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Dendrobium is one of the largest genera in the Orchidaceae family. Information on the genetic diversity and relationships among species and hybrids is important for breeding purposes and species conservation. The objectives of this study were to assess genetic relatedness and to determine whether morphological, molecular, or combined analysis can discriminate among Dendrobium species, commercial hybrids, and interspecific hybrids. A total of 81 Dendrobium accessions were characterized with 12 amplified fragment length polymorphism (AFLP) primer pairs and 21 morphological characters. Mean genetic relatedness for morphological characters, AFLP analysis, and combined analysis were 0.61, 0.37, and 0.43, respectively. Dendrograms were generated using an unweighted pair group method with arithmetic averages (UPGMA); the analysis was performed on a Jaccard similarity coefficient matrix. The data from morphological characters revealed that the Jaccard similarity coefficient ranged from 0.20 to 1.0, where the tested 81 Dendrobium accessions could be grouped into four clusters. For the AFLP analysis, the number of polymorphic fragments for each primer varied from 80 to 284 with 78% average percentage of polymorphic loci and the similarity coefficient ranging from 0.125 to 1.0 with Dendrobium accessions grouped into three clusters. The similarity coefficients estimated through a combined analysis of morphological and AFLP data ranged from 0.21 to 1.0 and the Dendrobium accessions appeared clustered into two groups. The results revealed some similarities among the three data sets. The combined data set was the most useful in discriminating Dendrobium accessions based on species sections and relationship among species and their hybrids. The correlation between the AFLP data and the combined data was highly significant (r = 0.98, P > 0.001), indicating the usefulness of AFLP data for species discrimination and hybrid identity in the absence of floral morphological characters. Orchids are commercially important in Malaysia. Export value is expected to increase further because of a wider product range, longer shelf life, and ability to export flowers year-round. The orchid family is probably one of the most important plant families from a horticultural point of view. Orchidaceae is one of the largest families among angiosperms. The family includes 800 genera and 25,000 species (Stewart and Griffiths, 1995). Orchids are distributed in all regions of the world except Antarctica and are found growing in many different habitats and elevation gradients (Pridgeon, 2000). They are well known for their economic importance and widely cultivated for ornamental purposes and cosmopolitan in distribution (Bechtel et al., 1992). The genus Dendrobium is the third largest in the family Orchidaceae, comprising 1184 species worldwide (Leitch et al., 2009). Dendrobium plants are among the most prevalent orchids for commercial production of cut flowers and potted plants (Chen and Tsi, 2000) and the most popular genus in horticultural industries. The genetic diversity of the Dendrobium genus is not well known (Wang et al., 2009). Orchid classification has been poorly understood because of the lack of fossil records, the large number of species, and a historical emphasis on characters related to floral morphology. Circumscription of genera, subtribes, tribes, and subfamilies and the relationships among them were unclear because of homoplasy in morphological and anatomical features (Chase, 2006). There has been no explicit morphological cladistic analysis of Orchidaceae (Freudenstein and Rasmussen, 1999). Phylogenetic research using DNA sequences is now unraveling the complex picture at every taxonomic level. Assessment of genetic variability is important for the use of genetic resources and for determining the uniqueness of genotypes to exploit heterosis (Franco et al., 2001). Genetic diversity can be inferred from genetic similarity or distance estimates determined using phenotypic variation and/or molecular markers. Molecular markers are not subject to environmental influence, and because of that, they are considered superior to morphological markers (Máric et al., 2004). Several types of molecular markers are available and have been used in assessment of orchid genetic diversity; ribosomal DNA internal transcribed spacer (ITS) region-based analysis was used to ascertain the phylogenetic relationship among 20 Dendrobium species (Chiang et al., 2012), whereas a phylogenetic tree from ribosomal-ITS2 sequences was constructed for 18 species of the genus Dendrobium (Chaudhary et al., 2012; Wang et al., 2009) used the intersimple sequence repeat technique to evaluate genetic diversity and phylogenetic relationship among 31 Dendrobium species and Shengnan et al. (2011) determined the genetic diversity among 31 species of Dendrobium species using random amplified polymorphic DNA markers. AFLP markers are dominant markers. The AFLP technique can generate hundreds of highly