Plant Gene and Trait 2025, Vol.16, No.4, 182-193 http://genbreedpublisher.com/index.php/pgt 189 genetic maps to find QTLs linked to sweetness (Figure 3) (Chen et al., 2021). Based on this, they developed SNP markers to identify seedlings with favorable sweetness genes in F1 populations. After two generations of selection, the average sugar content of new varieties increased by about 2 Brix. Figure 3 Genes involved in the betalain biosynthesis cascade (Adopted from Chen et al., 2021) Image caption: A The development of ‘Guanhuabai’ (GHB) and ‘Guanhuahong’ (GHH) pitaya pulp. B The betacyanin and betaxanthin contents of ‘GHB’ and ‘GHH’ pitaya pulp. C The expression profiles of genes related to betalain biosynthesis according to the RNA-Seq datasets of ‘GHB’ and ‘GHH’ pitaya pulp. The gene IDs are in brackets. Spon, spontaneous. Bar = 2 cm (Adopted from Chen et al., 2021) The team also used SSR fingerprinting technology to confirm whether the hybridization was successful. For example, when doing a “three-line” hybridization experiment, they used SSR molecular markers to confirm whether the hybrid offspring came from the predetermined parents, and promptly eliminated those self-pollinated seedlings or hybrid seedlings. The results show that molecular marker technology is indeed very useful in pitaya breeding (Shah et al., 2023). At present, they have used this method to breed several new varieties, such as ‘Zixialong’ and ‘Xinghui No.1’. These varieties have performed well and have entered the stage of regional trials and promotion of planting. 5.3 Hybrid germplasm innovation using wild dragon fruit from Mexico In Mexico, breeders used local wild dragon fruit species to develop new varieties. Their goal was to introduce wild traits into cultivated types. Since the late 1990s, a team from the National University of Mexico collected local wild relatives of dragon fruit. These included species from Hylocereus (also known as Selenicereus) and other edible cacti. One special wild type, Hylocereus purpusii, has rare orange-yellow flesh and a strong aroma. However, its fruit is small and its vines are hard to manage. Researchers crossed H. purpusii with a cultivated red-flesh variety (Hernández-Andrade et al., 2019). They used embryo rescue to produce the first-generation hybrids. These hybrids had larger fruit than the wild type, with orange-red flesh and good flavor. After more backcrossing and selection, they created lines with fruit sizes close to commercial types but retained the orange color and aroma. One of these is named ‘Xíitek’, meaning “rainbow”
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