Deciphering the genetic diversity of Avicennia officinalis L. across the salinity gradient in the Sundarbans mangrove forest of Bangladesh

Mangroves adaptive plasticity in the changing environmental conditions is of vital importance for conservation management. Genetic diversity of mangrove brings about adaptive plasticity, enabling a species to cope with different habitat conditions. The Sundarbans of Bangladesh is the largest coastal wetland and mangrove forest with diversified habitat conditions that support a wide diversity of flora and fauna. Avicennia officinalis L. is the pioneer species in mangrove succession in the low-salinity, medium-salinity and high-salinity zones of the Sundarbans. Adopting RAPD-PCR analysis, the genetic diversity of A. officinalis was studied to explore the ecotypes of this species in the Sundarbans. The genetic distances of A. officinalis between the low-salinity and medium-salinity zones (0.50) and between the low-salinity and high-salinity zones (0.52) are significantly (p < 0.05) higher than that between the medium-salinity and high-salinity zones (0.09). The expected heterozygosity of A. officinalis of medium-salinity (0.54 ± 0.14) and high-salinity zones (0.55 ± 0.10) are higher than that of low-salinity zone (0.37 ± 0.12). The genetic diversity of A. officinalis of medium-salinity (0.5417 ± 0.3167) and high-salinity (0.5458 ± 0.3189) zones is significantly (p < 0.05) higher than that of low-salinity zone (0.3750 ± 0.2313). This genetic diversity of A. officinalis bears significant ecological consequences. A. officinalis growing in the low-salinity zone is the low salt-adapted ecotype while that growing in the medium-salinity and high-salinity zones is the high salt-adapted ecotype in the Sundarbans. These two ecotypes of A. officinalis are of both in-situ and ex-situ conservation importance for the Sundarbans and coastal plantations of Bangladesh to face the climate change induced salinity regime changes in the future.