Genomics and Applied Biology 2024, Vol.15, No.1, 12-21 http://bioscipublisher.com/index.php/gab 18 Gene knockout technology uses specific methods (such as transgenesis or mutagenesis) to inactivate target genes in the corn genome, and observe the impact of this genetic change on corn disease resistance. If the sensitivity of corn to a certain disease increases after knocking out a specific gene, it can be inferred that the gene plays a positive role in the disease resistance process. On the other hand, gene editing technology, especially the CRISPR/Cas9 system, plays an increasingly important role in the functional verification of corn disease resistance genes because of its efficient and precise gene site editing capabilities. By designing specific guide RNA (sgRNA), the CRISPR/Cas9 system can precisely introduce double-stranded breaks (DSBs) at target sites in the maize genome , thereby achieving knockout, knock-in or replacement of specific genes. This method can not only be used to verify the function of candidate genes identified by GWAS, but can also be directly used to create new corn varieties with disease resistance traits. Lee et al. (2020) used CRISPR/Cas9 technology to successfully knock out a gene related to disease resistance in corn. The results showed that the resistance of corn lines with the gene knocked out to specific diseases was significantly improved, verifying This gene plays a negative role in regulating corn disease resistance. In addition, Wang (2019) used CRISPR/Cas9 technology to edit another candidate disease resistance gene identified by GWAS, which also confirmed the key role of this gene in corn disease resistance. These studies not only confirmed the effectiveness of GWAS methods in identifying corn disease resistance genes, but also demonstrated the great potential of gene editing technology in functional verification and disease resistance breeding. Through these high-precision molecular biology techniques, researchers can gain a deeper understanding of the genetic basis of corn disease resistance, providing a powerful tool for future corn disease resistance breeding. 3.2 Molecular marker assisted selection (MAS) Genome-wide association studies (GWAS) in corn disease resistance breeding has significantly promoted the understanding and utilization of disease resistance genes. Molecular markers identified through GWAS provide a powerful tool for marker-assisted selection (MAS), which greatly improves the efficiency and accuracy of corn disease resistance breeding. MAS uses molecular markers to directly select individuals with desired genetic characteristics, and these markers are closely associated with corn disease resistance traits, thus bypassing the limitations of traditional breeding that rely on phenotypic selection. In the study of Shu et al. (2023), it was stated that southern corn rust (SCR) caused by Puccinia polycystis is the main disease causing serious yield reduction in China's summer corn belt. The study used six multilocus GWAS methods to identify a set of SCR resistance QTNs from a diverse set of 140 inbred lines collected in the Chinese summer maize belt. The 13 QTNs on chromosomes 1, 2, 4, 5, 6 and 8 were classified into three types of allelic effects, and they were verified through post-GWAS case-control sampling, allele/haplotype effect analysis Association with SCR phenotype (Figure 2). Figure 2 Manhattan plot of QTN resistance to southern corn rust (SCR) detected in 140 corn inbred lines by GWAS (Shu et al., 2023) Note: QTNs identified by multiple models are represented by pink dots with vertical lines; QTNs identified by a single model are represented by light green or blue dots with vertical lines. Gray leaf spot is a worldwide foliar disease of maize that can significantly reduce yields of susceptible genotypes. Research by Kuki et al. (2018) showed that gray leaf spot resistance is a complex trait controlled by multiple
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