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.
