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

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.