Variable genotypes at the cpDNA marker locus trnDT in spontaneous rejuvenation of the species complex around the European black poplar (Populus nigra L.) and its relatives collected in Germany

Abstract

Young poplars of the Aigeiros-Tacamahca-complex in spontaneous rejuvenation in Germany that grew along shores, mainly in gravel mines, were sampled and cultivated ex situ. The leaf phenotype was assessed. The cpDNA marker locus trnDT was investigated which is suitable for the genetic assignment of the chloroplast DNA to a poplar species. The results of Heinze (1998), who investigated the locus trnDT in poplars, were chosen as a reference to account for potential methodological differences between the present fragment length analysis results and that obtained with classic gel electrophoresis. The assignment of each individual to a leaf phenotype category allowed a basic differentiation of P.-nigra– or P.-deltoides- like and other leaf shapes. At the cpDNA marker locus trnDT, fragment lengths referring to the two variants described by Heinze (1998) or referring to at least one more variant were found. The third genotype is of intermediate length between the two that were described by Heinze (1998) and, very likely, the related fragments (approx. 1,065 base pairs = bp long) are specific for balsam poplar species. Quantitatively, the P.-nigra-related genotype was the most important in the present collection. It is shown that phenotypically Aigeiros-like rejuvenation does predominantly, but not in all individuals, carried the related trnDT marker fragments specific for P. nigra. The seed cloud of theAigeiros-Tacamahaca-complex resulting in the present rejuvenation sample trees was predominantly based on diaspores of P. nigra or of intra-specifi Aigeiros-hybrids. However, the section Tacamahaca has contributed to the seed cloud. The results suggest that there must be significant gene flow from alien or hybrid poplars in Germany. Further genetic investigations with microsatellite markers are carried out in the present poplar collective for more detailed quantification of the taxonomic composition.