Abstract
In Thailand, Dendrobium is the most popular crop grown for cut flowers and as a pot plant for local use andexport. Some native species are used for hybrid production while some are specific to particular parts of thecountry and need to be conserved. The sequences of rDNA ITS (ITS1-5.8S-ITS2) and the matK gene were usedto reconstruct the phylogenetic relationships of 27 native Dendrobium spp. in Thailand, which are composedof 9 sections: Breviflores, Callista, Dendrobium , Distichophyllum, Formosae, Pedilonum , Rhopalanthe,Stachyobium, and Strongyle. The average levels of nucleotide divergence (p-distances) of matK and rDNA ITSsequences were 1.3% and 11.2%, respectively. The topologies of the phylogenetic trees reconstructed based onmatK and rDNA ITS sequences were slightly different. Use of the rDNA ITS sequence was shown to be a moreauthoritative systematic approach than use of the matK gene sequence in the genus Dendrobium. The result ofthe combined data (matK-rDNA ITS) was highly similar to the result from rDNA ITS. From rDNA ITS andcombined data, the twenty-seven Dendrobium spp. were clearly grouped into two clades with some differencesfrom the morphological classification. The present study provides the first molecular phylogeny of 27 nativeDendrobium species in Thailand.Key Words: molecular phylogeny, orchid, sequence divergence.IntroductionWith over 1000 species, Dendrobium is the secondlargest genus in Orchidaceae, inhabiting various geo-graphical areas in tropical and subtropical Asia and thenorth of Australia (Leitch et al., 2009). It is also one ofthe most popular orchids for commercial production ofcut flowers and pot plants, the demand for both pur-poses has drastically increased over the years. Work onDendrobium has mainly involved hybrid productionand varietal improvement for greater economic value.Approximately 8000 novel Dendrobium hybrids havebeen bred through interspecific hybridization to developnovel flower traits (Lavarack et al., 2000). In Thailand,Dendrobium is the largest orchid genus with more than
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