Maize Genomics and Genetics 2024, Vol.15, No.4, 182-190 http://cropscipublisher.com/index.php/mgg 187 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 resistance and herbicide tolerance, can cross-pollinate with wild relatives, leading to the introgression of transgenes into wild populations. This gene flow can alter the genetic makeup of wild relatives, potentially affecting their fitness and ecological roles. Studies have shown that gene flow from transgenic maize to wild relatives like teosinte can occur, necessitating careful monitoring and management strategies to preserve the genetic integrity and ecological functions of wild maize relatives (Rojas-Barrera et al., 2019). 6.3 Adaptive introgression in different environments Adaptive introgression, the incorporation of beneficial alleles from one population into another through hybridization, plays a crucial role in the evolutionary dynamics of maize. Research has demonstrated that maize populations can rapidly adapt to new environments through the introgression of advantageous alleles. For example, a study on a tropical landrace of maize translocated to a temperate environment revealed significant genomic shifts over ten generations of selection for earlier flowering time. This adaptive introgression allowed the population to achieve a 26-day reduction in flowering time while maintaining high levels of genetic diversity, showcasing the potential for rapid environmental adaptation in maize (Wisser et al., 2019). 6.4 Comparative studies in other crops Comparative studies in other crops provide valuable insights into the evolutionary dynamics of gene flow and adaptation. For instance, research on crop wild relatives (CWRs) of woodland strawberry (Fragaria vesca) has highlighted the importance of natural selection, gene flow, and genetic drift in shaping genetic variation. These studies emphasize the need for an evolutionary approach to capture and conserve genetic diversity in CWRs, which can be applied to other crops like maize. By understanding the evolutionary processes in different crops, researchers can develop strategies to enhance crop resilience and adaptation to changing environments (Egan et al., 2018). 7 Future Directions 7.1 Advances in genomic technologies for gene flow studies The rapid evolution of genomic technologies has significantly enhanced our ability to study gene flow in maize. High-throughput sequencing and advanced genotyping methods, such as genotyping by sequencing (GBS), have provided detailed insights into the genetic changes occurring in maize populations over time. For instance, the use of GBS has revealed ongoing introgression from modern maize varieties (MVs) into landraces (LRs) and wild relatives (WRs), highlighting the dynamic nature of maize genomes in response to gene flow (Rojas-Barrera et al., 2019). Future advancements in genomic technologies, including more refined sequencing techniques and
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