EFFECTS OF PLANT GROWTH REGULATORS ON THE VEGETATIVE GROWTH OF PITAYA CLADODES^©

Pitaya (Hylocereus undatus Britt & Rose) is a climbing cactus that is cultivated across a range of countries, including Vietnam and Nicaragua (Merten, 2003). In the Japanese archipelago, pitaya cultivation has been largely concentrated in the subtropical landscape of Okinawa Prefecture. However, many forms grown in the domestic warm region are cold tolerant and do not require greenhouse heating to prevent frost damage. Fumuro et al. (2007) and Fumuro and Sakurai (2013) reported that pitaya cultivation was possible on the Kinki University experiment farm located in Yuasa-cho, Wakayama Prefecture where daily minimum temperatures fell to about -4°C on four or five occasions during winter.
Pitaya forms flower buds on the cladodes (flattened leaf-like stems) when plants stop growing, but not during the period of elongation. Cladodes grow vigorously when young; if their growth is suppressed, flowering and yield increase incrementally. However, the cladode elongation rate declines during aging and yields are reduced in consequence.
Cultivated tree vigor is frequently controlled by application of plant growth regulators. Paclobutrazol, daminozide, and other agents are used as dwarfing agents, while gibberellin and other bioactive molecules are applied to promote growth. Little is known of the effects of these regulators on the vegetative growth of pitaya. Consequently, this study was conducted to measure the effects of growth regulators on pitaya cladode growth either through spraying plants or by application to the soil medium.