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Abstract―This study explored the morphological characteristics and effects of pollination methods on fruit set and characteristics in

4 red pitaya (Hylocereus spp.

) clones. The distinctive morphological recognition and classification among pitaya clones were confirmed by the stem, flower and fruit features. The fruit production season was indicated from the beginning of May to the end of August C the beginning of September with 6-7 flowering cycles per year. The floral stage took from 15-19 days and fruit duration spent 30C32 days. VN White, fully self-compatible, obtained high fruit set rates (80.0C90.5%) in all pollination treatments and the maximum fruit weight (402.6g) in hand self- and (403.4g) in open-pollination. Chaozhou

5 was partially self-compatible while Orejona and F11 were completely self-incompatible. Hand cross-pollination increased significantly fruit set (95.8;

88.4 and 90.2%) and fruit weight (374.2;

281.8 and 416.3 g) in Chaozhou 5, Orejona, and F11, respectively. TSS contents were not much influenced by pollination methods. Keywords―Hylocereus spp., morphology, floral phenology, pollination requirement. I. INTRODUCTION ITAYA or dragon fuit (Hylocereus spp.) originated from the Americas [1] with a wide distribution in tropical and subtropical regions [10], [11]. It is increasingly gaining interest in many countries, including Taiwan due to their high economic potential as exotic fruit crops and their exceptional tolerance to extreme drought [11], [13], [15]. The benefits of dragon fruit for human health could be explained by its essential nutrients such as vitamins, minerals, complex carbohydrates, dietary fibres and antioxidants [7]. Pitaya cultivars being grown on commercial scale belong to four species: H. undatus, H. monacanthus (syn. H. polyrhizus), H. costaricensis and Selenicereus megalanthus (syn.) H. megalanthus, and their hybrids. [8], [14], [17], [18], [20]. There is great disagreement about specific circumscriptions in the genus. This is due, in part, to the fact that most species of Hylocereus were similar in stem and flower morphology. The main differences among several Hylocereus species were the size and color of the fruit, and the number and form of the spines [3]. The separation of species and varieties in the genus Hylocereus was difficult due to the high intra- and interspecific hybridization [17], which has caused some taxonomic confusion. Therefore, currently, in order to recognition and evaluation of new piatya varieties, Dinh Ha, Tran is with Department of Plant Industry, National Pingtung University of Science and Technology, Pingtung 921, Taiwan (Corresponding author, phone : +886-934-155-059, e-mail: [email protected]). Chung C Ruey Yen is with Department of Plant Industry, National Pingtung University of Science and Technology, Pingtung 921, Taiwan. International Union for the Protection of New Varieties of Plants (UPOV) proposed The Guidelines for the Conduct of tests for Distinctness, Uniformity and Stability (DUS) applying to Dragon fruit (Hylocereus undatus (Haw.) [6]. This document standardized and described the fully characteristics of pitaya as the stem, flower and fruit. Regarding the reproductive biology, most studies reported that it had large, hermaphroditic nocturnal ?owers, and belonged to the long day plant with natural flowering and production during warmer months [10], [11]. In Israel H. polyrhizus and H. costaricensis were indicated as self- incompatible (SI), requiring cross-pollination to set fruit while H. undatus and S. megalanthus were self-compatible (SC), setting fruit with self-pollination [12], [20]. In contrast with findings of [20], in the natural habitat in Mexico H. undatus had the highest fruit set both open and unmanipulated self- pollination [19];