Plant Gene and Trait 2025, Vol.16, No.1, 15-22 http://genbreedpublisher.com/index.php/pgt 16 2 Foundation of Superior Trait Selection inSapindus 2.1 Theoretical basis and current research on trait selection inSapindus Recent studies have found that there are significant genetic differences in the populations of Sapindus mukorossi in different regions. Chung and Liao (2022) completed the chromosome-level genomic assembly of Sapindus and identified many genes related to defense, growth, and development. Silva et al. (2021) also discovered the relationship between fruit traits and certain molecular markers through their research using ISSR molecular markers. These results provide an important genetic basis for trait screening. 2.2 Selection criteria for phenotypic traits and their relationship to application value The external properties of Sapindus and its application value, especially in the production of vegetable oils and chemicals, are closely related. Liu et al. (2021) established a comprehensive evaluation system in order to select high-quality Sapindus tree species, focusing on key traits such as oil content, seed size and biomass. This system uses a method called “projection tracing” to determine how important each trait is, ensuring that the screening process is scientific and comprehensive. In 2018(b), Sun et al. also screened the germplasm resources of Sapindus based on agronomic traits and identified several superior varieties with relatively high contents of oil and saponins, which is of great value for the development of biodiesel and green chemical products. 2.3 Field trials and methods for phenotypic data collection and analysis Xue et al. (2022) evaluated 25 traits in the Sapindus seedling population and used phenotypic variation analysis, principal component analysis (PCA), and correlation analysis to examine the extent of the differences among these traits. This method is beneficial for identifying which traits are most suitable for judging the diversity of Sapindus, thereby screening out superior individuals more quickly. Another study evaluated different Sapindus varieties using 19 agronomic traits. The results showed significant differences in yield and economic traits among them, providing useful data support for finding high-yielding and stable good varieties. 3 Role of Molecular Markers inSapindus Breeding 3.1 Overview of molecular marker technologies and their application in plant breeding There are many commonly used types of markers nowadays, such as ISSR and EST-SSR. These methods are widely used in the genetic research of Sapindus. The ISSR technology can be used to analyze the genetic diversity of Sapindus and identify molecular markers related to fruit traits, which is very useful for breeding efforts to improve fruit quality and oil yield. EST-SSR can be used to study population structure and help establish the core germplasm resources of Sapindus, which is very important for resource management and conservation (Fu et al., 2017). Benchimol-Reis (2023) indicates that these markers are increasingly widely used in breeding with the development of sequencing technology. New markers are constantly being developed, and marker-assisted selection (MAS) has also become easier to be applied in actual breeding. 3.2 Development and validation of markers related to target traits inSapindus The key to developing molecular markers related to the target traits of Sapindus is to identify those gene loci related to seed oil, saponin content in fruits, fruit quality, etc. The study by Yang et al. (2015) used ISSR labeling technology to identify 18 loci related to 13 fruit traits, including seed oil and saponin yields. They can help breeders select the desired traits more quickly and accurately. Schulman (2007) confirmed through association analysis in his early studies that there were indeed associations between these markers and the target traits, ensuring the reliability of these markers. Once these markers are successfully verified, they can be directly applied to the breeding program to enhance the superior traits of Sapindus. 3.3 Experimental evidence for the correlation between molecular markers and target traits The study by Liu et al. (2022) used ISSR markers in Sapindus mukorossi and S. delavayi and found that some gene loci were significantly associated with traits such as seed oil and saponins. These results were also supported by EST-SSR marker analysis, which revealed the genetic differences and structures of these Sapindus populations. This information is very useful for breeding work. Verifying the relationship between these markers and traits is the key to making marker-assisted breeding (MAS) truly effective. Only when it is confirmed that these markers can accurately predict traits can they play a guiding role in breeding (Figure 1) (Fu et al., 2017).
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