Tree Genetics and Molecular Breeding 2025, Vol.15, No.5, 211-219 http://genbreedpublisher.com/index.php/tgmb 216 7 Case Study: Breeding and Field Application of Stress-Tolerant M. glyptostroboides 7.1 Research background and breeding objectives Metasequoia glyptostroboides is a rare relict tree species with strong adaptability and high ecological value. It is often used for ecological restoration and landscaping. However, it is prone to stress in drought and saline-alkali environments, so enhancing its stress resistance has become an important goal in breeding. The current research focus is on utilizing the genetic diversity of Metasequoia glyptostroboides to select and breed superior strains with better stress resistance for ecological restoration and sustainable utilization (Li et al., 2018; Kong et al., 2022; Li et al., 2025a). 7.2 Methods: germplasm evaluation, molecular tools, and field trials The stress-resistant breeding of Metasequoia glyptostroboides has adopted a variety of methods. Li et al. (2025a) evaluated the genetic diversity of the introduced population by using multi-site SSR molecular markers. These data reveal the richness and population structure of germplasm resources, providing a reference for breeding. An efficient tissue culture and micropropagation system was established to rapidly propagate superior genotypes, solving the problem of low propagation efficiency of traditional methods (Xiong et al., 2019). In terms of enhancing stress resistance, Li et al. (2018) and Kong et al. (2022) also combined field and greenhouse experiments to test different treatment methods, such as inoculating growing-promoting bacteria and adding superabsorbent polymers, to observe their effects on the growth and physiological indicators of seedlings. Through root anatomy and physiological analysis, it was also found that Metasequoia glyptostroboides could show obvious phenotypic plasticity between the aquatic and terrestrial environments, providing an anatomical basis for studying its stress resistance mechanism (Yang et al., 2019). 7.3 Outcomes: improved lines, ecological benefits, and practical adoption These methods have screened out many excellent drought-resistant and salt-tolerant varieties. In field applications, inoculation of growth promotive bacteria or addition of polymers can significantly increase the growth amount of seedlings, enhance the photosynthetic capacity of leaves and the activity of antioxidant enzymes, and also reduce the ionic toxicity caused by salt stress, thereby improving overall stress resistance (Li et al., 2018; Kong et al., 2022). The establishment of the micropropagation system has also enabled the large-scale promotion of superior strains, providing reliable seedlings for ecological restoration projects (Xiong et al., 2019). In practical restoration applications, these Metasequoia glyptostroboides have improved soil structure, increased vegetation coverage and ecosystem stability, and brought about good ecological and social benefits (Li et al., 2018; Kong et al., 2022; Li et al., 2025a). 8 Challenges and Limitations 8.1 Long lifecycle and delayed breeding outcomes Metasequoia glyptostroboides is a long-lived tree with a long life cycle and a slow alternation of generations. This has led to very slow progress in the selection and breeding of new varieties and the improvement of their traits under traditional breeding methods. It often takes a long time from hybridization to stable traits, and thus it is difficult to respond quickly to environmental changes and adverse stress (Xiong et al., 2019; Li et al., 2025a). 8.2 Technical gaps in transformation and genome editing for woody species At present, Metasequoia glyptostroboides and other woody plants all face many challenges in genetic transformation and gene editing. The efficient genetic transformation system is still not mature, the efficiency of gene editing is low, and the tissue culture and regeneration system is also unstable. These problems have severely restricted the progress of molecular breeding and precision improvement (Xiong et al., 2019). Although some breakthroughs have been made in in vitro rapid propagation technology, the genetic manipulation of woody plants is still more difficult compared with herbaceous crops. 8.3 Need for wider genetic resource exploration and international collaboration The natural distribution range of Metasequoia glyptostroboides is very small, its genetic basis is relatively limited, and the diversity of existing breeding materials is insufficient. Although introduction and artificial cultivation have expanded the population distribution, the genetic differentiation among populations is not significant, and
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