Molecular Plant Breeding 2024, Vol.15, No.5, 282-294 http://genbreedpublisher.com/index.php/mpb 283 from its wild progenitor, teosinte, to the modern varieties we see today (Figure 1) (Chen et al., 2020). This process of domestication was driven by human selection for traits that improved yield, ease of harvest, and adaptability to different environments. The early breeding efforts were largely empirical, relying on the visual selection of superior plants and seeds, which provided scientific evidence for more systematic breeding approaches in later centuries. Figure 1 Crucial morphological changes during maize and rice domestication and the underlying key genes (Adopted from Chen et al., 2020) Image caption: Top, wild rice to cultivated rice; bottom, teosinte to maize (Adopted from Chen et al., 2020) 2.2 Limitations of conventional breeding methods Conventional breeding methods, including hybridization and selective breeding, have been instrumental in improving maize yields and adaptability. However, these methods have several limitations. One major limitation is the time required to develop new varieties, as multiple generations of crossing and selection are needed to achieve desired traits. Additionally, conventional breeding relies heavily on phenotypic selection, which can be influenced by environmental factors, making it challenging to accurately select for genetic traits (Zhou and Xu, 2024). Hybridization, while effective in exploiting hybrid vigor, often requires extensive resources and labor to produce hybrid seeds. Furthermore, conventional methods are limited in their ability to introduce new traits from distant or wild relatives due to reproductive barriers and linkage drag, where undesirable traits are co-inherited with desirable ones (Muntean et al., 2022). 2.3 Successes and challenges in traditional maize improvement Traditional maize breeding has achieved significant successes, particularly in the development of high-yielding hybrid varieties. The introduction of hybrid maize in the early 20th century led to dramatic increases in yield and productivity, contributing to food security and agricultural sustainability. The Green Revolution further exemplified the success of traditional breeding, with the development of semi-dwarf, high-yielding varieties that transformed agriculture in many parts of the world. However, these successes have not been without challenges. One of the ongoing challenges is the need to continuously develop new varieties that can withstand biotic and abiotic stresses, such as pests, diseases, and climate change (Nepolean et al., 2018; Muntean et al., 2022).
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