Phalaenopsis and Doritaenopsis, hybrids between Phalaenopsis and Doritis, are collectively referred to as Phalaenopsis, the major floral crop in Taiwan for exporting. Asymbiotic culture on an agar-solidified medium is the main method for mass production. However, the high price of agar and the amount of time needed for preparing the medium result in increasing costs. Moreover, plantlets do not grow uniformly on solid medium and require added labor for grouping before subculture.
Seeds of epiphytic orchids, including Phalaenopsis, can germinate on a specific host tree in nature. However, the bark surface of the host tree plays an important role in determining whether seeds can germinate on it. Soft, spongy, water-filled bark with an uneven surface is more suitable than a smooth surface (Arditti, 1992). In addition, epiphytic orchids may also rely on mycorrhizal fungi (mycotrophy) as an additional surface of water (Yoder et al., 2000). In our laboratory, Doritaenopsis seeds germinated on the walls of the vessel where nutrient liquid remained and seeds germinated faster than those on a solid medium.
Given that in vitro liquid culture has been used successfully to cultivate a number of important nonorchids such as rhododendron (Douglas, 1984), conifers (Pâques et al., 1992), roses (Wong and Chu, 1995), and garlic (Kim et al., 2003), we explored the possibility that orchids, namely Doritaenopsis, could be cultured in this manner with optimal results. However, hyperhydricity (or vitrification) was a serious problem in long-term liquid culture (Etienne and Berthouly, 2002; Ziv, 1994). The hyperhydric materials were unable to grow into normal plants, and it was hard to recover to a normal state (Zhou, 1995). In this study, we investigated raising normal Doritaenopsis seedlings from seeds in a static liquid medium.
Daguin, F. & Letouzé, R. 1987 Vitreous plants in vitro: Relationship with ammonium content of the nutrient medium Acta Hort. 212 259 261
Dasgupta, J. & Bewley, J.D. 1982 Desiccation of axes of Phaseolus vulgaris during development causes a switch from a developmental pattern of protein synthesis to a germination pattern Plant Physiol. 70 1224 1227
Douglas, G.C. 1984 Propagation of eight cultivars of Rhododendron in vitro using agar-solidified and liquid media and direct rooting of shoots in vivo Sci. Hort. 24 337 347
Kadota, M. , Imizu, K. & Hirano, T. 2001 Double-phase in vitro culture using sorbitol increases shoot proliferation and reduces hyperhydricity in Japanese pear Sci. Hort. 89 207 215
Kataeva, N.V. , Alexandrova, I.G. , Butenko, R.G. & Dragavtceva, E.V. 1991 Effect of applied and internal hormones on vitrification and apical necrosis of different plants cultured in vitro Plant Cell Tissue Organ Cult. 27 149 154
Kermde, A.R. & Bewley, J.D. 1985 The role of maturation drying in the transition from seed development to germination. 1. Acquisition of desiccation-tolerance and germinability during development of Ricinus communis L. seeds J. Expt. Bot. 36 1906 1915
Kim, E.K. , Hahn, E.J. , Murthy, H.N. & Paek, K.Y. 2003 High frequency of shoot multiplication and blublet formation of garlic in liquid cultures Plant Cell Tissue Organ Cult. 73 231 236
Kishi, F. & Kakagi, K. 1997 Efficient method for the preservation and regeneration of orchid protocorm-like bodies Sci. Hort. 68 149 156
Marga, F. , Vebret, L. & Morvan, H. 1997 Agar fractions could protect apple shoots cultured in liquid media against hyperhydricity Plant Cell Tissue Organ Cult. 49 1 5
Murashige, T. & Skoog, F. 1962 A revised medium for rapid growth and bioassay with tobacco tissue culture Physiol. Plant. 15 473 497
Park, S.W. , Jeon, J.H. , Kim, H.S. , Park, Y.M. , Aswath, C. & Joung, J. 2004 Effect of sealed and vented gaseous microenvironments on the hyperhydricity of potato shoots in vitro Sci. Hort. 99 199 205
Pâques, M. , Bercetche, J. & Dumas, E. 1992 Liquid media to improve and reduce the cost of in vitro conifer propagation Acta Hort. 319 95 100
Pasqualetto, P. , Zimmerman, R.H. & Frodham, I. 1986 Gelling agent and growth regulator effects on vitrificaation of ‘Gala’ apple in vitro J. Amer. Soc. Hort. Sci. 111 976 980
Perry, P.L. , Ueno, K. & Shetty, K. 1999 Reversion to hyperhydration by addition of antibiotics to remove Pseudomonas in unhyperhydrated oregano tissue cultures Process Biochem. 34 717 723
Phan, C.T. & Hegedus, P. 1986 Possible metabolic basis for the developmental anomaly observed in in vitro culture, called ‘vitreous plants’ Plant Cell Tissue Organ Cult. 6 83 94
Takazawa, A. & Kozai, T. 1992 Effects of types of culture vessel with supporting materials on the growth of carnation plantlets in vitro Environ. Control Biol. 30 394 396
Tsai, W.T. & Chu, C.Y. 2004 Effect of support on the growth of Phalaenopsis seedlings in vitro Hort. Natl. Chung Hsing Univ. 29 85 97
Whitehouse, A.B. , Timothy, R.M. & Glyn, A.E. 2002 Control of hyperhydricity in Eucalytpus axillary shoot cultures grown in liquid medium Plant Cell Tissue Organ Cult. 71 245 252
Yoder, J.A. , Zettler, L.W. & Stewart, S.L. 2000 Water requirements of terrestrial and epiphytic orchid seeds and seedlings, and evidence for water uptake by means of mycotrophy Plant Sci. 156 145 150
Zhou, T.S. 1995 In vitro culture of Doritaenopsis: Comparison between formation of the hyperhydric protocorm-like-body (PLB) and the normal PLB Plant Cell Rpt. 15 181 185