Molecular Characterization and Phylogenetics in the Rhizophora Species Complex at Pichavaram, Tamil Nadu: A Potential Resource for Phyto-Pharmacology

Mangroves are spatially limited bioresources known for their potential pharmacological uses. The genus Rhizophora is a conspicuous one reported to have enormous biopotentials in treating inflammation, diabetes, and rheumatism. However, mangroves are recently experiencing severe threats due to the over-exploitation of valuable tannin resources, climate change, and other anthropogenic pressures. R × annamalayana, a natural hybrid in Pichavaram, is rare in its distribution and a source of bioactive compounds with anticancer properties. The pure nature of the hybrid makes it more vulnerable to extinction. Therefore, domestication, conservation, and sustainable use of valuable resources are needed on a date. Poor genetic structure in mangroves is reported to be one of the reasons for extinction. Hence, understanding the population genetic structure of the genus is of paramount importance. Therefore, the present study aimed to understand the population genetic structure of the Rhizophora species complex in Pichavaram with the following objectives, to carry out the molecular characterization of the putative hybrid and to examine the phylogenetic relationship to its parental species using microsatellite markers. The study identified that putative hybrid R. × annamalayana (mean HE = 0.592) has more significant variability than the putative parents R. apiculata (mean HE 0.611) and R. mucronata (mean HE = 0.667). The negative inbreeding coefficient value or Wright’s Index in R. × annamalayana (- 0.190) suggests ample variation among the putative hybrids. The putative hybrid is genetically more proximal to R. apiculata than R. mucronate. Phylogenetic studies indicate that ten samples out of fifteen were clustered with R. mucronata, and the rest five grouped with R. apiculata indicating the varying paternal and maternal combinations. 