Maize Genomics and Genetics 2025, Vol.16, No.3, 119-128 http://cropscipublisher.com/index.php/mgg 123 system structure, nutritional efficiency, etc. In recent years, with the development of genomics technology, more and more studies have begun to focus on identifying QTL loci and functional genes related to heat resistance traits in wild species through genome comparative analysis and association studies. A key way to utilize local and wild germplasm resources is to build a genetic diversity evaluation system and a core germplasm bank. On this basis, modern breeding technologies such as molecular marker-assisted selection (MAS) and genome-wide association analysis (GWAS) are used to carry out targeted transfer and gene integration of target genes to improve breeding efficiency. For example, the research team of the Chinese Academy of Agricultural Sciences has constructed a genetic diversity pedigree map based on local germplasm and wild germplasm, providing important support for the discovery of heat-resistant genes in maize. 3.3 Molecular breeding technology Molecular marker-assisted selection (MAS) plays an important role in improving the heat tolerance of maize. By selecting specific genetic markers associated with heat tolerance traits, breeders can quickly identify and screen target traits at the molecular level, thereby accelerating the breeding process. MAS technology has helped locate key genomic regions and candidate genes associated with heat tolerance in multiple studies, providing technical support for the development of heat-resistant maize varieties. With the continuous development of molecular breeding technology, researchers have gradually revealed a number of important genes related to heat tolerance and their regulatory pathways. Genome-wide association analysis (GWAS) has been widely used to identify important SNP sites and candidate genes associated with heat stress resistance. For example, studies have found that heat shock transcription factors (Hsfs) and heat shock proteins (Hsps) play a key role in the heat tolerance response of sweet corn. In addition, the study also accurately located the genomic regions associated with heat stress resistance, providing a theoretical basis for the implementation of marker-assisted backcrossing and whole-genome selection in the future (Seetharam et al., 2021). 4 Molecular Marker-Assisted Breeding Technology 4.1 Study on the physiological mechanism and genetic improvement strategy of heat tolerance traits in maize With the increasing trend of global warming, high temperature stress has become one of the key factors restricting maize yield and production stability. The main impact of high temperature on maize is the destruction of photosynthesis and reproductive mechanisms, which in turn leads to a significant decrease in grain yield. Studies have shown that high temperature stress not only causes morphological changes such as slowing down the overall growth rate of maize, leaf burns, and reduced plant height, but also causes physiological disorders such as early flowering, prolonged pollen-silk interval (ASI), and decreased pollen vitality, which seriously affect pollination and fruiting rate (Alam et al., 2017; Hussain et al., 2019). In breeding practice, heat tolerance has become an important goal of maize genetic improvement. Studies have shown that high temperature stress mainly reduces the number of grains and fruiting rate by weakening pollen vitality, among which the silking time is relatively stable, but the fertilization ability of silking may be delayed due to high temperature. Therefore, improving the pollen viability and fertilization ability of maize under high temperature conditions is the core direction of improving heat tolerance. In recent years, the combination of molecular physiology and quantitative genetics has provided a theoretical basis for precision breeding of heat-resistant traits. For example, studies conducted under controlled environments revealed the molecular response mechanism of maize seedlings under heat stress, and subsequent phenotypic studies under field conditions further clarified the effects of heat stress on key agronomic traits. Frey et al. (2021) developed a heat sensitivity index to evaluate the response of different segregating families in temperate maize populations to heat stress, and located multiple important QTL loci related to heat tolerance on chromosomes 2 and 3. It is worth noting that the QTL on chromosome 3 is highly consistent with the region
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