International Journal of Horticulture, 2024, Vol.14, No.6, 414-425 http://hortherbpublisher.com/index.php/ijh 418 3.4 Gene editing technology Gene editing technologies, particularly CRISPR/Cas9, have opened new avenues for the precise modification of key genes in dragon fruit to achieve desired traits. CRISPR/Cas9 allows for targeted modifications at specific genomic loci, enabling the precise editing of genes involved in important traits such as disease resistance, fruit quality, and stress tolerance (He et al., 2017; Chen et al., 2021). This technology has the potential to overcome the limitations of traditional breeding methods by directly altering the genetic makeup of dragon fruit, thereby accelerating the development of improved varieties. The application of CRISPR/Cas9 in dragon fruit breeding is still in its early stages, but it holds great promise for the future of varietal improvement. An example of the application of CRISPR/Cas9 in dragon fruit breeding is the targeting of genes involved in sugar synthesis to enhance fruit flavor. By precisely editing genes that regulate sugar metabolism, researchers can increase the sugar content of dragon fruit, resulting in sweeter and more flavorful fruits (Chen et al., 2021). This approach not only improves the sensory qualities of dragon fruit but also enhances its marketability and consumer appeal. The successful application of CRISPR/Cas9 in modifying sugar synthesis genes in dragon fruit demonstrates the potential of gene editing technologies to achieve specific breeding goals with high precision and efficiency. 4 Advances in Varietal Improvement of Dragon Fruit 4.1 Genetic diversity of dragon fruit varieties Dragon fruit (Pitaya) exhibits significant genetic diversity, particularly among its different varieties, which include red-skinned white-fleshed, red-skinned red-fleshed, and yellow-skinned white-fleshed types. Studies have shown that red-fleshed varieties generally have higher antioxidant capacities and total phenolic content compared to white-fleshed varieties (Attar et al., 2022). Additionally, metabolomic analyses have revealed that red-skinned cultivars with different pulp colors (red, pink, and white) exhibit distinct primary metabolite profiles, including variations in glucose, fructose, and sucrose levels during fruit maturation (Hua et al., 2018). Genetic diversity studies using SSR markers have identified significant genetic variation among different germplasm accessions, indicating a rich genetic pool that can be utilized for breeding programs (Pan et al., 2017). 4.2 Primary goals in varietal improvement The primary goals in the varietal improvement of dragon fruit include enhancing fruit quality, extending shelf life, and improving disease resistance and stress tolerance. Enhancing fruit quality involves improving texture and sweetness, which are critical for consumer acceptance. For instance, cultivars such as N97-20 and NOI-13 have been noted for their higher individual fruit weight and soluble solids content, which are indicators of better fruit quality (Goenaga et al., 2020). Extending shelf life and improving disease resistance are also crucial, as these factors directly impact the commercial viability of the fruit. Genetic studies have identified genes related to drought stress and hormone-mediated signaling pathways, which could be targeted to develop more resilient varieties (Oltehua-Lopez et al., 2023). 4.3 Application of genetic improvement techniques Various genetic improvement techniques have been employed to enhance dragon fruit varieties. Traditional breeding methods, such as hybrid breeding and interspecific crosses, have been used to produce improved hybrids with desirable traits (Tel-Zur, 2022). Marker-assisted selection (MAS) has also been utilized to identify and select for specific genetic markers associated with beneficial traits. Modern techniques like gene editing are being explored to precisely modify genes involved in key pathways, such as betalain biosynthesis, which is responsible for the red coloration in some dragon fruit varieties (Xi et al., 2019; Chen et al., 2021). Transcriptome analyses have further clarified the genetic mechanisms behind traits like flesh coloration, providing valuable insights for targeted breeding (Fan et al., 2020). 4.4 Successful cases Several newly developed superior dragon fruit varieties have shown promising performance in production. For example, cultivars N97-17, N97-20, N97-22, and NOI-13 have demonstrated significantly higher fruit yields and
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