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Complete genome of rose myrtle, Rhodomyrtus tomentosa, and its population genetics in the Thai-Malay Peninsula

Seagrass wasting disease in the 1930s resulted in mass decline of seagrass Zostera marina in the Northern Atlantic Ocean. Labyrinthula zosterae is the potential pathogen of this disease that can lead to seagrass bed loss. This organism infects eelgrass’ leaf. Previous studies to identify the diversity of Labyrinthula spp. were based on culture method. This present study is the first study to use leaf samples for Labyrinthula molecular identification and explores diversity of the genus Labyrinthula. I investigated samples from six locations by cloning and Sanger sequencing of a 290 bp partial sequence of the 18S rDNA. Blast search against GenBank revealed that most sequences are 77-100% similar to L. zosterae, while some sequences from Wackerballig and Sandspollen were 84-94% matched Labyrinthula spp. None of that putative Labyrinthula spp. was grouped with known sequences from the database. There were seven OTUs generated. DNA extraction gave similar results for both tested extraction kits, a plant and a tissue kits. Nonetheless, the plant kit has more advantage due to its lower cost and time effort. In conclusion, this study shows undiscovered Labyrinthula spp. in the investigated eelgrass populations, second it shows that the method used in this study is suitable for further applications.

Background: The Indo-Pacific region has the largest number of seagrass species worldwide and this region is considered as the origin of the Hydrocharitaceae. Halophila ovalis and its closely-related species belonging to the Hydrocharitaceae are well-known as a complex taxonomic challenge mainly due to their high morphological plasticity. The relationship of genetic differentiation and geographic barriers of H. ovalis radiation was not much studied in this region. Are there misidentifications between H. ovalis and its closely related species? Does any taxonomic uncertainty among different populations of H. ovalis persist? Is there any genetic differentiation among populations in the Western Pacific and the Eastern Indian Ocean, which are separated by the Thai-Malay peninsula? Genetic markers can be used to characterize and identify individuals or species and will be used to answer these questions. Results: Phylogenetic analyses of the nuclear ribosomal internal transcribed spacer region based on materials collected from 17 populations in the Western Pacific and the Eastern Indian Ocean showed that some specimens identified as H. ovalis belonged to the H. major clade, also supported by morphological data. Evolutionary divergence between the two clades is between 0.033 and 0.038, much higher than the evolutionary divergence among H. ovalis populations. Eight haplotypes were found; none of the haplotypes from the Western Pacific is found in India and vice versa. Analysis of genetic diversity based on microsatellite analysis revealed that the genetic diversity in the Western Pacific is higher than in the Eastern Indian Ocean. The unrooted neighbor-joining tree among 14 populations from the Western Pacific and the Eastern Indian Ocean showed six groups. The Mantel test results revealed a significant correlation between genetic and geographic distances among populations. Results from band-based and allele frequency-based approaches from Amplified Fragment Length Polymorphism showed that all samples collected from both sides of the Thai-Malay peninsula were clustered into two clades: Gulf of Thailand and Andaman Sea. Conclusions: Our study documented the new records of H. major for Malaysia and Myanmar. The study also revealed that the Thai-Malay peninsula is a geographic barrier between H. ovalis populations in the Western Pacific and the Eastern Indian Ocean. Leibniz Universität Hannover Ministry of Education and Training, Viet Nam Prince of Songkla University Higher Education Research Promotion National Research University Project of Thailand Office of The Higher Education Commission, Universiti Putra Malaysia MOSTI/SF/1171 DFG