Genetic diversity and population structure of two disjunct natural populations of syzygium travancoricum gamble.

Abstract

A study was conducted to observe the reproductive biology of the critically endangered species, Syzygium travancoricum Gamble, and to compare the variation between two geographically disjunct populations of the species situated at Kalasamala and Kattilappara. A series of investigations on the phenology, floral biology, morphology, flowering, and fruit set were carried out to study the reproductive biology. The two populations were compared to assess the variation in terms of population structure, morphology, wood anatomy and seed bank. The study revealed that, flowering occurred in S. travancoricum after a dry period and the fruiting occurred just before the onset of rain. The inflorescence of the species was axillary cymose with white, calyptrate flowers. Mass flowering was observed in S. travancoricum, but, when compared to other syzygium species, number of flowers produced per tree was less. The number of flowers setting to fruits was also poor. The natural regeneration from the seeds in the site too was poor. The seeds that germinated below the trees died in the seedling stage itself. The pollen viability studies revealed that the percentage of pollen germination was poor in S. travancoricum. The analysis of the seed germination assay indicated that seed germination was also poor in the species. The germinated seeds in lab too died at the seedling stage itself. The observations related to the population comparison revealed that, there were a lot of variations between the two populations in most of the characters. The biometric characters like tree height, GBH, and crown area showed significant differences between the two populations. In the case of leaf morphological characters such as leaf length and breadth, there were significant variation between the populations. The species associated with S. travancoricum was different in Kalasamala and Kattilappara. The relative density of the species was different in the two populations. The two populations showed significant variations in the case of wood anatomical characters. The seed banks too differed significantly between the two sites. The study concluded that the constraints such as, lesser flower production, poor fruit set, lower seed germination, poor seed viability could be the main causes of the rarity of S. travancoricum. The study further showed that the two populations have considerable differences between them, either environmental or genetic.