Plant Gene and Traits 2024, Vol.15, No.4, 207-219 http://genbreedpublisher.com/index.php/pgt 210 4 Molecular Markers and Marker-Assisted Selection (MAS) 4.1 Identification of molecular markers linked to key traits inCamellia The identification of molecular markers linked to key traits in Camellia has been a significant advancement in plant breeding. Molecular markers such as single nucleotide polymorphisms (SNPs) and expressed sequence tag-simple sequence repeats (EST-SSRs) have been effectively utilized to identify associations with traits of interest. For instance, a functional molecular marker, EST-SSR073, has been identified for detecting blister blight disease resistance in tea (Camellia sinensis), marking a milestone in tea molecular breeding (Karunarathna et al., 2020). The development of these markers involves genotyping populations and performing linkage analysis to associate specific markers with phenotypic traits. 4.2 Application of MAS in improving traits like oil content, tea quality, and stress tolerance Marker-assisted selection (MAS) has been applied to improve various traits in Camellia, including oil content, tea quality, and stress tolerance. MAS allows for the selection of desirable traits at the seedling stage, thus saving time and resources (Devi et al., 2017). For example, MAS has been used to enhance stress tolerance by selecting for traits related to abiotic stress resistance, which is crucial given the challenges posed by climate change. Additionally, MAS has been employed to improve tea quality by selecting for traits such as disease resistance and nutrient efficiency, which directly impact the quality of the final product (Hasan et al., 2021). 4.3 Success stories of MAS inCamellia breeding programs There have been several success stories of MAS in Camellia breeding programs. One notable example is the use of the EST-SSR073 marker for breeding blister blight-resistant tea cultivars, which has significantly reduced crop losses due to this fungal disease (Karunarathna et al., 2020). Another success story involves the application of genotyping-by-sequencing (GBS) and amplicon sequencing (AmpSeq) technologies, which have streamlined the process of marker discovery and genotyping, thereby accelerating the breeding of stress-tolerant and high-quality Camellia varieties (Yang et al., 2016). These advancements have demonstrated the potential of MAS to revolutionize Camellia breeding by increasing the precision and efficiency of selecting superior genotypes. 5 QTL Mapping and Association Studies inCamellia 5.1 Overview of quantitative trait loci (QTL) mapping inCamellia Quantitative trait loci (QTL) mapping is a powerful tool used to identify the genetic basis of complex traits in plants. This method involves linking phenotypic data (observable traits) with genotypic data (genetic markers) to locate regions of the genome that contribute to variation in these traits. Traditional QTL mapping relies on biparental populations, which are derived from crossing two genetically distinct parents. This approach has been successfully applied in various crops to identify loci associated with important agronomic traits (Pascual et al., 2016). 5.2 Application of genome-wide association studies (GWAS) to identify loci related to important traits Genome-wide association studies (GWAS) have emerged as a complementary approach to traditional QTL mapping. Unlike biparental QTL mapping, GWAS utilizes natural populations with diverse genetic backgrounds, leveraging historical recombination events to achieve higher resolution in identifying loci associated with traits of interest. GWAS has been effectively used in crops like tomato, soybean, and rice to identify QTLs for traits such as fruit quality, yield, and stress tolerance (Kim et al., 2021). In Camellia, GWAS can be particularly useful for identifying loci related to traits such as flower color, oil content, and disease resistance. By analyzing a diverse collection of Camellia accessions, researchers can uncover marker-trait associations that are valuable for breeding programs. For instance, a study on soybean demonstrated the utility of integrating GWAS with genotyping-by-sequencing (GBS) to provide dense genome-wide marker coverage, leading to the identification of significant loci for various agronomic traits. 5.3 Challenges and opportunities in using QTL mapping for Camellia improvement While QTL mapping and GWAS offer significant potential for Camellia improvement, several challenges must be addressed. One major challenge is the reproducibility of results across different environments and populations. The transferability of QTLs identified in one population to another can be limited due to differences in genetic
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