Maize Genomics and Genetics 2025, Vol.16, No.3, 108-118 http://cropscipublisher.com/index.php/mgg 113 means such as quantitative trait loci (QTL) positioning and genome-wide association analysis (GWAS) have played an important role in identifying potential QTLs and dominant genes, which can be introduced into excellent varieties to enhance their heat tolerance (El-Sappah et al., 2022; Djalović et al., 2023). For example, the study by Seetharam et al. (2021) identified important single nucleotide polymorphisms (SNPs) associated with grain yield under heat stress, highlighting the genetic diversity in tropical corn germplasm and providing valuable genetic resources for heat-resistant breeding. In addition, the study by Inghelandt et al. (2019) showed that in temperate maize, QTL mapping technology has been used to evaluate phenotypic and genotypic diversity related to heat tolerance, revealing multiple specific QTLs related to heat tolerance, providing important molecular markers for heat-resistant breeding. 5.2 Integration of genomic tools and molecular breeding technology The latest research of Jiang Haiyang's team in the National and Local Joint Engineering Laboratory for Crop Stress Breeding and Disaster Reduction, College of Life Sciences, Anhui Agricultural University on high temperature resistant corn breeding highlights the integrated application value of genomics and modern biotechnology. The research team used high-throughput sequencing technology to conduct genome-wide association analysis (GWAS) and discovered multiple key genes that regulate heat stress response, such as encoding heat shock proteins (HSPs), antioxidant enzymes and osmotic regulatory proteins. Gene editing technologies (such as CRISPR/Cas9) have been applied to the precise regulation of functional genes, and multiple heat-resistant mutants have been successfully obtained, which has improved the survival rate and photosynthetic efficiency of materials under high temperature conditions. These studies not only promoted the analysis of the genetic basis of maize heat tolerance, but also provided technical support for directional breeding. 5.3 Hybrid breeding and germplasm innovation Hybrid breeding is a traditional method of using hybrid vigor in corn, which can improve corn yield and pest and disease resistance. In hybrid breeding, parents need to be selected for hybridization to obtain excellent offspring. The key to hybrid breeding is to select suitable parents. In general, varieties with excellent economic traits should be selected as parents. Among the hybrid offspring, some hybrids with excellent traits can be obtained, which usually have higher yields and stronger resistance than purebreds. Stacked heterosis refers to the production of more hybrids through multiple hybridizations on the basis of hybrid breeding, thereby improving yield and quality. This method can further improve hybrid vigor, thereby improving corn yield and quality. The key to stacking heterosis is to select suitable parents for hybridization, and at the same time pay attention to mating protection to avoid adverse effects. The development of heat-resistant hybrids (such as ZD309) shows that combining the genetic advantages of parental lines can enhance adaptability to heat stress (Liu et al., 2022). Germplasm improvement is the genetic improvement of a certain type of germplasm to form better germplasm materials, which has a broader meaning. Germplasm innovation emphasizes innovation and creates new traits or new groups. For example, high-oil corn is a classic germplasm innovation work. There was no high-oil corn in the world, but it was formed through continuous gene aggregation. By collecting domestic and foreign germplasm resources, we carry out precise identification targeting production needs and industrial needs, and screen out breeding materials that are urgently needed for breeding, such as high salt-alkali tolerance materials, high protein, and high oil materials. Using modern breeding methods such as key genes or gene editing, we can create some new variants or new materials that are difficult to obtain in nature. The development of modern breeding technology provides such opportunities. 6 Case Studies of Heat Tolerance in Maize 6.1 High-temperature resilience in tropical and temperate maize varieties In recent years, the Chongqing Academy of Agricultural Sciences has been deeply promoting agricultural breeding research projects, strengthening the construction of the core germplasm resource bank of corn, and focusing on screening local varieties and breeding materials that perform well in high temperature environments. In 2024, Dong Xin, an associate researcher at the Institute of Corn and Specialty Crops of the Academy, participated in a major breakthrough in the study of corn heat resistance, successfully determining the key
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