Genomics and Applied Biology 2024, Vol.15, No.3, 142-152 http://bioscipublisher.com/index.php/gab 145 3 Breeding Strategies inE. ulmoides 3.1 Traditional breeding approaches: limitations and successes The traditional breeding methods for Eucommia ulmoides mainly rely on phenotypic selection and hybrid breeding. These methods have been successful in improving certain traits, such as growth rate and yield. However, they also have significant limitations. Eucommia ulmoides takes seven to eight years to flower from the seedling stage, and it is difficult to distinguish the sex before flowering using morphological or cytological methods, making early identification of superior traits challenging and extending the breeding cycle (Wang et al., 2011). Furthermore, the genetic basis of many important traits remains poorly understood, limiting the effectiveness of traditional selection methods (Li et al., 2014; Jin et al., 2020). Despite these challenges, traditional breeding has laid the foundation for more advanced technologies by providing genetic diversity and heritability of traits, giving us a fundamental understanding of the breeding process. 3.2 Modern breeding techniques: marker-assisted selection, genomic selection Modern breeding techniques have revolutionized traditional Eucommia breeding by integrating molecular markers and genomic data. Marker-assisted selection (MAS) utilizes the close linkage between molecular markers and genes determining target traits. By detecting molecular markers, the presence of the desired gene can be identified, allowing for the selection of target traits. MAS offers advantages such as speed, accuracy, and being unaffected by environmental conditions, making it particularly effective in identifying and selecting quantitative trait loci (QTL) with large effects (Li et al., 2014; Jin et al., 2020). For example, high-density genetic maps developed using single nucleotide polymorphism (SNP) markers have facilitated the identification of QTLs related to growth traits, enabling more precise selection (Liu et al., 2022). Genomic selection (GS) is a new method for breeding selection that uses high-density markers covering the entire genome. It goes a step further than marker-assisted selection by using genome-wide markers to predict an individual's breeding value. This method can capture the effects of all QTLs, including small-effect QTLs, thereby improving selection accuracy (Goddard and Hayes, 2007; Heslot et al., 2015; Merrick et al., 2022). GS has shown outstanding performance in accelerating breeding cycles and increasing genetic gain per unit of time, making it a valuable tool for improving complex traits in Eucommia ulmoides (Varshney et al., 2017). 3.3 Hybrid breeding strategies and their application inE. ulmoides Hybrid breeding strategies combine traditional and modern technologies to maximize genetic gain while controlling inbreeding. One such approach is Mate Selection (MS), which uses optimization algorithms to select the best individuals and their pairings. This method has been shown to reduce inbreeding and increase genetic gain in other species, and it also holds potential for Eucommia ulmoides (Tchounke et al., 2022). The integration of functional markers (FMs) into hybrid breeding strategies can further enhance the precision of selection. FMs are closely associated with phenotypic traits and can be used to directly select for desirable genes, thereby increasing selection efficiency (Salgotra and Stewart, 2020). The use of FMs in combination with MAS and GS can provide a comprehensive approach to breeding E. ulmoides, addressing both the limitations of traditional methods and the complexities of modern genomic techniques. 4 Integrating Functional Genomics into Breeding Programs 4.1 How functional genomics enhances trait selection and breeding efficiency Functional genomics plays a key role in improving trait selection and breeding efficiency by providing detailed insights into the genetic basis of target traits. By identifying and characterizing functional genes, breeders can more efficiently enhance traits such as yield, disease resistance, and stress tolerance through marker-assisted selection (MAS) and genomic selection (GS). For example, the use of functional markers (FMs) allows direct selection of genes associated with phenotypic traits, thus improving selection efficiency and accelerating the breeding of superior varieties. The precision of breeding has greatly improved. Furthermore, advancements in high-throughput sequencing and genome editing have made variety development faster and more precise, further enhancing breeding efficiency (Salgotra and Stewart, 2020).
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