involved in herbicide tolerance The EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene is a critical target for glyphosate, which inhibits the shikimate pathway essential for the biosynthesis of aromatic amino acids. Mutations in the EPSPS gene can render the enzyme less sensitive to glyphosate, thereby conferring resistance. For instance, the introduction of mutant variants of the EPSPS gene with specific amino acid substitutions has been shown to provide glyphosate tolerance in rice (Achary et al., 2020). Additionally, the co-expression of EPSPS with other genes, such as glyphosate oxidase, has been demonstrated to enhance glyphosate tolerance and reduce herbicide residues in transgenic crops (Wen et al., 2021). Apart from the EPSPS gene, other genes have also been identified to confer herbicide tolerance. For example, the bar gene, which encodes phosphinothricin acetyltransferase, provides resistance to glufosinate, another commonly used herbicide. The co-expression of CP4-EPSPS and bar genes in transgenic maize has been shown to confer dual herbicide tolerance, allowing for more flexible and effective weed management strategies (Yu et al., 2023). Additionally, the igrAgene from Pseudomonas, which encodes a glyphosate detoxifying enzyme, has been used in combination with EPSPS to enhance glyphosate tolerance and reduce herbicide residues in transgenic rice (Fartyal et al., 2018).
RkJQdWJsaXNoZXIy MjQ4ODYzNQ==