Maize Genomics and Genetics 2024, Vol.15, No.4, 182-190 http://cropscipublisher.com/index.php/mgg 186 genetic diversity post-2000, likely due to the introgression of beneficial alleles from MVs (Rojas-Barrera et al., 2019). This enhanced genetic diversity is vital for the evolutionary capacity of maize populations to adapt to novel environments, as evidenced by the retention of 99% of the standing molecular marker variation in a population subjected to directional selection for flowering time adaptation (Wisser et al., 2019). 5.2 Evolution of agronomic traits Gene flow significantly influences the evolution of agronomic traits in maize. The introgression of alleles from MVs into LRs and WRs can lead to rapid changes in traits such as flowering time, yield, and drought resistance. For example, a high-resolution genome-wide association study identified hundreds of candidate genes associated with genotype by environment interactions, which are crucial for agronomic performance across diverse environments (Gates et al., 2019). Additionally, the domestication process of maize, which involved the transformation of teosinte into modern maize, was driven by genetic interactions and selection pressures that shaped key agronomic traits (Stitzer et al., 2018). These findings underscore the importance of gene flow in the ongoing evolution and improvement of agronomic traits in maize. 5.3 Pest and disease resistance Gene flow also has implications for pest and disease resistance in maize. The introduction of alleles from MVs into LRs and WRs can enhance resistance to pests and diseases, which is critical for crop sustainability. The genomic evidence of ongoing evolution in maize due to introgression from MVs suggests that beneficial alleles conferring resistance to biotic stresses may be incorporated into the genetic pool of LRs and WRs (Rojas-Barrera et al., 2019). This process can lead to the development of maize varieties with improved resistance to pests and diseases, thereby reducing the reliance on chemical control methods and promoting sustainable agricultural practices. 5.4 Conservation and biodiversity The conservation of genetic diversity and biodiversity in maize is closely linked to gene flow. The introgression of alleles from MVs into LRs and WRs not only enhances genetic diversity but also contributes to the conservation of these genetic resources. Monitoring strategies and policies that promote the use and safeguarding of genetic diversity are essential for the conservation of maize at its center of origin (Rojas-Barrera et al., 2019). Furthermore, understanding the evolutionary dynamics of maize populations, including the role of gene flow, is crucial for developing effective conservation strategies that ensure the long-term sustainability of maize biodiversity (Stitzer et al., 2018; Rojas-Barrera et al., 2019; Gates et al., 2019). 6 Case Studies 6.1 Gene flow in modern agricultural landscapes Gene flow in modern agricultural landscapes has been a significant factor influencing the genetic diversity and evolution of maize. Contemporary studies have shown that the introduction of modern maize varieties (MVs) into traditional agricultural systems can lead to rapid genetic changes in indigenous landraces (LRs) and crop wild relatives (WRs). For instance, research conducted in Mexico, the center of origin for maize, demonstrated that gene flow from MVs has resulted in notable genomic changes in both LRs and WRs over the past 60 years. This gene flow has led to increased genetic diversity in LRs and a decrease in genetic divergence between MVs and both LRs and WRs, highlighting the dynamic nature of maize evolution in response to agricultural practices (Rojas-Barrera et al., 2019). Figure 2 illustrates the clustering of modern varieties (MV1 and MV2) with landraces collected during different periods (earlier than 1960, between 1960 and 1980, and later than 2000) and their genetic interactions as revealed by genotyping data. The clustering patterns shown in panels Figure 2A and 2B of the figure reflect the genetic integration of these maize varieties across different time frames and geographical distributions, which supports the study’s findings on the impact of gene flow on maize diversity and its adaptability to various agricultural environments (Rojas-Barrera et al., 2019). 6.2 Impact of transgenic maize on wild relatives The impact of transgenic maize on wild relatives is a critical area of study, particularly concerning the potential for gene flow and its ecological consequences. Transgenic maize varieties, designed for traits such as pest
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