Regulation of floral bud development and emergence by ambient temperature under a long-day photoperiod in white-fleshed pitaya (Hylocereus undatus)
Graphical abstract
The schematic flow of bud development and emergence regulated by ambient temperature in white-fleshed pitaya. Warm temperatures (32/22 °C day/night temperature) enhanced dormant bud development, and stimulated reproductive bud emergence within 3–4 weeks. The experimental modification of ambient temperature, 29/19 °C forced reproductive bud emergence in nine weeks and may be the minimum required temperature for flowering. Lower temperatures repressed bud development, resulting in most buds remaining in a vegetative state. These results demonstrate an important role for temperature in flowering in white-fleshed pitaya, which may have implications for off-season production processes.
Introduction
Pitaya (Hylocereus spp.) is a climbing cactus crop that is grown globally, but especially in Southeast Asian countries (Hoa et al., 2015; Mizrahi et al., 1997; Zee et al., 2004), with the red-fleshed (Hylocereus sp.) and white-fleshed (H. undatus) varieties having become the most widely grown in recent decades. Improvements in the commercial production of pitaya (Jiang and Yang, 2015a) have led to increased production in Taiwan, where this crop is now grown on up to 3,000 ha (Agricultural statistics yearbook, 2019). Night-breaking between 10:00 p.m. and 2:00 a.m. using 23W compact fluorescent lamps is commonly used to produce off-season fruit in Taiwan (Chiu et al., 2015; Zee et al., 2004). However, climate variations, particularly in low temperature, result in unstable flowering rates and times, leading to an irregular harvest period and limited yield (Jiang et al., 2012, 2016).
In pitaya, the dormant bud under the areole may emerge as a reproductive bud (RB) or a new shoot. Before bud emergence, bud development can be classified into four stages (0–3) according to bud size, with stage 3 buds with more bracteoles indicating the formation of RBs (Jiang et al., 2016). Because the peak production season for pitaya is summer in most regions, they are considered as a long-day plants. However, photoperiod does not affect bud development in pitaya (Jiang et al., 2016) but rather regulates the type of bud that emerges. During the spring, four types of buds emerge sequentially with the gradual increase in day length: normal shoot (S), partial evocation shoot, partial evocation flower, and normal flower (F) buds (Jiang and Yang, 2015b). These buds are categorized by their phenotype and the arrangement of the areole and bracts (Jiang and Yang, 2015b), and observation of their emergence times has indicated that a long-day inductive photoperiod induces flower bud emergence, with a critical photoperiod of 12 h for red-fleshed pitaya (Jiang et al., 2012; Jiang and Yang, 2015c). Consequently, pitaya grown in countries where there is a 12 h photoperiod year-round, such as Malaysia, produce fruit throughout the year (Muas and Jumjunidang, 2015; Zainudin and Ahmad Hafiz, 2015).
In tropical regions, such as southern Taiwan and Vietnam, pitaya blooms between late spring and early autumn, so night-breaking is generally used for off-season production to extend the harvest season (Hoa et al., 2015; Hung and Huong, 2015; Jiang et al., 2012; Zee et al., 2004). However, lower temperatures reduce the success of off-season flowering, with longer night-breaking periods being needed to force flowering during the colder seasons in tropical regions (Jiang et al., 2012, 2016) and no flower bud formation occurring in spring in higher latitude subtropical regions of Israel even with extension of the day length (Khaimov and Mizrahi, 2006), indicating that an interaction between photoperiod and temperature may influence flowering during the non-inductive period.
Khaimov et al. (2012) reported that a long-day photoperiod and moderate temperature conditions have positive effects on flowering. However, the effects of ambient temperature on vegetative bud (VB) and RB development and emergence remain unclear. Therefore, the aim of this study was to clarify the effects of ambient temperature on the dormant bud stage of the areole as well as RB development and emergence under an inductive photoperiod in white-fleshed pitaya to inform off-season agricultural production processes.
Section snippets
Plant materials
This study was performed in the Kaohsiung District Agricultural Research and Extension Station, Pingtung, southern Taiwan (22°41′N, 120°31′E), from March to July 2016 and March to June 2017. The commercial white-fleshed pitaya variety “VN White” was used as the plant material, which has been widely cultivated in China, Taiwan, Vietnam, and other Southeast Asian countries since the end of the last century owing to its complete self-compatibility, high yield, and absence of plant variety rights (
Experiment I – Effects of ambient temperature on bud development and emergence
All emerging pitaya buds could be classified as VB, RB, B, or BD (Fig. 2), with no partial evocation of buds being observed. However, a few buds were aborted several days after they reached stage 3. At the start of the experiment, most buds were at stage 0, 1, or 2, with only 2.3% and 1.1% of buds in the CK and LT groups, respectively, being at stage 3 (Fig. 3). Significantly more buds developed to stage 3 in the third week after treatment in the CK group than in the LT group (Fig. 3).
Discussion
The effects of temperature on RB development have been reported in many species, such as lychee (Litchi chinensis), strawberry (Fragaria × ananassa), chrysanthemum (Chrysanthemum spp.), and prickly pear (Opuntia ficus-indica) (Gutterman, 1995; Ledesma et al., 2008; Menzel and Simpson, 1995; Nozaki and Fukai, 2008), and have been shown to vary among species. A LT is required for flowering in lychee, so too high a temperature (>20/15 °C) may lead to vegetative shoot or leafy panicle formation (
Conclusions
Here, we demonstrated that RB formation in white-fleshed pitaya under an inductive photoperiod can be separated into bud development and bud emergence, both of which are accelerated by a warm ambient temperature. Under a long-day (14 h) photoperiod, a low temperature (<27/17 °C) repressed bud development, inhibited RB emergence, and increased the time required for RB induction. However, RB emergence occurred when a temperature of approximately 29/19 °C was reached. Furthermore, a higher
CRediT authorship contribution statement
Yu-Chun Chu: Resources, Methodology, Investigation, Software, Formal analysis, Data curation, Writing - original draft. Jer-Chia Chang: Conceptualization, Supervision, Validation, Project administration, Funding acquisition, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study is granted by the Ministry of Science and Technology, Taiwan, Republic of China. Grant code. MOST-106-2313-B-005-034-MY3 (to J. C. Chang). We appreciate Miss Yi-Hsuan Hsu for her technical assistant in this experiment.
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