Molecular Plant Breeding 2024, Vol.15, No.5, 259-268 http://genbreedpublisher.com/index.php/mpb 262 5 Integration of MAS in Soybean Breeding Programs 5.1 Workflow of MAS in soybean breeding Marker-Assisted Selection (MAS) integrates molecular genetics with traditional breeding methods to enhance the efficiency and precision of selecting desirable traits in soybean breeding programs. The workflow of MAS typically involves several key steps. The first step is to identify molecular markers linked to traits of interest, such as yield, disease resistance, and stress tolerance. This involves genetic mapping and the use of technologies like Random Amplified Polymorphic DNA (RAPD) markers. Once markers are identified, genotyping is performed on breeding populations to detect the presence of these markers. This step is crucial for selecting individuals that carry the desired traits (Francia et al., 2005; Singh and Singh, 2015). Based on the genotyping results, individuals with favorable marker profiles are selected. This selection can be done at early stages, such as the seedling stage, which saves time and resources (Miedaner and Korzun, 2012; Devi et al., 2017). Selected individuals are then used in hybridization and backcrossing programs to combine desirable traits and develop new cultivars. Marker-assisted backcrossing (MABC) is a common approach used to introgress specific traits into elite lines (Ribaut and Ragot, 2006). The selected lines are validated through field trials across multiple environments to ensure that the desired traits are expressed consistently. This step helps in confirming the effectiveness of MAS in improving traits like yield and stress resistance (Sebastian et al., 2010). 5.2 Examples of MAS breeding programs for yield and stress resistance improvement Several successful MAS breeding programs have been implemented to improve yield and stress resistance in soybeans. A context-specific MAS (CSM) approach was used to detect yield QTL within elite soybean populations. This approach led to statistically significant yield gains of up to 5.8% in selected sublines, with two improved sublines being released as new cultivars (Sebastian et al., 2010). In common bean, MAS was used to identify RAPD markers associated with drought resistance. The selected genotypes showed improved performance under stress conditions, demonstrating the effectiveness of MAS in enhancing drought tolerance. MAS has been successfully applied to select for disease resistance in various crops. For instance, in wheat and barley, MAS has been used to transfer resistance genes for rust, eyespot, and Fusarium head blight into elite breeding material (Miedaner and Korzun, 2012). 5.3 Integration of MAS with traditional breeding methods Integrating MAS with traditional breeding methods offers several advantages. MAS allows for the selection of desirable traits at early stages, reducing the time and resources required for breeding. This is particularly beneficial for traits with low heritability, such as abiotic stress resistance (Singh and Singh, 2015; Devi et al., 2017). MAS provides a more precise selection process by targeting specific genetic markers linked to traits of interest. This reduces the risk of linkage drag and ensures that only the desired traits are selected (Francia et al., 2005). MAS can be combined with traditional phenotypic selection to enhance the overall efficiency of breeding programs. For example, Marker-Assisted Recurrent Selection (MARS) is designed to accumulate favorable QTLs in cross- and self-pollinated crops, complementing traditional selection methods (Singh and Singh, 2015). While the initial costs of genotyping and marker development can be high, the long-term benefits of MAS, such as reduced breeding cycles and improved trait selection, make it a cost-effective approach. 6 Challenges in Implementing MAS in Soybean Breeding 6.1 High costs of marker development and genotyping The implementation of marker-assisted selection (MAS) in soybean breeding is often hindered by the high costs associated with marker development and genotyping. The initial phase of MAS requires scoring genotypes at numerous molecular marker loci, which can be financially demanding. Although advancements in next-generation sequencing (NGS) technologies, such as genotyping-by-sequencing (GBS), have made genotyping more cost-effective, the overall expenses remain significant, especially in the early stages of marker development (He et al., 2014). Additionally, the economic efficiency of MAS compared to traditional phenotypic selection is often questioned due to the high costs of genotyping, which can limit its application to traits with low heritability unless substantial investments are made (Moreau et al., 2000; Kuchel et al., 2005).
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