International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.1, 30-43 http://ecoevopublisher.com/index.php/ijmec 33 showed that the species had high genetic diversity locally (He average value 0.34), and the intra-population variation accounted for 75% of the total variation, indicating that there was still gene exchange between geographically separated populations of yellow-skinned pitaya (Morillo et al., 2022). These studies confirm the importance of global germplasm exchange: the process of introducing and cultivating different regions is itself a process of recombining genetic diversity and expanding the gene pool. Through global introduction and hybridization, breeders are able to integrate the excellent traits of different strains into new cultivated varieties, thereby cultivating new yellow pitaya varieties with higher yield, higher quality and wider adaptability. However, global germplasm flow also brings biosafety risks, such as the risk of pests and diseases spreading with seedlings (Derviş and Özer, 2023). In recent years, the stem blight disease (caused by the fungus Neoscytalidium dimidiatum), which seriously harms pitaya, has broken out in many newly introduced areas and is believed to be related to the transportation of seedlings (Serrato-Diaz and Goenaga, 2021). In this regard, while promoting germplasm exchange, countries need to strengthen quarantine inspection and disease prevention and control research. 4 Genetic Diversity and Its Role in Adaptation 4.1 Types of genetic variation in yellow pitaya populations Genetic diversity is the cornerstone for crops to adapt to different environmental conditions and achieve sustainable development. For yellow pitaya, rich genetic variation enables it to have the potential to grow and bear fruit under different climates and cultivation systems (Morillo et al., 2022). Studies have shown that pitaya germplasm resources are highly diverse at the morphological, cytological and molecular levels. For example, in terms of floral traits, analysis of the floral morphology of pitaya germplasm collected in China found that the flower size, perianth morphology, style length and other indicators of different strains were significantly different, and the Simpson diversity index of floral phenotypes reached 0.22~0.60, indicating that the floral organ characteristics among germplasms are extremely diverse (Huang et al., 2021). At the same time, there is a correlation between floral traits of different germplasms and fruiting ability: the position relationship between stigma and anther, pollen quantity, etc. are significantly correlated with fruit setting rate and fruit size, which are important indicators to pay attention to during breeding. These findings mean that by utilizing the genetic variation of floral traits, it is possible to breed new varieties with large pollen quantity, strong self-pollination ability and excellent fruiting performance. 4.2 Genomic tools for assessing genetic diversity Diversity is also obvious at the genomic level. Korean scholars used simplified genome sequencing to analyze the genetic relationship of 47 pitaya germplasms. The results showed that materials from different sources were clearly clustered into three major groups, corresponding to white flesh, red flesh and yellow skin species. Chinese researchers used flow cytometry to detect the chromosome ploidy of 42 pitaya germplasms and found that there were both diploids and a few natural tetraploids or mixed ploidy conditions, suggesting that pitaya has variation mechanisms such as chromosome doubling. Ploidy variation can lead to changes in plant phenotype and physiology, such as stem fleshiness, fruit size and stress resistance, and therefore has potential application value in breeding. In addition, molecular markers (such as SSR, AFLP, etc.) are used to evaluate the genetic diversity of pitaya germplasm. Okinawa University used 16 newly developed pairs of SSR markers to analyze 32 local pitaya gene pools, and obtained 612 alleles per locus and an expected heterozygosity of 0.500.85, indicating a high level of variation within the genome (Nashima et al., 2021). Most varieties can be distinguished by a small number of core SSR markers, reflecting the effectiveness of marker-assisted identification of germplasm. 4.3 Relationship between genetic diversity and environmental resilience The role of genetic diversity in regional adaptability is mainly reflected in the differences in the response of different genotypes to environmental factors, which makes the species as a whole have a wider ecological range. In pitaya, some varieties are drought-resistant and heat-resistant, and are suitable for fruiting in high temperature and drought environments; others are more resistant to low temperatures or shade and humidity, and can survive in cooler or rainy environments (Lin et al., 2023; Huang et al., 2024). For example, the red-fleshed pitaya variety
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