PRELIMINARY GENETIC CHARACTERIZATION OF SELECTED MANGROVE SPECIES IN SRI LANKA

Abstract

Mangroves are woody plants that thrive at the interface of land and sea, inhabiting harsh environmental conditions such as high temperature, strong wind, high salinity, extreme tide, and anaerobic muddy conditions. They show specialized adaptations, morphologically as well as physiologically for survival in this environment. Mangroves do not form a single phylogenetic group; instead, they have evolved independently and exhibit convergent evolution rather than shared descent. Currently, there are 21 species of mangroves remaining genetically unclassified. Therefore, this study attempted to classify selected Sri Lankan mangrove species using rbcL and matK gene markers. Specimens from six species (Rhizophora mucronata, Lumnitzera racemosa, Rhizophora apiculata, Avicennia officinalis, Lumnitzera littorea and Avicennia marina) were collected from the West Coast of the country covering wet, dry, and intermediate climatic zones. Dried specimens were submitted to the National Herbarium for further morphological identification while DNA was extracted from each leaf sample using modified CTAB method and Biospin genomic extraction kit. Although over 15 extractions were performed, most yielded low DNA concentrations and poor purity. However, Biospin kit extraction produced significantly better results with clear three genomic bands visualized of each six species through the Biospin method. PCR amplification using rbcL and matK primers confirmed higher efficiency with DNA extracted using the Biospin method. In this study, one species, Avicennia officinalis produced clear genomic bands with both extraction methods and both rbcL and matK amplification. However, other five species did not yield reliable bands with both methods. The secondary metabolites and high salt concentration of these species would have affected efficient DNA extraction. Sodium ions may bind to DNA complicating DNA extraction from mangrove plants. Interestingly, Avicennia officinalis which grows only in low-salinity environments showed better DNA yield, possibly due to reduced salt interference. This study pioneered research of its kind on mangroves in Sri Lanka and will be baseline research for optimizing DNA extraction protocols for mangroves and explore a variety of primers in future studies on genetic diversity of mangroves in Sri Lanka.