Defining Genetic Relationships of Plumeria through DNA Barcoding

The genus Plumeria L. is comprised of medicinal and horticulturally important plants, and is allegedly comprised of seven species. However, these species designations were based on research performed on herbarium material. Furthermore, invalid or unverified names are used among collectors, and unconfirmed or mislabeled specimens exist among botanical gardens. Using morphological characteristics to identify distinct species is often difficult due to variation in morphology, which can be influenced by genetic variation or the environment in which it is grown. Thus, using molecular markers to verify Plumeria species in collections will be an extremely valuable tool, but molecular markers must first be identified for Plumeria. The objective of this study is to identify DNA regions that will clearly and consistently distinguish species differences in Plumeria. A portion of the chloroplast matK gene, nuclear region (ITS 2), and intergenic spacer regions psbJ-petA and trnH-psbA were tested for their utility to distinguish Plumeria species collected from local, national, and international sources. Separate and combined molecular data sets were subjected to neighbor-joining, maximum parsimony, and maximum likelihood analyses. Analyses of individual regions indicated that intergenic spacer regions, characterized by high interspecific variation and low intraspecific variation, were better able to recover Plumeria species than matK and ITS 2. The least informative region was ITS 2. When combined with the matK region, psbJ-petA and trnH-psbA regions were able to successfully recover all Plumeria species tested. To this end, Plumeria species can be identified using these two intergenic spacer regions together. Furthermore, the combination of matK and intergenic spacer regions can now be used to infer low-level phylogenetic relationships within the genus Plumeria.