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).
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