The production of new and improved orchid hybrids has focused mostly on new flower colors, color patterns, and flower size and number. Over 100,000 commercial orchid hybrids have been registered worldwide to date for either the cut flower or potted plant market. The rapid expansion of the market has increased the interest of growers and customers for new and improved orchids. By 2005, the demand for orchids had placed them in second place among potted floriculture crops in the United States with wholesale revenues estimated at USD 144 million (USDA, 2006). Furthermore, commercial orchid production currently represents 8% of global floriculture trade, due to the increased demand for orchid cut flowers (Martin and Madassery, 2006).
Doritaenopsis Guillaum. & Lami is a popular hybrid between Phalaenopsis Blume and Doritis pulcherrima Lindl. and is used as a potted plant or cut flower (Tsukazaki et al., 2000). General micropropagation procedures for Doritaenopsis and Phalaenopsis have been published (Arditti and Ernst, 1993). Particularly for Doritaenopsis, in vitro propagation protocols have been developed using different explants and various concentrations of plant growth regulators. Explants used include flower stalk internodes (Lin, 1986), shoot tips of flower stalk buds (Tokuhara and Mii, 1993), dormant buds (Ernst, 1994), and root tip cultures (Park et al., 2003). Plant growth regulators used include benzyladenine (BA) (Lin, 1986), naphthalene acetic acid (NAA) combined with 6-benzylaminopurine (BAP) (Tokuhara and Mii, 1993), thidiazuron (TDZ) (Ernst, 1994), and zeatin (Park et al., 2003). Most of the studies performed to date involve the production of shoots through the formation of protocorm-like bodies (PLBs). Although PLBs can be produced from almost any part of the plant, callus formation may occur (Arditti and Ernst, 1993; Park et al., 2002), and PLBs tend to grow and develop more slowly than does direct shoot formation.
In preliminary studies we observed that various concentrations of TDZ combined with various concentrations of NAA were able to quickly induce direct shoot formation and high multiplication rates when using specific flower explants from Phalaenopsis and Doritaenopsis hybrids (W. Vendrame, unpublished data). To confirm those preliminary results, we repeated the experiment to verify the effects of four explant sources and combinations of two plant growth regulators (NAA and TDZ) at different concentrations on direct in-vitro shoot induction and multiplication in cultures of Doritaenopsis. Plant regeneration, acclimatization, survival, and establishment were also evaluated.
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