Evaluation of the evolutionary process within Populus caspica species from Hyrcanian forests by karyotype analysis

Caspian poplar (Populus caspica Bornm.) is distributed exclusively in the Hyrcanian forests. Hyrcanian forests are the final remnants of Tertiary temperate deciduous forests in Western Eurasia and worldwide. This species plays a significant ecological role in the protection of the natural environment in Hyrcanian forests. In this research, chromosome number and karyotype details of 11 populations of the species were investigated for the first time, using fresh root cuttings collected from mature trees in different parts of the forest, located in the northern parts of Iran. Pre-treatment, fixation, hydrolyzing, and staining were conducted by α-bromonaphthalene, carnoy’s solution, 1N HCl, and hematoxylin agent, respectively. Chromosomal data were analyzed according to a nested model based on a completely randomized design. Chromosome numbers of all of the populations were the same as 2n = 38, which mostly were medium region and sub-metacentric types. Significant differences were observed between the provinces and populations, based on chromosome length grand means, arm ratios and centromere indices. The results demonstrated that structural rearrangement has occurred within the studied populations and indicated an active evolutionary process within and between populations of the species due to natural hybridization. Also, these results showed that artificial inter-specific hybridization between the P. caspica and its relative species can be employed to broaden the ecological zone of the species.