Molecular Plant Breeding 2024, Vol.15, No.3, 132-143 http://genbreedpublisher.com/index.php/mpb 140 limited genomic information available make it difficult to develop effective markers. This issue is compounded by the diverse genetic backgrounds among breeding material collections, which further complicates the development of a comprehensive linkage map (Moriguchi et al., 2020). 5.1.2 Cost and resource requirements The cost and resource requirements for MAS are significant barriers to its widespread adoption. The process of developing and validating molecular markers, constructing linkage maps, and conducting genotyping is both time-consuming and expensive. For example, the breeding cycle for forest trees can take 20~30 years, making the cost-benefit analysis crucial before implementing genomic selection. Additionally, the need for high-throughput phenotyping methods to complement genotyping efforts adds to the overall resource burden (Lebedev et al., 2020). 5.2 Biological challenges 5.2.1 Genetic complexity of traits The genetic complexity of traits is another major challenge in MAS. Many traits of interest in tree breeding, such as fruit size, weight, and sugar content, are controlled by multiple genes and are influenced by environmental factors. This complexity makes it difficult to identify and utilize molecular markers that can reliably predict these traits. The translation of trait loci and whole-genome sequences into diagnostic genetic markers that are effective and affordable remains a significant hurdle (Mori and Cipriani, 2023). 5.2.2 Gene-environment interactions Gene-environment interactions further complicate the application of MAS in tree breeding. Environmental variability plays a crucial role in the heritability evaluations of important traits, making it challenging to achieve consistent results across different environments. Although vegetative propagation allows for the production of clonal replicates to evaluate environmental effects, the space and labor required for these phenotypic surveys slow down the breeding process (Mori and Cipriani, 2023). 5.3 Socio-economic and regulatory challenges 5.3.1 Acceptance by stakeholders The acceptance of MAS by stakeholders, including breeders, farmers, and regulatory bodies, is a significant socio-economic challenge. There is often skepticism about the reliability and benefits of MAS, particularly when compared to traditional breeding methods. Educating stakeholders about the advantages and potential of MAS is essential for its broader adoption (Kumawat et al., 2020). 5.3.2 Intellectual property issues Intellectual property issues also pose a challenge to the implementation of MAS. The development of molecular markers and the associated technologies often involve significant investment, leading to concerns about patenting and proprietary rights. These issues can create barriers to the sharing of genetic resources and technologies, hindering collaborative efforts in tree breeding (Kumawat et al., 2020). 6 Future Perspectives and Emerging Trends 6.1 Integration of MAS with other biotechnologies 6.1.1 CRISPR and gene editing The integration of Marker-Assisted Selection (MAS) with CRISPR and other gene-editing technologies holds significant promise for the future of tree breeding. CRISPR/Cas9 technology allows for precise modifications at specific genomic locations, which can be used to introduce or enhance desirable traits identified through MAS. This combination can accelerate the breeding process by directly targeting and modifying genes associated with important traits such as disease resistance, growth rate, and wood quality (Degen and Müller, 2023). The convergence of these technologies can potentially overcome the limitations of traditional breeding methods, such as long breeding cycles and complex trait inheritance (Grattapaglia et al., 2018).
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