Maize Genomics and Genetics 2025, Vol.16, No.5, 251-257 http://cropscipublisher.com/index.php/mgg 252 2 Physiological Basis and Genetic Characteristics of Stay-Green Trait in Maize 2.1 Definition, classification, and phenotypic evaluation criteria of stay-green trait It is no accident that some corn varieties can still maintain large green leaves during the grain-filling period. This is actually the green retention trait at work - a genetic ability that enables plants to delay leaf senescence and maintain photosynthetic activity after flowering (Hilli, 2021). But "green" can also be genuine or fake. Some only look green on the surface, but in fact, photosynthesis has already stopped. This is called "appearance" greenness preservation. Another type is the "functional" green preservation that can truly continuously synthesize nutrients and stabilize yields (Thomas and Ougham, 2014). Judging these differences cannot rely solely on the naked eye; data is also necessary. For example, green leaf area score (VSG), number of green leaves (GLNM), SPAD values at flowering and maturity (SPADS, SPADM), and green leaf duration (GLAD), etc. These are all commonly used quantitative standards in breeding work (Zheng et al., 2023; 2024). 2.2 Physiological indicators associated with stay-green Whether a variety can "retain its green color" is far from enough to just look at its appearance; it is necessary to delve into its physiological manifestations. High SPAD values often indicate that the chlorophyll is well maintained (Kamal et al., 2019), and if the photosynthesis period is prolonged and dry matter can be continuously produced in the later stage of grout filling, it is basically reliable (Yang et al., 2017; Chibane et al., 2021). However, there are other factors supporting this, such as higher leaf moisture, more active antioxidant enzymes (SOD, POD, CAT), and a good hormone ratio, like higher zeaxanthin and lower abscisic acid (Liu et al., 2018). These indicators, when combined, often determine whether a corn plant can withstand adverse conditions and produce stably. 2.3 Genetic control model of stay-green and overview of reported QTLs In the final analysis, the issue of protecting greenery is still led by genes, but it is not as simple as just one or two genes that control it. This trait is a typical quantitative trait, with both major genes and multiple minor effect genes involved in regulation. Sometimes it also has a slight dominant effect, and the overall heritability is not low (Belicuas et al., 2014). Traits like VSG, GLNM and SPADM can even contribute up to 95% of the major genes in some materials. At present, researchers have identified QTLS related to green conservation on almost all chromosomes of corn. The key regions are concentrated on chromosomes 1, 4, 5 and 6, while chromosome 9 is frequently exposed (Wang et al., 2012). Among them, the gene nac7 encoding the transcription factor of the NAC domain has been confirmed to play a negative regulatory role in senescence. When its expression level is low, the senescence rate of leaves slows down and the yield can be increased (Sekhon et al., 2019; Zhang et al., 2019). With the integration of technologies such as QTL mapping, GWAS and transcriptomics, the genetic structure of green retention traits in corn has become increasingly clear, providing a solid foundation for future molecular marker selection and functional gene discovery. 3 Construction of Near-Isogenic Lines and Phenotypic Evaluation 3.1 NIL development methods and parental selection strategy The establishment process of NIL is not complicated, but it is rather cumbersome to operate. The key lies in whether the loop and selection are combined tightly enough. The general practice is as follows: Repeatedly cross the donor parent with the target QTL (such as green-preserving) and the reincycle parent, and then fix the target fragment step by step through self-crossing combined with molecular markers, while the background genome is as close as possible to the reincycle parent (Zhong et al., 2025). For the parents of reincarnation, materials with good agronomic traits but lacking green retention are often selected, such as common superior varieties like B73. Donor parents, on the other hand, place more emphasis on their performance in the target traits. As for screening markers, molecular markers such as AFLP, SSR, and SNP that are closely linked to green-preserving QTL are sufficient and are most suitable for improving breeding efficiency (Eichten et al., 2011; Ying et al., 2025). 3.2 Phenotypic data collection and statistical analysis under multiple environments The performance of NIL is not consistent in all environments. Whether NIL can "preserve greenery" or not still depends on the performance of multiple environmental tests. The phenotypic data of this type of material usually
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