Indigenous forests of European black poplar along the Danube River: genetic structure and reliable detection of introgression

Abstract

The European black poplar (Populus nigra L.) is a tree species that once had the central role in the development of riparian ecosystems in a great part of Europe and Asia. During centuries, it is harassed by the riverside's urbanization, drainage of wetlands, and controlled river management, and compromised by intercrossing with other poplar species and cultivated hybrids. With the aim to perceive its genetic diversity and integrity along the Danube River, 12 natural P. nigra forests from corresponding protected areas were assessed using eight highly polymorphic microsatellite loci and win3 genetic marker. In the sample set, among individuals morphologically recognized as P. nigra, 2.28\% were identified as P. x euramericana hybrids and those were excluded from further analyses. High number of alleles and high heterozigosity have been observed in all populations. Only 2.95 \% of total genetic variance was recorded among populations, while the pattern of genetic differentiation corresponds to the isolation by geographic distance. It was found that one population had experienced a recent reduction in population size. We infer that genetic integrity and variation of European black poplar is not compromised within the studied areas which are, therefore, able to provide high-quality genetic material of nonhybrid P. nigra for maintaining and promoting metapopulations along the Danube River.