replicable markers, allowing for high-resolution genotyping (Mueller and Wolfenbarger, 1999). Approximately 90% of the AFLP polymorphisms reflect point mutations and most AFLP fragments are independent loci (Buntjer et al., 2002). The loss of a restriction site removes the fragment from the profile rather than changing its size (Albertson et al., 1999), which means there is no need for prior DNA sequence information. When compared with other DNA-based markers (Vos et al., 1995), many markers can be analyzed in a short time, and only a small amount of DNA is needed. AFLP markers are highly reproducible and reliable (Bagley et al., 2001; Jones et al., 1997), high-throughput, cost-effective, and have wide genome coverage (Hansen et al., 1999; Prashanth et al., 2002). AFLP has proven to be an extremely effective tool for distinguishing closely related genotypes (Xiang et al., 2003). AFLP markers have been used in the assessment of genetic relationships in many plant species such as rice (Zhu et al., 1998), Arabidopsis thaliana (L.) (Breyne et al., 1999), bluegrass (Renganayaki et al., 2001), Carica papaya (Kim et al., 2002), Hibiscus tiliaceus (Tang et al., 2003), and potato (Esfahani et al., 2009). Received for publication 9 Sept. 2013. Accepted for publication 2 Mar. 2014. To whom reprint requests should be addressed; e-mail wicki@ukm.my. 524 HORTSCIENCE VOL. 49(5) MAY 2014 Molecular and morphological data matrices are very informative tools for the estimation of genetic distances (Vieira et al., 2007). Few orchid studies have analyzed at the same time both molecular data and morphological characters for the same set of taxa, but these have demonstrated that both types of characters are complementary and the structural characters often mark clades recovered in the combined analyses (Albert, 1994; Figueroa et al., 2008). Different studies found that the distribution of morphological character states provides additional support to the groupings recovered in molecular phylogenetic trees (Figueroa et al., 2008; Salazar, 2009; Salazar et al., 2009). The objectives of this study were to 1) determine genetic relatedness among Dendrobium accessions from different species and hybrids; and 2) determine whether morphological, molecular, or combined analysis can discriminate Dendrobium species, Dendrobium commercial hybrids, and Dendrobium interspecific hybrids. Materials and Methods Plant materials. Eighty-one Dendrobium accessions were used in this study from 13 Dendrobium species, eight commercial hybrids, and 17 interspecific hybrids. All plant materials were 2 years old. Dendrobium species were propagated by seeds or cuttings, whereas the commercial hybrids and interspecific hybrids were vegetatively propagated. Leaf samples of accessions were collected from the Malaysian Agricultural Research and Development Institute orchid greenhouse. A list of the Dendrobium accessions, their corresponding accession numbers, and classification is provided in Table 1. The geographical origin of the Dendrobium species in Malaysia is given in Nor Hazlina et al. (2013). Morphological data analysis. All plants were assessed for 21 morphological traits, all of which were referred by Sheehan and Sheehan (1994): plant height, root type, leaf type, leaf height, leaf width, pseudobulb habit, pseudobulb character, pseudobulb structure of cross-section, pseudobulb inter node, flower arrangement, flower structure, sepal structure, petal structure, flower color arrangement, hairy flowers, sepal color, sepal with more than one color, petal color, petal with more than one color, labellum color (upper side), and labellum color (inner side). All measurements were made using a digital caliper and flower color was standardized using the Royal Horticultural Society Color Chart. Average values were applied for each quantitative character. All morphological data were standardized using the Transform option in Past Version 1.92 (Hammer et al., 2001) to reduce the influence of different scales. Morphological character data were used to estimate similarity coefficients, according to Jaccard (1908) and to construct dendrograms using the UPGMA in PAST Version 1.92 software (Hammer et al., 2001). Amplified fragment length polymorphism analysis. Genomic DNA was extracted from Table 1. List of Dendrobium accessions, their corresponding accession numbers, and classification. Accessions No. Species or cultivar Section Aloi1 Dendrobium aloifolium Rchb.f. Aporum Aloi2 Dendrobium aloifolium Rchb.f. Aporum Aloi3 Dendrobium aloifolium Rchb.f. Aporum Aloi4 Dendrobium aloifolium Rchb.f. Aporum Grand1 Dendrobium grande Hook.f. Aporum Grand2 Dendrobium grande Hook.f. Aporum Grand3 Dendrobium grande Hook.f. Aporum Croc1 Dendrobium crocatum Hook.f. Pedilonum Croc2 Dendrobium crocatum Hook.f. Pedilonum Croc3 Dendrobium crocatum Hook.f. Pedilonum Croc4 Dendrobium crocatum Hook.f. Pedilonum Lamel1 Dendrobium lamellatum Lindl Pedilonum Lamel2 Dendrobiu

Genetic Relatedness among Dendrobium (Orchidaceae) Species and Hybrids Using Morphological and AFLP Markers