International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.1, 30-43 http://ecoevopublisher.com/index.php/ijmec 34 ‘Dahong’ has strong resistance to high temperatures and sunburn, and is suitable for open-field cultivation in the tropics; while the white-fleshed variety ‘Vietnam White’ is relatively shade-tolerant and can bloom and bear fruit normally under weak light conditions in the greenhouse, so it is often used in facility cultivation. Another example is that yellow-skinned pitaya germplasm is generally sensitive to soil drought, but some materials from the Andes region have better tolerance to low temperatures than ordinary varieties, which provides material for improving the cold resistance of pitaya. A study compared the metabolite differences between red-fleshed pitaya and white-fleshed pitaya and found that the red-fleshed type accumulated more pigment secondary metabolites such as betacyanin, which may be related to its antioxidant and UV resistance, while the white-fleshed type is more active in certain carbohydrate metabolic pathways (Lin et al., 2021). These differences are all manifestations of genetic diversity, reflecting the specific adaptive characteristics formed by different strains under long-term natural selection or artificial selection. It is worth mentioning that self-incompatibility is also an aspect of the genetic characteristics of pitaya. Some red-fleshed pitaya varieties have difficulty in self-pollination and must be cross-pollinated to ensure yield. However, through multiple generations of artificial selection, some self-compatible strains (such as the red-fleshed strain introduced from Vietnam) have been bred. The genetic control of self-incompatibility involves multiple loci, and the accumulation of corresponding variations has led to different types of pitaya in this important reproductive trait, providing convenient self-pollinating varieties for production. This shows that genetic variation makes it possible for pitaya to adapt to different cultivation modes (artificial pollination or natural fruiting). 5 Mesoamerican Regional Adaptation Mechanism 5.1 Climatic factors influencing local adaptation The tropical environment of Central America, where the yellow pitaya originated, has shaped its unique physiological and ecological adaptation mechanism. The typical ecological characteristics of the origin are high temperature, seasonal drought and strong light, which have enabled the dragon fruit plants to evolve a series of adaptive strategies to survive and reproduce in adversity. Yellow pitaya has fleshy stems and crassulacean acid metabolism (CAM) photosynthesis mechanism, which is an important physiological basis for drought adaptation. The fleshy stem is rich in mucilage, which can store water in the tissue and maintain water balance under drought conditions (Lee and Chang, 2024). CAM photosynthesis absorbs CO2 by opening stomata at night and closing stomata during the day to reduce transpiration, thereby reducing water loss during hot and dry days. Studies have confirmed that pitaya is a typical non-facultative CAM plant, which mainly uses the CAM pathway to fix carbon regardless of sufficient water supply or drought stress (Wang et al., 2019). This mechanism enables it to survive in arid environments with an annual rainfall of only 350 mm (Shah et al., 2023). However, persistent severe droughts still interfere with pitaya photosynthesis, reducing the net CO₂ absorption rate. This may be related to drought-induced chlorophyll oxidation damage and destruction of photosynthetic machinery. But in general, thanks to CAM metabolism, yellow pitaya is more tolerant to water deficit than C₃ and C₄ plants, and its biomass produced per unit water consumption is higher, and it is considered to be a crop with high water use efficiency. Pitaya native to Central America often grows on tree crowns or climbing rocks, and relies on CAM metabolism to survive in high temperature and exposure environments. This adaptation continues to work when introduced to areas with similar dry and hot climates (such as the Mediterranean coast). 5.2 Genotype-by-environment interaction in yellow pitaya Yellow pitaya has low requirements for soil and nutrient conditions and shows characteristics of adapting to poor soils. In its native habitat, pitaya is commonly found in sandy soil or limestone areas with low humus content, and obtains limited nutrients through a well-developed root system and symbiotic microorganisms (Gong et al., 2024). Studies have isolated endophytic strains with phosphorus solubilization, potassium solubilization and nitrogen fixation functions from the rhizosphere of pitaya, such as Trichoderma and Bacillus, which can increase the effective phosphorus and potassium content in the soil and promote the growth of pitaya plants. This shows that pitaya may rely on rhizosphere growth-promoting bacteria to provide nutrients and improve its adaptability in a
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