Twelve nuclear microsatellite markers were used to assess the population genetic structure of the riparian pioneer tree species Populus nigra L. along the Morava River in the Czech Republic. Parentage analysis of 30 seedlings was performed to examine the extent of hybridization between P. nigra and introduced hybrid poplars and to determine the distances of pollen and seed movement. Additionally, spatial genetic structure was analysed and gene dispersal was estimated indirectly. In spite of the limited size of our studied population (65 adult trees), the apparent overall genetic diversity was high (expected heterozygosity He = 0.82) and comparable to the known diversity of P. nigra in southern Europe, where its glacial refugia were located. Introgression of Populus deltoides Bartr. ex Marsh. genes to P. nigra was confirmed, since 13% of tested seedlings descended from a Populus ×canadensis Moench female. The results of parentage analysis showed that a low percentage (20%) of offspring originated from parents located outside the study site. Dispersal distances for pollen and seeds movement ranged from 10 to 230 m and from 163 to 370 m, respectively. The study revealed significant spatial genetic structure (regression slope –0.0158), which was probably caused by limited gene flow.

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A possibility of selection of clones of the species Populus nigra L. with higher resistance to the rust Melampsora larici-populina Kleb. was tested in a set of 29 clones of P. nigra originating from individuals selected in various localities of the CR. Clones were tested in three localities for four years. Rust infection was evaluated according to a five-point scale. The two most resistant (R 1 ; R 2 ) and two most sensitive (S 1 ; S 2 ) clones were tested in laboratory conditions. The results of this test confirmed to be consistent with those obtained under field conditions. Significant differences between the progenies of resistant (R 1 × R 2 ) and sensitive (S 1 × S 2 ) parents proved the genetic control of resistance. Intermediate inheritance of resistance was found in the progenies S 1 × R 2 and R 1 × S 2 . Genetic effect of the paternal component was also expressed. A possibility of selection for resistance to M. larici-populina rust in P. nigra was proved.