Maize Genomics and Genetics 2025, Vol.16, No.6, 316-324 http://cropscipublisher.com/index.php/mgg 320 hormone signaling and defense metabolism (Long et al., 2022; Wang et al., 2024). This network framework, in other words, describes how environmental signals are ultimately transmitted to affect silk spinning and reproductive success, providing a complete set of ideas for subsequent heat-tolerant breeding. 6 Case Studies: QTL Divergence and Commonality Across Heat-Stressed Ecological Zones 6.1 Comparative analysis of QTLs in the North China Plain and Southeast Asia The expression of QTL varies in different ecological environments, which is particularly evident in the comparison between the North China Plain and Southeast Asia. In the North China Plain, studies on the recombinant inbred line (RIL) population have shown that there are hotspots on chromosomes 3, 8, 9 and 10 that control the number of days of silk production (DTS), the number of days of flowering (DTA) and ASI. Some regions, such as 118 MB-125 Mb on chromosome 8, Still stable under different stresses (Leng et al., 2022). However, when it comes to Southeast Asia, the situation is quite different. GWAS analysis revealed that although SNPS related to ASI, plant height and yield under high-temperature stress could also be detected, these markers often did not overlap much with those under normal conditions, and the environmental influence was significant (Longmei et al., 2021). That is to say, some QTLS are indeed highly adaptable, while others may only "work" in specific regions. 6.2 Validation of QTL stability in heat-sensitive and heat-tolerant varieties Not all QTLS can "stand firm" under all conditions. Often, stability is the key to whether they can be truly utilized by breeders. Some QTLS, such as mQTL2.2, mQTL6.1, mQTL7.5 and mQTL9.2, were repeatedly detected in the integrated analysis of 18 maize populations, and were all associated with yield and ASI, whether under water stress or adequate water conditions. However, such QTLS are only in the minority. The majority are either only effective under specific treatments or are significantly influenced by genetic background. Therefore, those loci that can maintain stable expression in both heat-sensitive and heat-tolerant varieties are more worthy of devoting efforts to MAS (Leng et al., 2022). 6.3 Environmental adaptation and breeding utility of precise QTLs across regions A QTL that can perform stably in different ecological zones is often the truly useful one. Meta-QTL and GWAS techniques can now compress the QTL region to a smaller size and directly identify core candidate genes including transcription factors and stress regulators, which is of great reference value for breeding in tropical and temperate regions (Figure 2) (Longmei et al., 2021; Djalovic et al., 2023). However, when using these QTLS, MAS and GS must also be combined to stably introduce heat-resistant alleles into superior materials, thereby maintaining yield performance under high-temperature conditions (Leng et al., 2022). It is worth noting that the trait of heat tolerance is inherently complex, with many genes involved and is also susceptible to environmental interference. Therefore, even if the QTL is precise, it still needs to be continuously verified and optimized in various regions. 7 Prospects and Strategies for QTL Application in Heat-Tolerant Breeding 7.1 Interaction mechanisms between key QTLs and traits such as yield and flowering time Some QTLS related to silk spinning under high-temperature stress are also frequently found in studies that control yield or flowering time. For instance, QTLS that affect ASI and DTA were simultaneously located on chromosomes 3, 8, and 9, and they manifested under both normal and stressful conditions (Zhang and Xu, 2024). This "overlap" may be due to pleiotropy or simply a chain relationship. In any case, they offer an opportunity to simultaneously regulate multiple important traits. But things are not that simple. Some QTL effects are indeed stable and applicable to multiple environments, while others are highly sensitive to the environment and change their appearance when conditions are altered. This is also why breeding programs are more inclined towards QTLS that have "stood firm" in multi-year trials in multiple locations (Du et al., 2021; Longmei et al., 2021). Stability might be more important than the size of the effect value.
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