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Genetic diversity and structure of Populus nigra populations in two highly fragmented river ecosystems from Turkey

European black poplar (Populus nigra L.) is an important tree species in terms of social, economic, and ecological interest in Turkey. Although large poplar plantations meet the needs of the economy, natural genetic resources of the species have been highly degraded due to anthropogenic effects such as overexploitation and habitat fragmentations. To assess genetic diversity and structure of fragmented populations, 124 naturally distributed European black poplar trees from two major rivers (Kızılırmak and Göksu) in Turkey were sampled and screened by using 20 nuclear microsatellite DNA loci. To detect the possibility of natural hybridization, 10 reference Populus deltoids L. trees were studied with six microsatellite loci. Out of 124, five trees were determined as F2 hybrids with diagnostic and informative alleles. Studied populations appear to have experienced a recent bottleneck event which is likely to cause to reduction in allelic diversity and to increase heterozygosity (mean Ho = 0.80). Four populations representing upstream, middle and downstream parts of the Kızılırmak River were found to be differentiated from Göksu river population, evidenced by genetic differentiation (FST = 0.06), geographical distances in principal coordinate analysis and clustering pattern in structure analysis. Traditional management of European black poplar coupled with bottleneck and hybridization events has played an important role in reduced genetic diversity and degradation of the genetic resources of the species in two river systems. The study has provided invaluable information to prevent further genetic degradation, to maintain existing genetic diversity of the species in its natural habitats, and to implement efficient conservation strategies and breeding programs for future generations