Plant Gene and Trait 2025, Vol.16, No.4, 182-193 http://genbreedpublisher.com/index.php/pgt 184 The stem of S. undatus is relatively thick, with wavy edges and short triangular thorns. The fruit is oval, with long green scales on the red skin, and white flesh. The edges of the stem segments of S. costaricensis are a bit like saw teeth, the fruit is spherical, the skin is dark red, the scales are short and reddish, and the flesh is purple-red. The stem segments of S. monacanthus are thinner than the previous two, the distance between the thorns is larger, the fruit is oval, the skin is bright red, the scales are short, and the flesh is red. The stem segments of S. megalanthus have small protrusions and short thorns, and the flowers are relatively small and have a yellow tint. Its fruit is yellow and spherical, with obvious protrusions and fine thorns on the outside, and the flesh is white and transparent. Some are new artificially bred varieties, such as Australia’s thornless yellow-skinned pitaya ‘Aussie Gold’. Although it looks like a yellow-skinned pitaya, it is actually a variation of S. undatus. 2.2 Global distribution and preservation of pitaya resources Wild species of pitaya first appeared in tropical areas of Central and South America, such as Mexico, Central America, and some countries in northern South America (Morillo et al., 2022). Now, many countries’ planting areas and scientific research institutions have collected and preserved pitaya germplasm resources. In Mexico, national universities and other institutions have established germplasm nurseries, collecting local strains of H. undatus from multiple places and some wild Selenicereus species (Hernández-Andrade et al., 2019). Colombia has also collected its own yellow-skinned pitaya (S. megalanthus), which are mainly used for genetic research and breeding. Vietnam is the country with the largest export of pitaya. They have established national germplasm nurseries in Long An Province and other places, preserving the country’s main varieties, such as the white-fleshed ‘Pingshun Longan’, and have also introduced red-fleshed varieties from Thailand for hybrid breeding (Xu and Wang, 2024). In China, germplasm repositories have been established in provinces such as Guangdong, Guangxi, and Hainan. Institutions like South China Agricultural University and Guangxi Academy of Agricultural Sciences have collected many white-, red-, and hybrid-fleshed varieties from Vietnam, Taiwan, and Hainan. Hainan University focuses on conserving the main cultivated types in China and currently maintains close to 100 accessions. Additionally, Ben-Gurion University in Israel has developed a large living germplasm collection with over 200 pitaya accessions introduced from various countries. 2.3 Diversity of main agronomic traits of pitaya In terms of fruit, different varieties have different fruit sizes and shapes. Some fruits weigh only a few dozen grams, while some large ones can exceed 500 grams (Abirami et al., 2021). For example, the yellow-skinned species (S. megalanthus) are usually small, generally less than 150 grams. Some red-fleshed varieties, such as ‘Okan’ cultivated in Israel, can weigh more than 500 grams per fruit. The peel color is red and yellow, and the scales on the peel are long or short, and the color may also be green or red (Li et al. 2024). The flesh color also varies, including white, red, purple-red, and some are pink intermediate colors. Different varieties have different sweetness and taste, and red flesh is usually sweeter than white flesh. For example, among the three types of pitaya grown in the Andaman Islands of India, the red flesh variety has the highest sugar content and the most antioxidants. The nutrients in the pulp, such as vitamin C, anthocyanins, dietary fiber, etc., also vary among different varieties (Shah et al., 2023). Plant architecture and flowering/fruiting traits also vary. Some cultivars branch more, others less. Flower sizes vary. Certain white-fleshed types are self-incompatible and require cross-pollination. However, newly bred varieties in China, such as ‘Guibao’ and ‘Baiyu Jing’, are self-compatible. Spines on cladodes differ too-some varieties are almost spineless, while others have 3~5 long spines. In terms of stress resistance, different pitayas respond differently to pests and diseases and bad weather. Some wild varieties, such as S. setaceus, are more drought-tolerant and disease-resistant, but the fruit is smaller. Red-fleshed cultivars are generally more resistant to transportation than white-fleshed ones, but do not perform as well as white-fleshed ones in cold weather (Zhou et al., 2020). Some varieties can activate protective mechanisms, such as “autophagy”, after the branches are cold-treated, which can reduce chilling damage (Zhou et al., 2021). Some varieties are more susceptible to blight or anthracnose after picking, but some show better disease resistance (Balendres and Bengoa, 2019; Yao et al., 2022).
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