Abstract

Rhododendron arboreum is an ecologically and economically important forest tree species in high altitude forests. In the Himalayan region of Northeast India, R. arboreum is extensively harvested as a source of fuelwood while selected forest stands have been set aside as protected forests by tribal groups resulting in a mosaic of harvested and protected forests. I assessed the genetic structure of R. arboreum in these forests using microsatellite markers that were originally developed for R. mettemichii . Out of eight pairs of primers evaluated, three primer pairs showed reliable amplification and polymorphism in R. arboreum . These three primer pairs or loci (RM1D1, RM2D2, and RM9D6) were used in assessing the genetic structure of R. arboreum in protected and harvested forests in the Eastern Himalayan region of Northeast India. Leaf samples collected from over 125 trees in five populations of R. arboreum representing two protected and three harvested forests, 35 different alleles were detected at three loci, with an average of 11.66 alleles per locus. There were no significant differences in number of alleles between populations. Over all populations, the mean observed and expected heterozygosity values were 0.801 and 0.804, respectively. A total of five private alleles were detected in two of the five populations (Pipraw Jang disturbed and Falokchar Mukto disturbed), suggesting private alleles are confined to harvested populations. The values of population differentiation (Fst) ranged between 0.015 and 0.057 with a corresponding gene flow (Nm) values of 15.8 and 4.1 respectively suggesting moderate levels of gene flow among populations. Population differentiation showed a significant correlation with the geographic distance. The high level of heterozygosity suggests a predominantly outcrossing mating system in R. arboreum . Although the level of population differentiation is low, the significant correlation between population differentiation (Fst) and geographic distance within a short distance of about 5 km is striking. In order to capture and maintain maximum genetic diversity, representative populations of R. arboreum distributed throughout its geographic distribution range should be conserved. These populations may serve as a seed source for regeneration of adjacent harvested forests. Further studies are needed to gain insights into the source of these private alleles as well as average distance of gene flow to determine the optimal distance for establishing protected populations of R. arboreum