Phalaenopsis orchid is one of the most valued potted ornamental plants in the world. It is usually micropropagated, produced, and sold in more than one country, thus the production of Phalaenopsis has become an international specialized industry. Plants are often transported intercontinentally in a bare-root condition due to quarantine requirements. Therefore, the transportation duration must be kept short by way of air freight. Taiwan has been certified by the U.S. Department of Agriculture since 2005 to export Phalaenopsis with potting medium to the United States under a specified process. Shipping Phalaenopsis with potting medium reduces stress during transport, thereby permitting shipment by sea freight, which much lowers costs. However, shipping plants from Taiwan to the United States by marine transport takes about 2 to 3 weeks, and the effects of long-term dark storage on Phalaenopsis physiology were not known.
Mature leaves of Phalaenopsis exhibit typical crassulacean acid metabolism (CAM) photosynthetic pathway (Endo and Ikusima, 1989; Guo and Lee, 2006; Ota et al., 1991). Some CAM plants such as Opuntia basilaris (Szarek et al., 1973) and Xerosicyos danguyi (Bastide et al., 1993; Rayder and Ting, 1983) shift their photosynthetic pattern from CAM to CAM-idling during a long period of drought. CAM-idling is defined as a damped form of CAM in which plants maintain diurnal fluctuation of organic acid by recycling respiratory CO2 without stomata opening. Under such a circumstance, the total organic acid concentration in plants gradually dropped during the drought period but rapidly recovered after rewatering (Bastide et al., 1993). The plasticity of photosynthetic status was also observed in Doritaenopsis Tinny Tender, in which net CO2 uptake rate declined with increasing period of drought and had a sudden revival after rewatering (Cui et al., 2004). However, up to the present, there has been no research related to the effects of long-term dark storage on photosynthetic status of Phalaenopsis.
Chlorophyll fluorescence is a subtle reflection of the primary processes of photosynthesis that take place in the chloroplasts (DeEll et al., 1999). Up to now, effects of dark storage (Su et al., 2001), light intensity (Lin and Hsu, 2004), growth stage (Hsu, 2007), and diurnal cycle (Pollet et al., 2009) on chlorophyll fluorescence changes in Phalaenopsis had been studied. The quantum efficiency of Phalaenopsis equestris leaf was unaffected after exposure to 25 °C with 70% or 10% relative humidity in a dark growth chamber for up to 30 d, but was reduced after exposure to 35 °C (Su et al., 2001). The study showed that Phalaenopsis is tolerant of long-term dark storage under a favorable environment, though it did not provide information on subsequent vegetative and flowering performance.
Plants, transferred from shipping container to greenhouse, often experience a sharp light intensity change. This can easily cause leaf yellowing or sunburn when higher than tolerable light intensities are provided after dark storage. As a heavily self-shading plant, lower mature leaves of Phalaenopsis are adaptive to low light, and receive less than one-sixth the light intensity of upper leaves; however, they possess the ability to reacclimate to high light (Lin and Hsu, 2004). Net photosynthetic rate of Phalaenopsis saturates at 130 to 180 μmol·m−2·s−1 photosynthetic photon flux (PPF) (Lootens and Heursel, 1998; Ota et al., 1991). Commercial growers generally provide 280 to 380 μmol·m−2·s−1 PPF to their Phalaenopsis plants (Chen and Wang, 1996). Phalaenopsis exposed immediately to the regular culturing light intensity after dark shipping may be injured.
The objectives of this study were to investigate the photosynthetic status after simulated dark shipping (SDS), to determine the effects of bare-root treatment and dark-storage duration on leaf hormonal content and post-shipping quality, and to determine the optimal light intensity for maximizing photosynthetic efficiency right after long-term dark storage of Phalaenopsis Sogo Yukidian ‘V3’.
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