Inhibition of Early Inflorescence Initiation in Phalaenopsis Hybrids by Photoperiod and Temperature

Abstract

Phalaenopsis hybrids are usually grown at ≥ 29°C to inhibit flower induction and maintain vegetative growth. However, this practice was consumed a large amount of energy, especially during winter season. If immature Phalaenopsis was exposed to temperature below 26°C, early flowering which has undesirable quality was occur (Lopez et al., 2007). Therefore, alternative strategies are needed to reduce energy consumption without early flowering of Phalaenopsis. This study was performed to examine the effects of 1) photoperiod and 2) minimum heating duration of 29°C on preventing inflorescence initiation in Phalaenopsis hybrids at 6-month-old or 1-year-old stages. In chapter 1, clones of 6-month-old stage Doritaenopsis Queen Beer Mantefon were grown under two controlled environment chamber maintained at 21 or 26°C. Each chamber had four growth modules providing photoperiod of 9/15 h (SD

day/night), 12/12 h (MD), 16/8 h (LD), or SD plus NI (22:00-02:00 HR) with photosynthetic photon flux densities (PPFD) 100 ± 10 and 4 ± 1 µmol•m-2•s-1 during the day and NI, respectively. In chapter 2, clones of Doritaenopsis Queen Beer Mantefon and Phalaenopsis Normans Jade Green Apple at 6-month-old or 1-year-old stages were grown in separate growth chambers with four daily durations of temperature at 29°C for 6, 12, 18, or 24 h. The photoperiod was a constant 16 h consisting of 12 h PPFD 120 ± 10 µmol•m-2•s-1 (06:00-18:00 HR) with 4 h PPFD 25 ± 10 µmol•m-2•s-1 (18:00-22:00 HR). In chapter 1, all photoperiod treatments at 26°C completely prevented inflorescence initiation, whereas 70.8, 58.3, 50.0, and 20.8% of the plants induced inflorescence when they were grown under SD, MD, NI, and LD at 21°C, respectively, after 21 weeks of treatment. The number of new leaves increased when the plants were grown at 26°C than at 21°C. However, the number of new leaves increased similar to at 26°C until 17 weeks when the plants were grown under LD at 21°C. In chapter 2, leaf span on both stages of Phalaenopsis Green Apple grown at 29°C for 12 and 18 h increased more than that of the plants grown at 29°C for 6 and 24 h. Leaf span on 6-month-old stage Doritaenopsis Mantefon increased with increasing duration of 29°C from 6 to 24 h, whereas that of 1-year-old stage plant was the longest when the plants were grown at 29°C for 18 h during 22 weeks of the treatment. Inflorescence initiation was inhibited in 6-month-old Phalaenopsis Green Apple when the plants were exposed to 29°C for 6 h or longer. 6-month-old or 1-year-old stages Doritaenopsis Mantefon and 1-year-old stage Phalaenopsis Green Apple required exposure to 29°C for 12 h or longer to inhibit inflorescence initiation. These studies indicated that LD or exposure to at least 6 to 12 h at 29 °C can prevent early flowering in immature Phalaenopsis hybrids.