Maize Genomics and Genetics 2024, Vol.15, No.4, 171-181 http://cropscipublisher.com/index.php/mgg 172 improve modern maize, and the mechanisms by which these alleles can be integrated into maize breeding programs. By examining the current status and future prospects of utilizing teosinte in maize improvement, this study seeks to underscore the importance of conserving and studying wild germplasm to ensure the continued evolution and resilience of maize in the face of changing environmental conditions and agricultural demands. 2 Teosinte: Biological and Genetic Background 2.1 Taxonomy and species of teosinte Teosinte, the wild ancestor of modern maize (Zea mays L.), belongs to the genus Zea and comprises several species and subspecies. The primary taxa include Zea mays ssp. parviglumis, Zea mays ssp. mexicana, Zea diploperennis, Zea luxurians, Zea perennis, Zea mays ssp. huehuetenangensis, Zea vespertilio, and Zea nicaraguensis. These species are distributed from northern Mexico to Costa Rica, with the Mexican annuals Zea mays ssp. parviglumis and Zea mays ssp. mexicana showing a wide distribution in Mexico, while other species have more restricted ranges (González et al., 2018; Rivera-Rodríguez et al., 2023). 2.2 Morphological characteristics Teosinte exhibits distinct morphological traits compared to domesticated maize. It typically has a more branched structure with multiple stalks and smaller ears covered by a few layers of husks. The leaves of teosinte are generally narrower and longer than those of maize. The husk traits, including husk length, width, and the number of husk layers, show significant variation between teosinte and maize, with teosinte having fewer and smaller husk layers (Fu et al., 2019; Zhang et al., 2021). Additionally, teosinte kernels are encased in a hard fruitcase, unlike the exposed kernels of maize (Chen et al., 2020). 2.3 Genetic diversity in teosinte Teosinte harbors a high level of genetic diversity, which is crucial for its adaptation to various environmental conditions. Studies have shown that Zea mays ssp. parviglumis and Zea mays ssp. mexicana exhibit the highest levels of genomic diversity among the teosinte taxa (Rivera-Rodríguez et al., 2023). This genetic diversity is influenced by local adaptation to environmental factors such as temperature and soil phosphorus concentration, as well as historical climate fluctuations during the Holocene and Pleistocene (Aguirre-Liguori et al., 2019; Gasca-Pineda et al., 2023). The genetic structure of teosinte populations reveals significant differentiation between and within subspecies, driven by both contemporary and historical environmental factors (Gasca-Pineda et al., 2023). This diversity makes teosinte a valuable genetic resource for maize breeding programs aimed at improving traits such as stress tolerance and nutritional content (Figure 1) (Xu et al., 2019; Zavala-López et al., 2018). Figure 1 Metabolome divergence between maize and teosinte (Adopted from Xu et al., 2019) Image caption: (A): Classification of metabolites that have annotated structures; (B): Principal component analysis (PCA) of the maize and teosinte accessions with all metabolites (Adopted from Xu et al., 2019) 3 Historical Perspectives 3.1 Early studies on teosinte-maize relationships The relationship between teosinte and maize has been a subject of scientific inquiry for many years. Early studies focused on the morphological differences and similarities between the two plants. Teosinte, the wild ancestor of
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