Maize Genomics and Genetics 2024, Vol.15, No.2, 70-79 http://cropscipublisher.com/index.php/mgg 74 5.2 Breeding for stress resistance and adaptability Breeding for stress resistance and adaptability is essential for ensuring the sustainability of maize production under various environmental stresses. Studies have identified specific genes and pathways that confer resistance to biotic and abiotic stresses, such as drought, low nitrogen, soil acidity, and pest and disease resistance (Wen et al., 2011; Abdoul-Raouf et al., 2017). For example, the use of wild relatives like teosinte and Tripsacum has been instrumental in introducing genes that confer tolerance to chlorotic dwarf virus, downy mildew, Fusarium, Striga hermonthica, rootworms, drought, and flooding (Abdoul-Raouf et al., 2017). Additionally, genomic studies have revealed signatures of selection for traits like heat tolerance and tick resistance in African cattle, which can be analogous to similar efforts in maize breeding (Kim et al., 2017). 5.3 Enhancing yield and nutritional quality Improving grain yield and nutritional quality remains a primary goal in maize breeding. The genetic architecture of maize ear traits, which significantly influence yield, has been dissected using multiple populations and high-density markers. This approach has identified numerous quantitative trait loci (QTLs) that can be targeted for yield improvement. Furthermore, the genetic diversity within maize and its wild relatives can be exploited to enhance nutritional quality by introducing alleles that improve the content of essential nutrients (Whitt et al., 2002; Chen et al., 2021). The integration of these diverse genetic resources into breeding programs can lead to the development of high-yielding and nutritionally superior maize varieties. 5.4 Genomic selection and modern breeding techniques Genomic selection and other modern breeding techniques have revolutionized maize breeding by increasing selection intensity and accelerating the breeding cycle. Genomic prediction models, which use marker effects to predict hybrid performance, have shown promise in improving traits such as grain yield, anthesis date, and anthesis-silking interval (Windhausen et al., 2012). However, the effectiveness of these models depends on the genetic relationship between the training and validation sets, as well as the population structure (Windhausen et al., 2012). Additionally, the use of high-density genomic variation maps and genome-wide association studies (GWAS) can facilitate the identification of adaptive variants and the fine mapping of QTLs, thereby enhancing the precision and efficiency of breeding programs (Chen et al., 2021). In conclusion, the genetic diversity within Zea species provides a valuable resource for maize breeding programs. By leveraging this diversity, breeders can develop new varieties with improved stress resistance, adaptability, yield, and nutritional quality. Modern breeding techniques, including genomic selection and GWAS, further enhance the potential for achieving these goals, ultimately contributing to the sustainability and productivity of maize agriculture. 6 Case Studies 6.1 Successful breeding programs utilizing zea genetic diversity Several breeding programs have successfully utilized the genetic diversity of Zea to enhance crop performance and resilience. For instance, the breeding program in Sichuan province, Southwest China, has leveraged the genetic diversity and population structure of 157 elite maize inbred lines to improve hybrid production. This program identified four distinct genetic groups, which facilitated the strategic use of germplasm in hybrid breeding, leading to better exploitation of heterotic patterns (Leng et al., 2019). Similarly, the International Maize and Wheat Improvement Center (CIMMYT) has investigated the genetic diversity among tropical lowland inbred lines using SSR markers. This study revealed a lack of structure within the germplasm, which can be attributed to the mixed origin of the populations used. The findings support the choice of representative testers for evaluating inbred lines, thereby enhancing the exploitation of genetic diversity in hybrid breeding (Xia et al., 2004). 6.2 Conservation projects in different regions Conservation projects across various regions have focused on preserving the genetic diversity of Zea species. In Mexico, the genetic diversity of wild maize (teosinte) has been studied to understand the effects of historical climate fluctuations on genetic diversity. This research highlighted the significant genetic structure among populations and the influence of local adaptation and genetic isolation on current genetic diversity (Figure 2)
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