Maize Genomics and Genetics 2024, Vol.15, No.2, 80-92 http://cropscipublisher.com/index.php/mgg 81 2 Origins of Maize in Southern Mexico 2.1. Genetic evidence for the domestication of maize The genetic evidence for the domestication of maize points to a single origin in southern Mexico, where its wild ancestor, teosinte (Zea mays ssp. parviglumis), was domesticated (Heerwaarden et al., 2010; Panda et al., 2020). Genetic studies have consistently supported this theory, indicating that maize underwent a domestication event approximately 9 000 years ago in this region. Molecular analyses, including those of isozymes and chloroplast DNA, provide strong support for the hypothesis that teosinte is ancestral to maize. These studies have shown that populations of teosinte from the central Balsas River Valley in Mexico exhibit the closest genetic relationship to modern maize (Doebley, 1990). Further research has revealed that during domestication, a significant genetic bottleneck occurred, reducing genetic diversity in maize compared to its wild relatives. This bottleneck is evidenced by the reduced genetic variability observed in domesticated maize when compared to teosinte (Vallebueno-Estrada et al., 2016). Genomic studies also highlight the role of artificial selection in shaping maize’s genetic makeup, with approximately 2% of maize genes showing signs of artificial selection, primarily related to traits advantageous for cultivation and yield (Yamasaki et al., 2007). 2.2 Archaeological findings related to early maize cultivation Archaeological evidence supports the genetic findings by indicating early maize cultivation in southern Mexico. Macro- and microbotanical evidence, including maize pollen and phytoliths, has been found in sediment layers dating back to approximately 8 700 years ago. These findings suggest that maize was one of the first domesticated crops in the region and played a crucial role in the development of early agricultural societies. Significant archaeological sites such as Guilá Naquitz and San Marcos Cave have yielded early maize cobs and other botanical remains, which provide concrete evidence of early cultivation practices. These sites illustrate the transition from wild to domesticated maize, highlighting the gradual process of selecting for desirable traits over generations (Aguirre-Liguori et al., 2016). 2.3 The role of Southern Mexico in the initial domestication process Southern Mexico, particularly the Balsas River Valley, is recognized as the primary center of maize domestication. This region’s unique environmental conditions and the presence of wild teosinte provided the ideal setting for the initial domestication process. Genetic evidence indicates that the domestication of maize was a single event rather than multiple independent events, underscoring the significance of southern Mexico in this agricultural milestone (Doebley, 1990). The role of southern Mexico in maize domestication is further emphasized by studies on genetic introgression. As domesticated maize spread to different regions, it occasionally hybridized with local wild teosinte populations, incorporating beneficial traits that allowed maize to adapt to diverse environments. This genetic exchange facilitated the spread of maize to higher elevations and different climatic zones, demonstrating the adaptability and resilience of this crop (Aguirre-Liguori et al., 2016). The genetic and archaeological evidence converges on southern Mexico as the cradle of maize domestication. The genetic data indicate a single domestication event in this region, while archaeological findings provide tangible proof of early cultivation practices. The initial domestication process in southern Mexico set the stage for maize to become a globally significant crop, underlining the importance of this region in agricultural history. 3 Genetic Perspectives on Maize Spread 3.1 Analysis of maize genetic diversity and its implications Maize (Zea mays) exhibits significant genetic diversity, which has profound implications for its cultivation, adaptation, and improvement. The genetic diversity within maize is a product of both its domestication history and subsequent breeding practices. This diversity is critical for the crop's ability to adapt to various environmental stresses and changing climatic conditions.
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