Plant Gene and Trait 2025, Vol.16, No.4, 182-193 http://genbreedpublisher.com/index.php/pgt 186 are often divided into one group and red flesh varieties are divided into another group. This may be because many red-fleshed varieties come from the same breeding material, such as having a common parent, while white-fleshed varieties may be traditional strains. However, there are exceptions, such as some white-fleshed varieties in Taiwan and Vietnam, which are mixed with red-fleshed varieties in SSR cluster analysis. This may be because these white-fleshed varieties are mixed with genes of red-fleshed varieties during breeding. Some newly bred self-compatible varieties in southern China are mostly selected from the offspring of the varieties introduced by ‘Vietnamese White’ (Nashima et al., 2021). The hybrid offspring bred with the Brazilian wild species H. setaceus as the father are very different from the general cultivated varieties in appearance and genetic analysis (Li et al., 2024). 4 Application Value of Pitaya Genetic Diversity in Breeding 4.1 Parent selection strategy guided by diversity information In traditional breeding, we often encounter a problem: good varieties are too similar, and the hybrid offspring do not change much. In order to make the offspring more different, breeding experts now use a method called “molecular markers” to look at the genetic differences between different materials. In this way, varieties with relatively far different genes can be selected as parents. Because many commercial varieties are developed from several old varieties, if the parents are too close, the genes of the offspring may be more single. Some studies have used tools like SSR to analyze this. They found that when two varieties fall into different branches on a “clustering tree,” they likely have more genetic differences and are better for crossbreeding. Some researchers in China have used molecular markers to perform cluster analysis. They found that some red-fleshed strains that can bear fruit on their own are quite different from traditional white-fleshed strains. Such red-fleshed strains can be paired with white-fleshed strains, so that the new generation may have the advantages of “self-flowering” and “high-sugar red meat” (Li et al., 2024). In Vietnam, local breeders hybridized a local white-fleshed strain with red-fleshed materials introduced from Colombia. In the end, a new red-fleshed strain, Longding No.1, was obtained, which can also bear fruit on its own (Mitra, 2024). It is also not good if the selected parents are too closely related. In Israel, breeders created a large database of over 200 dragon fruit accessions with “molecular fingerprints”. Before pairing the parents, they can check whether they are too closely related. 4.2 Integration of excellent trait-related markers and breeding utilization Through a variety of genetic diversity analyses, researchers have found gene markers related to some important traits of pitaya (such as flesh color, sweetness, and self-compatibility). For example, using the transcriptome comparison method, a glycosyltransferase gene that is only expressed in red-fleshed pitaya was found, and a molecular marker was developed based on this. This marker can help us distinguish between red-fleshed and white-fleshed varieties (Figure 2) (Le Bellec et al., 2006; Mou et al., 2022). Self-incompatibility of pitaya has always been a breeding problem. In recent years, some studies have found some key genes related to self-compatibility. Wang et al. (2023) compared the expression of styles of compatible and incompatible varieties and found several candidate genes with higher expression levels in incompatible varieties, such as S-RNase and F-box genes. Molecular markers for S-RNase have been developed, which can be used to determine whether a variety is self-compatible. During breeding, plants with certain mutations that cause self-compatibility (such as loss of function) can be selected through these markers. Some dragon fruit varieties are also resistant to stem blight, and related RAPD molecular markers have also been found. In a breeding program in Hainan, researchers used high-density SNP molecular markers to establish a genetic map. They used this map to locate QTLs in an F1 population and found several important loci related to fruit sweetness. Then, they used molecular markers to select individual plants with excellent genes for self-pollination and offspring selection. As more functional molecular markers were discovered, such as the HpDof1.7 and 5.4 markers that regulate sugar accumulation, there are also markers related to flowering time.
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