Yellow pitaya [Selenicereus megalanthus (Schum. ex. Vaupel) Moran], a climbing cactus, is native to Central South America and distributed throughout Colombia, Ecuador, Peru, and Bolivia (Anderson, 2001; Mizrahi et al., 1997; Weiss et al., 1995). It is commercially produced in Colombia and Israel for local as well as European and Japanese markets (Mizrahi and Nerd, 1996, 1999; Mizrahi et al., 1997, 2002; Nerd et al., 2002b; Raveh et al., 1993; Weiss et al., 1995). In Israel, yellow pitaya flowers from October to December, and its fruits are harvested from January to mid-May (Nerd and Mizrahi, 1997; Weiss et al., 1994). Fruit development takes 13–14 weeks in fall and 22–23 weeks in winter (Nerd and Mizrahi, 1998; Tel-Zur et al., 2004).
Pitaya is becoming a popular fruit in Taiwan. Most commonly grown varieties belong to either Hylocereus undatus (Haworth) Britt. & Rose or H. polyrhizus (Weber) Britt. & Rose; both produce fruits in summer and fall (Hsu, 2004). Strategies such as breeding for winter cultivars and developing methods to regulate flowering seasons are being implemented to produce winter crops. Theoretically, night breaking by using supplemental light might lead to winter fruit production (Yen and Chang, 1997), but commercial application of such method is not yet practical. Thus, growing yellow pitaya as a new variety for winter fruit production is of interest. Geographically, Taiwan is located between 22°N and 25°N, ≈10° further south than Israel; thus, the phenology of yellow pitaya is expected to be different from that in Israel.
The effect of shoot age on floral bud formation and on fruit position is an important concern in orchard management. In cactus pears [Opuntia ficus-indica (L.) Miller], 90% of the floral buds are produced on the center and distal margins of the cladodes (Nieddu and Spano, 1992); and 1-year-old cladodes showed higher fertility than 2 year olds. Removal of spring-flushed cladodes and flowers in May to June can induce secondary flush and delay flowering for 1–2 months (Barbera et al., 1991a, 1991b; Inglese et al., 1994). In H. undatus, floral buds mainly emerge at the distal end of the shoot (Hsu, 2004) and current shoots flower either in the early part (May) or in the late part (September) of the flowering season (Jiang, 2005). Knowing the effect of canopy composition, including the age and the areole number of the shoots, on flowering period is important for productive canopy management.
Yellow pitaya is a tetraploid (2n = 44) in which meiosis occurs irregularly at anaphase I and therefore often results in reduced pollen viability. Low pollen viability causes low seed numbers per fruit even when fruit set is not a problem in self-pollinated flowers (Lichtenzveig et al., 2000). Because the fruit weight and seed number are positively correlated (Dag and Mizrahi, 2005; Weiss et al., 1994), lower seed numbers often means smaller fruits.
The objectives of the study include investigating the flowering phenology and canopy composition of yellow pitaya in subtropical Taiwan. We detailed the relative position where the floral buds emerged on shoots at different ages within the canopy. The fruit size and quality of different seasons were also compared.
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