Maize Genomics and Genetics 2024, Vol.15, No.3, 136-146 http://cropscipublisher.com/index.php/mgg 137 2 Sources of Genetic Diversity 2.1 Wild relatives and landraces Wild relatives and landraces of maize are crucial sources of genetic diversity, playing a significant role in crop improvement. The wild ancestor of maize, Teosinte, exhibits considerable phenotypic and genetic variation, including higher protein content and unique zein profiles compared to modern inbred lines and landraces (Flint-Garcia et al., 2009). Landraces, which are traditional maize varieties developed by farmers over many generations, harbor rich genetic diversity. For example, landraces from Morelos, Mexico, display significant genetic diversity and selection signatures across different municipalities. These landraces show notable phenotypic diversity and potential for genetic improvement in agronomic traits By comparing the genetic diversity of samples preserved in situ and ex situ, McLean-Rodríguez et al. revealed the geographical patterns of genetic variation and selection pressure, providing a scientific basis for the conservation and improvement of maize (Figure 1) (McLean-Rodríguez et al., 2021). Figure 1 Geographical distribution of the 93 ex situ samples collected in 1967 in Morelos state, Mexico (Kato 1967), with the 13 samples collected in situ for the genetic comparison with their ex situ counterparts in 2017 (Adopted from McLean-Rodríguez et al., 2021) Image caption: Figure 1 shows the geographic distribution of 93 ex situ samples collected in 1967 and 13 in situ samples resampled in 2017 from Morelos, Mexico. These samples represent maize landraces from different municipalities, providing detailed geographic references and information on the sample races. Different colors and shapes in the figure indicate the status of the samples in 2017 and their respective races, such as Ancho, Chalqueño, Cónico, Pepitilla, and Elotes Cónicos. Through these geographic distributions and sample descriptions, the study reveals genetic diversity and selection pressures in different regions. This figure demonstrates that landraces exhibit significant genetic variation across different geographic areas, highlighting the importance of in situ and ex situ conservation strategies in maintaining and utilizing maize genetic diversity. This information provides valuable scientific insights into the sources of genetic diversity in maize (Adopted from McLean-Rodríguez et al., 2021) 2.2 Germplasm banks and genetic resources Germplasm banks play a critical role in preserving and providing genetic resources for maize improvement. The International Maize and Wheat Improvement Center (CIMMYT) maintains a diverse collection of maize germplasm, including landraces, open-pollinated varieties (OPVs), and inbred lines adapted to non-temperate growing regions. These germplasm resources contain numerous unique alleles and represent a vast genetic reservoir for unexplored maize improvement (Warburton et al., 2008). Moreover, by collaborating with farmers, researchers can resample in situ conserved maize germplasm. These resources exhibit genome-wide diversity similar to ex situ preserved samples, demonstrating the importance and effectiveness of in situ conservation (McLean-Rodríguez et al., 2021).
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