Plant Gene and Trait 2025, Vol.16, No.4, 182-193 http://genbreedpublisher.com/index.php/pgt 188 anthocyanin content, which is good for health. Crossing it with Hylocereus dragon fruit may improve taste and nutrition. Although intergeneric hybridization between Selenicereus and Stenocereus is still difficult, some unique hybrid markers have been detected in a few seedlings. 4.4 Potential for whole-genome breeding and precision selection Breeding has now entered the genomics era. New technologies such as genome-wide selection (GS) and gene editing are already used in fruit tree breeding. Chen et al. (2021) sequenced the genome of a variety called ‘Guangzhou White’ and found it has a genome size of 1.41 Gb, with 27 753 annotated genes. Comparative analysis showed that dragon fruit has undergone triploidization and gene duplication, and some gene families have expanded. These changes are related to traits like fruit color (Zheng et al., 2021). Researchers also used resequencing to build a high-density genetic map of dragon fruit and tried genome-wide association studies (GWAS). Wu et al. (2021) analyzed 109 F1 individuals and found candidate markers related to fruit length, diameter, sweetness, and other traits. Because dragon fruit takes two to three years from seed to fruit, the breeding cycle is long. GS technology may help shorten this time significantly. In gene editing, several genes affecting fruit redness (such as CYP76AD1, DODA, and ADH) have been found to differ across varieties. 5 Case Studies 5.1 Vietnam’s national germplasm bank and breeding with high diversity parents In Binh Thuan Province in southern Vietnam, there is a national dragon fruit germplasm bank. It holds many types of dragon fruit, including local white-fleshed varieties, red-fleshed ones introduced from Central America, and a few yellow-skinned types (Mitra, 2024). Researchers analyzed these and found many differences in their traits. The traditional white-fleshed variety ‘Binh Thuan’ has high yield and good disease resistance, but the pale flesh color is less attractive. The red-fleshed variety from Colombia has bright color, but its fruit set rate in Vietnam is very low. To combine the strengths of both, breeders at the Long An Agricultural Research Center did a hybridization experiment. They used 'Binh Thuan' as the female parent and crossed it with the red-fleshed line with good color but poor self-pollination. After several rounds of selection, they developed a new red-fleshed variety named ‘Long Định 1’. ‘Long Định 1’ keeps the high yield and adaptability of 'Binh Thuan’, has red-purple flesh, and is very sweet. Most importantly, it can self-pollinate, solving the problem of poor fruit set in red-fleshed varieties. Genetic tests also confirmed that it inherited key genes from both parents based on SSR marker analysis (https://www.kingelong.com.vn/blogs/market-news/why-do-red-dragon-fruits-intended-to-be-exported-to-japan-h ave-to-be-s). This new variety is now widely grown in Vietnam. It is well accepted because it sets fruit easily and has good quality. Besides this, Vietnam also tried other crosses, like combining Thailand’s self-pollinating red-flesh types with local varieties. One result is the ‘Dragon Pearl’ series, which also performs well. 5.2 Molecular marker-assisted breeding case of Hainan research team in China The research team of the College of Tropical Agriculture of Hainan University established a germplasm resource garden, which collected the main varieties planted in China and some introduced germplasms. They used molecular markers to analyze the genetic diversity of these materials and screened out core germplasms (Li et al., 2024). The team focused on several important traits and carried out molecular marker-assisted breeding. White meat varieties usually require artificial pollination, which is not very convenient. To solve this problem, the Hainan team introduced self-fertile varieties from Israel, used them as parents, and hybridized with local high-yield white meat varieties to obtain a batch of offspring. In order to improve the screening efficiency, they used the previously developed S-RNase molecular marker technology to detect whether these seedlings carry self-compatible genes (Wang et al., 2023). In this way, plants that cannot self-fertilize can be eliminated at the seedling stage, leaving single plants that may be self-fertile to be verified in the field. Finally, the new varieties bred, such as ‘Bai Yulong’, can produce stable fruits without artificial pollination. They also used high-density
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