Genetic diversity and population structure in natural populations of Toona ciliata in the Uttarakhand state of Himalaya

Indian Mahogany (Toona ciliata, Family: Meliaceae) is a fast-growing and multi-purpose timber species. The species is well adapted to sub-tropical climates and generally grows in moisture-prone areas. It is frequently naturalized throughout the western sub-Himalayan tract, valleys of the outer Himalayas, and Eastern and Western Ghats and also cultivated on a fairly large scale in the plains of India, but no information about SSR-based genetic diversity and population structuring of T. ciliata in the Indian context has been available till now. Notably, population genetic analysis of T. ciliata is important for its long-term conservation, management, and genetic improvement programs. Thus, the present study was conducted to characterize natural populations of T. ciliata using simple sequence repeat (SSR) markers. In total, 444 individuals collected from 15 distant geographical locations in the western Himalayas were analyzed with 10 SSR loci. A total of 71 alleles were generated, with a mean of seven alleles, which ranged from 4 to 12 alleles for individual marker loci. Overall, a low level of genetic diversity (mean He = 0.315, range = 0.251–0.366) and high genetic differentiation (F_ST = 0.338) were recorded for the analyzed populations. Genetic clustering and STRUCTURE analysis revealed a strong genetic structure where most analyzed populations were grouped into two major clusters, indicating the existence of two gene pools. Further, the partitioning of genetic variance was significant (p ≤ 0.001) which revealed 34% of genetic variance among the populations. The Mantel test was used to estimate the genetic distance in relation to horizontal and altitudinal geographical distance, but a non-significant correlation was obtained. The results indicated that genetic distance between populations is not influenced by horizontal and altitudinal geographical distance. Overall, the study on population genetic analysis of T. ciliata will be of paramount importance to the researchers, foresters, and policymakers for guiding future conservation decisions.