Gene flow between cultivated poplars and native black poplar (Populus nigra L.): a case study along the river Meuse on the Dutch–Belgian border

For the first time and in contrast with former studies, evidence is presented for introgression of genes of Populus deltoides in the offspring of open pollinated P. nigra females. Information regarding the genetic origin of 34 seeds produced by an isolated female of P. nigra and of 29 seedlings that spontaneously colonised the banks of the river Meuse along the Dutch–Belgian border, was obtained by using a combination of informative molecular markers. Thirty-two seedlings from the open pollinated P. nigra female were identified as hybrids.